Category: Class 9

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 25 Computer – An Introduction Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 25 Computer – An Introduction

9th Science Guide Computer – An Introduction Text Book Back Questions and Answers

I. Choose the correct answer.

Question 1.
………………. is an electronic device which stores data and information.
(a) Telescope
(b) Television
(c) Computer
(d) Radio
Answer:
(c) Computer

Question 2.
………………. belongs to the generation IV of the computer
(a) Microprocessor
(b) Artificial Intelligence
(c) Transistor
(d) Vaccum Tubes
Answer:
(a) Microprocessor

Question 3.
Data processing involves……………….steps.
(a) seven
(b) four
(c) six
(d) eight
Answer:
(c) six

II. Match the following:

Answer:

III. Answer briefly :

Question 1.
Define computer.
Answer:
A computer is an electronic device, which manipulates and stores data and information through commands or program codes.

Question 2.
Differentiate data and information.
Answer:
Data
Data is the set of values of qualitative and quantitative variables. The data that is fed to the computer can be text, numbers, or statistics. These data stored in computer memory cannot be used directly. It has to be processed.

Information
The information we get or obtain or receive using the data from the computer can be used directly.

Question 3.
What is data processing?
Answer:
The data processing in a computer is collecting data and converting it into information according to our needs and requirements.

IV. Answer in detail :

Question 1.
What are the different steps involved in data processing?
Answer:
Data processing has six steps. They are,

• Data collection
• Data storage
• Data sorting
• The data processing
• Data analysis
• Data presentation and conclusions

Question 2.
List out the generations of computers.
Answer:
The history of computers has been classified into many stages. The main difference between the generations is the speed and efficiency of the computer. On the basis of performance and speed, the generations of the computer was categorised as follows.

Generations of Computer:

9th Science Guide Computer – An Introduction Additional Important Questions and Answers

I. Choose the correct answers :

Question 1.
The people of China used ……………….
(a) abacus
(b) transistor
(c) vacuum tubes
(d) microprocessors
Answer:
(a) abacus

Question 2.
ENIAC computer had approximately ………………. vacuum tubes.
(a) 16,000
(b) 14,000
(c) 18, 000
(d) 12,000
Answer:
(c) 18,000

Question 3.
ATM machine works with the help of …………… only.
(a) calculator
(b) mobile
(c) transistor
(d) computer
Answer:
(d) computer

Question 4.
How many generations of computers are there?
(a) 2
(b) 5
(c) 3
(d) 6
Answer:
(b) 5

Question 5.
………………. was used by the American Military.
(a) ENIAC
(b) Computer
(c) Transistor
(d) Calculator
Answer:
(a) ENIAC

Question 6.
The main difference between the generations is the ………… and …………….. of the computer.
(a) size, shape
(b) hardware, software
(c) speed, efficiency
(d) shape, performance
Answer:
(c) speed, efficiency

Question 7.
………….. is one of the steps in the data processing.
(a) Data management
(b) Data storage
(c) Data calculation
(d) Data transformation
Answer:
(b) Data storage

Question 8.
………………….. stored in computer memory cannot be used directly.
Information
a) Information
(b) Words
(c) Data
(d) Numbers
Answer:
(c) Data

Question 9.
Which of the following is the period of the first generation of computers?
(a) 1956- 1963
(b) 1964- 1971
(c) 1940- 1956
(d) 1972-2010
Answer:
(c) 1940 – 1956

Question 10.
(i) The computer operates by the exchange of commands between hardware and
software.
(ii) Lady Augusta Ada Lovelace gave the first programming to do arithmetic operations.
(a) Both the statements are Wrong
(b) Statement (i) is correct but’ statement (ii) is wrong
(c) Statement (i) is wrong but statement (ii) is correct
(d) Both the statements are correct
Answer:
(d) Both the statements are correct

II. Match the following :

Answer:

III. Answer briefly:

Question 1.
Define ENIAC.
Answer:

• ENIAC (Electronic Numerical Integrator And Computer) was designed in the year 1946 was equivalent to the size of a huge classroom.
• ENIAC had approximately 18,000 vacuum tubes.
• ENIAC, which was used by the American Military in 1946 to predict the trajectory of artillery shells, recognized as the world’s first general-purpose computer.

Question 2.
What is meant by hardware and software?
Answer:

• The computer operates by the exchange of commands between the hardware and software.
• Hardware can be touched and felt.
• The software cannot be touched and felt.

Question 3.
Name the fields where computers are used.
Answer:
The fields where computers are used are:

• Banks
• Hospitals
• Post offices
• Transport
• Market
• Media
• Defense sector
• Education and space research

IV. Answer in detail :

Question 1.
Explain the history of computers.
Answer:

• Around 2000 years ago, the people of China used Abacus.
• This was considered as the most basic model of a computer.
• Nineteenth century was considered as the birth of the computer when Charles Babbage designed the basic construction of a computer.
• ENLAC, which was used by the American Military in 1946 to predict the trajectory of artillery shells, recognized as the world’s first general-purpose computer.
• ENIAC had approximately 18,000 vacuum tubes.
• The size occupied by the ENIAC could be equivalent to a classroom.
• Lady Augusta Ada Lovelace was honored as the first programmer as she gave the first programming to do arithmetic operations.

Question 2.
Write the history of computers.
Answer:

• Around 2000 years ago, the people of China used Abacus. This was considered as the most basic model of a computer.
• Nineteenth-century was considered as the birth of the computer when Charles Babbage designed the basic construction of a computer.
• ENIAC, which was used by the American Military in 1946 to predict the trajectory of artillery shells was recognized as the world’s first general-purpose computer.
• Lady Augusta Ada Lovelace was honored as the first programmer as she gave the first programming to do arithmetic operations.

Question 3.
Explain in detail about data and data processing.
Answer:
Data:

• Data is the set of values of qualitative and quantitative variables.
• The data that is fed to the computer can be text, numbers or statistics.
• These data stored in computer memory cannot be used directly.
• It has to be processed.

Data Processing:
The data processing in a computer is collecting data and converting it into information according to our needs and requirements.

Steps in data processing:
Data processing has six steps. They are:

• Data collection
• Data storage
• Data sorting
• Data processing
• Data analysis
• Data presentation and conclusions

Question 4.
What are the different generations of computers?
Answer:

• The main difference between the generations is the speed and efficiency of the computer.
• On the basis of performance and speed, the generations of the computer were categorised.

Generations of Computer:

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 26 Parts of Computer Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 26 Parts of Computer

9th Science Guide Parts of Computer Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which one of the following is an output device?
(a) Mouse
(b) Keyboard
(c) Speaker
(d) Pendrive
Answer:
(c) Speaker

Question 2.
Name the cable that connects CPU to the Monitor.
(a) Ethernet
(b) VGA
(c) HDMI
(d) USB
Answer:
(b) VGA

Question 3.
Which one of the following is an input device?
(a) Speaker
(b) Mouse
(c) Monitor
(d) Printer
Answer:
(b) Mouse

Question 4.
Which one of the following is an example for wireless connections?.
(a) Wi-Fi
(b) Electric wires
(c) VGA
(d) USB
Answer:
(a) Wi-Fi

Question 5.
Pen drive is a/an ………….. device.
(a) output
(b) input
(c) storage
(d) connecting cable
Ans :
(c) storage

II. Match the following:

Question 1.

Answer:

III. Answer briefly :

Question 1.
Name the parts of a computer.
Answer:
Three parts of the computer are:

1. Input Unit
2. Central Processing Unit (CPU)
3. Output Unit.

Question 2.
Bring out any two differences between input and output devices.
Answer:
Input devices

1. The Input units help to send the data and commands for the processing.
2. Input devices only allow for the input of data to a computer.

Output devices

1. The Output units convert the command received by the computer in the form of binary signals into easily understandable characters.
2. Output devices only receive the output of data from another device.

9th Science Guide Parts of Computer Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
………………… plays an important role in a computer as an input device.
(a) Keyboard
(b) Scanner
(c) Printer
(d) Mouse
Answer:
(a) Keyboard

Question 2.
………………….. is an essential part of the computer.
(a) Keyboard
(b) CPU
(c) Mouse
(d) Wi-Fi
Answer:
(c) Mouse

Question 3.
A bit has a single binary value either ……………….. or ………………..
(a) 1,-1
(b) 0,1
(c) 1,2
(d) 2,0
Answer:
(b) 0,1

Question 4.
The personal computer comes under the ……………….. computer.
(a) mainframe
(b) mini
(c) micro
(d) super
Answer:
(c) micro

Question 5.
………………..cable transmits high quality and high bandwidth streams of audio and video.
(a) VGA
(b) USB
(c) Data
(d) HDMI
Answer:
(d) HDMI

Question 6.
………………..is used to connect the speaker to the computer.
(a) Audio jack
(b) Power card
(c) Data cable
(d) USB cable
Answer:
(a) Audio jack

Question 7.
………………..cable helps to establish internet connectivity.
(a) Power card
(b) Audio jack
(c) Ethernet
(d) USB
Answer:
(c) Ethernet

II. Answer the following :

Question 1.
What are the input devices?
Answer:
The input unit helps to send the data and commands for processing. The devices that are used to enter data are called injfut devices.

Question 2.
Write some examples of input and output devices of a computer system.
Answer:
Input devices:
Keyboard, Mouse, Scanner, Barcode reader, Microphone, Web camera, Light pen are some of the input devices.

Output devices:
Monitor, Printer, Speaker, Scanner, are some of the output devices.

Question 3.
What is Keyboard?
Answer:

• The keyboard plays an important role in a computer as an input device.
• Numbers and alphabet play a role of data in the computer.
• The keyboard helps to enter data.;
• Keyboard has two types of keys, namely number keys and alphabet keys.
• The keys with numbers are called number keys and the keys with letters are called alphabet keys.

Question 4.
Explain CPU.
Answer:
CPU (Central Processing Unit)

(i) Memory Unit
(ii) Arithmetic Logic Unit (ALU)
(iii) Control Unit

(i) Memory Unit: The memory unit in the computer saves all data and information temporarily. The data is measured in units which is called as Bit. A Bit has a single binary value either 0 or 1. We can classify memory unit into two types namely primary and secondary memory. Memory can be expanded externally with the help of Compact Disk (CD), Pendrive, etc.

(ii) Arithmetic Logic Unit : Arithmetic and Logic unit performs all arithmetic computations like addition, subtraction, multiplication and division.

(iii) Control Unit: The control unit controls the functions of all parts of the computer.

Question 5.
What is Bit?
Answer:
The memory unit in the computer saves all data and information temporarily. The data is measured in units which is called as Bit.

Question 6.
What are the types of monitors?
Answer:
There are two types of monitors namely.

1. Cathode Ray Tube monitors (CRT)
2. Thin Film Transistor Monitors (TFT)

Question 7.
What is the classification of the computer?
Answer:
The computers can be classified as follows based on their design, shape, speed, efficiency, working of the memory unit, and their applications.

• Mainframe Computer
• Mini Computer
• Micro or personal compute
• Supercomputer

Question 8.
Explain the types of cables.
Answer:
Video Graphics Array (VGA), High Definition Multimedia Interface (HDMI), Universal Serial Bus (USB), Data cable, Power Cord, Mic cable, Ethernet cable.

• VGA Cable: It is used to connect the computer monitor with the CPU.
• USB cable /cord: Devices like Printer, Pendrive, Scanner, Mouse, Keyboard, web camera, and Mobile phone devices are connected with the computer using a USB cord or cable.
• HDMI Cable: HDMI cable transmits high quality and high bandwidth streams of audio and video. It connects the monitor, projector with the computer.
• Data Cable: Data cable transmits data and it is used to connect a tablet, mobile phone to the CPU for data transfer.
• Audio jack: The audio jack is used to connect the speaker to the computer.
• Power cord: Power cord temporarily connects an appliance to the main electricity supply.
• Mic cable: To connect the Mic (Microphone) to the CPU, Mic wire/cord is used.

Question 9.
Explain wireless connections.
Answer:
Bluetooth, Wi-Fi is used to connect to the internet without using any connecting cables/devices.

• Bluetooth: Mouse, Keyboard can be connected to the computer using Bluetooth. Using Bluetooth the data can be shared with nearby devices.
• Wi-Fi: Net connectivity can be obtained using Wi-Fi without any connecting cables. Any data from anywhere can be shared using Wi-Fi.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 27 Hardware and Software Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 27 Hardware and Software

9th Science Guide Hardware and Software Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Find out the part which is not found in CPU?
(a) Mother Board
(b) SMPS
(c) RAM
(d) Mouse
Answer:
(d) Mouse

Question 2.
Which of the following is correct?
(a) Free and Open source
(b) Free and Traditional software
(c) Passive and Open source
(d) Passive and Traditional source
Answer:
(a) Free and Open source

Question 3.
LINUX is a
(a) Paid Software
(b) Licensed Software
(c) Free and Proprietary software
(d) Free and Open source software
Answer:
(d) Free and Open source software

Question 4.
Find out the Paid and Proprietary software from the given list
(a) Windows
(b) MAC OS
(c) Adobe photoshop
(d) All the above
Answer:
(d) All the above

Question 5.
……………… is an Operating system.
(a) Android
(b) Chrome
(c) Internet
(d) Pendrive
Answer:
(a) Android

II. Match the following :

Answer:

III. Answer in brief:

Question 1.
What are Hardware and Software?
Answer:
Hardware is the parts of a computer which we can touch and feel. Hardware includes Input and Output devices, Cabinet, Hard Disk, Mother Board, SMPS, CPU, RAM, CD Drive, and Graphics Card.

Software is programmed and coded applications to process the input information. The software processes the data by converting the input information into coding or programmed language.

Question 2.
What do you mean by Operating System? How does it work?
Answer:
Operating System (System software): Operating system is software that makes the 1 hardware devices process the data fed by the user.
Working of Operating system: It works by displaying the results on the output devices ‘ like Monitor.

Question 3.
What is Free and Open Source Software? Give any two examples.
Answer:
Free and open software is available free of cost and can be shared with many end-users. Free software is editable and customizable by the user and this leads to the update or development of new software. Examples of Free and Open source software are LINUX, Open office, Geogebra, etc.

9th Science Guide Hardware and Software Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
The Software gives …………… in the monitor.
(a) input
(b) output
(c) a & b
(d) None of these
Answer:
(b) output

Question 2.
Word Processing Software is ………………
(a) Application Software
(b) System Software
(c) Hardware
(d) None of these
Answer:
(a) Application software

Question 3.
Windows is ……………..
(i) Application Software
(ii) Operating System
(iii) Free and Open-source Software
(iv) Paid and Proprietary Software
(a) i and ii
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer:
(d) (ii) and (iv)

Question 4.
Which one of the following is an Application Software?
(a) Mac
(b) Chrome
(c) Windows
(d) Android
Answer:
(b) Chrome

II. Fill in the blanks :

1. Graphic Card is a …………….
Answer:
Hardware

2. The Software processes the data by converting the input information into coding (or) programming ……………..
Answer:
Language

3. Free software is…………….. and …………….. by the user.
Answer:
editable, customizable

4. The application programmes can be installed in the …………….. for usage on a particular computer.
Answer:
Hard Disk

III. State whether true or false. If false, correct the statement:

1. The functions of Hardware and Software are separate.
Answer:
False.
Correct statement: The functions of Hardware and Software combine together.

2. We cannot see the functions of Software.
Answer:
False.
Correct statement: We can see the functions of the software in the form of output.

3. Application Software completes more than one work of the end-user.
Answer:
True.

4. The end users can legally use the pirated version of the paid and proprietary software.
Answer:
False.
Correct statement: The end users are legally prohibited to use the pirated versions of the paid and proprietary software.

IV. Assertion and Reason type questions : 

Mark the correct choice as :
(a) If both assertion and reason are hue and Reason is the correct explanation of Assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.

Question 1.
Assertion (A) : The functions of hardware and software combine together to make the computer functional.
Reason (R) : A computer is a device comprising both hardware and software.
Answer:
(a) Both assertion and reason are true and Reason is the correct explanation of Assertion

Question 2.
Assertion (A) : The free and open-source software cannot be updated (or) developed to new software.
Reason (R) : Free software is editable and customizable by the user.
Answer:
(d) Assertion is false but the reason is true
Assertion (A) : The free and open-source can be updated (or) developed to new software.

V. Answer very briefly :

Question 1.
How are parts of a computer compared to humans?
Answer:
A computer is like a human body, where the human body is the hardware and the soul is the Software.

Question 2.
What are the two forms of the operating system and application software?
Answer:
The Operating system and application software are available in two forms.
They are:

• Free and Open-source.
• Paid and Proprietary Software.

Question 3.
WhatisOSI?
Answer:
The Open Source Initiative (OSI), is an organization dedicated to promoting Open Source Software.

VI. Answer in detail :

Question 1.
What is Application software? How is it utilised?
Answer:
Application software is a program (or) a group of programs designed for the benefit of the end-user to work on a computer.

UTILISATION:

• The application programs can be installed on the hard disk for usage on a particular computer.
• This type of application program completes one or more than one works of the end-user.
  The following are examples of the application program:
  (e.g) Drawing tools, Editing software, Word Processing Software, Video player, Audio player, etc.

Question 2.
Write the conditions in the use of Paid and Proprietary Software.
Answer:
Conditions of Paid and Proprietary Software :

• The software needs a license to use it.
• We have to pay to use the software permanently (or) temporarily.
• The end-user is legally prohibited to steal the software program.
• The end-user is also prohibited to use the pirated versions of the software.
  (e.g.) Windows, Microsoft Office, Adobe Photoshop.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 14 Acids, Bases and Salts Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

9th Science Guide Acids, Bases and Salts Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Zn + 2HCl → ZnCl₂ + ….↑ (H₂, O₂, CO₂)
Answer:
H₂

Question 2.
Apple contains malic acid. Orange contains …………………(citric acid, ascorbic acid).
Answer:
ascorbic acid

Question 3.
Acids in plants and animals are organic acids. Whereas Acids in rocks and minerals are …………………. (Inorganic acids, Weak acids).
Answer:
Inorganic acids

Question 4.
Acids turn blue litmus paper to …………….. (green, red, orange).
Answer:
Red

Question 5.
Since metal carbonate and metal bicarbonate are basic, they react with acids to give salt and water with the liberation of ……………….. (NO₂, SO₂, CO₂).
Answer:
CO₂

Question 6.
The hydrated salt of copper sulphate has …………….colour (red, white, blue).
Answer:
Blue

II. Answer in briefly :

Question 1.
Classify the various types of Acids based on their sources.
Answer:
The acids are classified based on their sources and organic and inorganic acids.
Organic acids – acids present in plants and animals.
Inorganic acids – acids prepared from rocks and minerals.

Question 2.
Write any four uses of acids.
Answer:

• Sulphuric acid is called King of Chemicals because it is used in the preparation of many other compounds. It is used in car batteries also.
• Hydrochloric acid is used as a cleansing agent in toilets.
• Citric acid is used in the preparation of effervescent salts and as a food preservative.
• Nitric acid is used in the manufacture of fertilizers, dyes, paints and drugs.
• Oxalic acid is used to clean iron and manganese deposits from quartz crystals. It is also used as bleach for wood and removing black stains.
• Carbonic acid is used in aerated drinks.
• Tartaric acid is a constituent of baking powder.

Question 3.
Give the significance of p^H of .soil in agriculture.
Answer:
In agriculture, the p^H of soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.

Question 4.
What are the various uses of Aquaregia.
Answer:

• It is used chiefly to dissolve metals such as gold and platinum.
• It is used for cleaning and refining gold.

Question 5.
What are the uses of Plaster of Paris?
Answer:

• It is used for plastering bones.
• It is used for making casts for statues.

Question 6.
Two acids ‘A’ and ‘B’ are given. Acid A gives one hydrogen ion per molecule of the acid in solution. Acid B gives two hydrogen ions per molecule of the acid in solution.
(i) Find out acid A and acid B.
(ii) Which acid is called the King of Chemicals?
Answer:
(i) Acid A – HCl – Hydrochloric acid. Acid B – H₂SO₄ – Sulphuric acid.
(ii)Sulphuric acid – H₂SO₄.

Question 7.
Define aquaregia.
Answer:
It is the mixture of hydrochloric acid and nitric acid prepared optimally in a molar ratio of 3 : 1.

Question 8.
Correct the mistakes :
(a) Washing soda is used for making cakes and bread soft, spongy.
(b) Calcium sulphate hemihydrate is used in textile industry.
Answer:
(a) Baking soda (Sodium bicarbonate – NaHCO₃) is used for making cakes and bread soft spongy, (or) Washing soda is used for softening hard water.
(b) Calcium sulphate hemihydrate (CaSO₄, 1/2 H₂O)is used for plastering bones (or) Bleaching powder (Calcium oxy Chloride – CaOC₁₂) is used in textile industry.

Question 9.
What is neutralization reaction? Give an example.
Answer:
Neutralization reaction is a reaction in which an acid reacts with a base to form salt and water and H⁺ ion and OH^– ion combines to generate water. The neutralization of a strong acid and strong base has a p^Hequal 7.

III. Answer in detail :

Question 1.
Differentiate hydrate and anhydrous salts with examples.
Answer:

Question 2.
Give the tests to identify Acids and Bases.
Answer:

• Acids turn blue litmus. Red bases turn red litmus blue.
• In acid phenolphthalein is colourless. In base Phenolphthalein is pink in colour.
• In acid methyl orange is pink. In bases methyl orange is yellow

Question 3.
Write any four uses of bases.
Answer:

• Sodium hydroxide is used in the manufacture of soap.
• Calcium hydroxide is used in the whitewashing of buildings.
• Magnesium hydroxide is used as a medicine for a stomach disorder.
• Ammonium hydroxide is used to remove grease stains from cloth.

Question 4.
Write any five uses of salts.
Answer:
Common Salt (NaCl) :
It is used in our daily food and used as a preservative
Washing Soda (Sodium Carbonate – Na₂CO₃) :

• It is used in softening hard water.
• It is used in glass, soap and paper industries.

Baking Soda (Sodium bicarbonate -NaHCO₃):

• It is used in making of baking powder which is a mixture of baking soda and tartaric acid.
• It is used in soda-acid fire extinguishers.
• Baking powder is used to make cakes and bread, soft and spongy.
• It neutralizes excess acid in the stomach and provides relief.

Bleaching powder (Calcium Oxychloride – CaOCl₂):

• It is used as a disinfectant.
• It is used in textile industry for bleaching cotton and linen.

Plaster of Paris (Calcium Sulphate Hemihydrate – CaSO₄ .1/2 H₂O):

• It is used for plastering bones
• It is used for making casts for statues.

Question 5.
Sulphuric acid is called King of Chemicals. Why is it called so?
Answer:
Sulphuric acid is called King of Chemicals because it is used in the preparation of many other compounds

Intext Activities

ACTIVITY – 2

Take solutions of hydrochloric acid or sulphuric acid. Fix two nails on a cork and place the cork in a 100 ml beaker.
Connect the nails to the two terminals of a 6 V battery through a bulb and a switch as shown in Figure. Now pour some dilute HCl in the beaker and switch on the current. Repeat the activity with dilute sulphuric acid, glucose and alcohol solutions. What do you observe now? Does the bulb glow in all cases?

Answer:

• The bulb glows when sulphuric acid and hydrochloric acid are used.
• The bulb does not glow when the activity is done with alcohol and glucose solution.

ACTIVITY – 3

Collect the following samples from the science laboratory – Hydrochloric acid, Sulphuric acid and Nitric acid, Sodium hydroxide, Potassium hydroxide. Take 2 ml of each solution in a test tube and test with a litmus paper and indicators phenolphthalein and Methyl orange. Tabulate your observations.

Answer:

ACTIVITY-4

Answer:

ACTIVITY – 5
Boil about 100 ml of groundwater in a vessel to dryness. After all the water get evaporated observe the inner wall of the vessel. Can you observe any deposits? This is the deposit of dissolved salts present in water.
Answer:
This is the deposit of dissolved salts present in water.

9th Science Guide Acids, Bases and Salts Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Acid secreted in our stomach is ……………….
(a) hydrochloric acid
(b) sulphuric acid
(c) nitric acid
(d) carbonic acid
Answer:
(a) hydrochloric acid

Question 2.
Hydrochloric Acid reacts with metal bicarbonates to give ……………
(a) metal chloride
(b) water
(c) carbon di – oxide
(d) all the above
Answer:
(d) all the above

Question 3.
…………… & ………….. metals do not react with HCl or HNO₃.
(a) Gold & Magnesium
(b) Silver & Magnesium
(c) Gold & Silver
(d) Zinc & Silver
Answer:
(c) Gold & Silver

Question 4.
The molar ratio of hydrochloric acid and nitric acid in aquaregia is ………………..
(a) 1 : 3
(b) 6 : 3
(c) 2 : 3
(d) 3 : 1
Answer:
(d) 3 : 1

Question 5.
Bases ionise in water to form ……………………. ions.
(a) H⁺
(b) H₃O⁺
(c) OH^–
(d) O^2-
Answer:
(c) OH ^–

Question 6.
Which of the following pairs are weak base?
(a) NH₄OH & NaOH ‘
(b) Ca(OH)₂ & KOH
(c) NH₄OH & Ca(OH)₂
(d) NaOH&KOH
Answer:
(c) NH₄OH & Ca(OH)₂

Question 7.
NaOH & KOH are …………….
(a) strong bases
(b) metal Oxides
(c) weak bases
(d) diacidic bases
Answer:
(a) strong bases

Question 8.
Which of the following solution is soapy to touch?
(a) Acidic
(b) Basic
(c) Salt
(a(d) Aquaregia
Answer:
(b) Basic

Question 9.
Which of the following solutions do not conduct electricity?
(a) alcohol
(b) glucose
(c) sulphuric acid
(d) both a & b
Answer:
(d) both a & b

Question 10.
The p^H value of neutral solution is ………………
(a) = 7
(b) <7
(c) none of the above
(d) -7
Answer:
(a) = 7

Question 11.
The p^H of stomach fluid is ……………….
(a) 4
(b) 2
(c) 6
(d) 7
Answer:
(b) 2

Question 12.
A salt which is formed by complete neutralization of an acid and a base is called ………………. salt.
(a) basic
(b) acid
(c) double
(d) normal
Answer:
(d) normal

Question 13.
The number of water molecules present in one molecule of copper sulphate is
(a) 2
(b) 3
(c) 4
(d) 5
Answer:
(d) 5

Question 14.
The molecular formula of copper sulphate pentahydrate is ………………..
(a) CuSO₄. H₂O
(b) CuSO₄. 2H₂O
(c) CuSO₄. 5H₂O
(d) CuSO₄. 3H₂O
Answer:
(c) CuSO₄ . 5H₂O

Question 15.
……………is the gas produced when HCl is added with carbonate salt.
(a) H₂
(b) N₂
(C) CO₂
(d) O₂
Answer:
(c)CO₂

Question 16.
The formula of bleaching powder is ……………..
(a) CaCl₂
(b) CaOCl₂
(c) Ca(OH)₂
(d) CaO
Answer:
(b) CaOCl₂

Question 17.
The chemical name of plaster of paris is ……………………..
(a) Calcium sulphate hemihydrate
(b) Calcium sulphate monohydrate
(c) Calcium sulphate dihydrate
(d) Calcium sulphate trihydrate
Answer:
(a) Calcium sulphate hemihydrate

Question 18.
Which of the following metal does not react with sodium hydroxides?
(a) Cu
(b) Ag
(c) Cr
(d) All the above
Answer:
(d) All the above

Question 19.
Curd contains …………….acid.
(a) malic ‘
(b) formic
(c) lactic
(d) ascorbic
Answer:
(c) lactic

Question 20.
Which one of the following acids undergoes complete ionisation?.
(a) HCl
(b) CH₃COOH
(c) H₂SO₄
(d) all the above
Answer:
(a) HCl

II. Fill in the blanks :

1. Acid reacts with base to form a neutral product called ………………
Answer:
Salt

2. The taste of acid is ………………..
Answer:
Sour

3. …………….. contain one or more replaceable hydrogen atoms.
Answer:
Acids

4. ………………..acids have a relatively smaller amount of acids dissolved in a solvent.
Answer:
Dilute

5. Acids react with metallic oxides to produce ……………….
Answer:
salt and water

6. _________ acid is used in aerated drinks.
Answer:
Carbonic acid

7. Chemical formula of aquaregia is ________
Answer:
3HCl + HNO₃

8. Water soluble bases are called ________
Answer:
alkali

9. Non-metallic oxides are ___________ in nature.
Answer:
acid

10. __________ are bitter in taste.
Answer:
Bases

11. __________ alkali has a relatively high percentage of alkali in its aqueous solution.
Answer:
Concentrated

12. Acids turn blue litmus to ………….
Answer:
red

13. Phenolphthalein and methyl Orange are ………………
Answer:
indicators

14. p^H stands for …………….. in a solution.
Answer:
power of hydrogen ion concentration

15. The p^H value of acids are …………….. than 7.
Answer:
lesser

16. White enamel coating of our teeth is…………….
Answer:
Calcium phosphate

17. Salt is ………….. in nature.
Answer:
hygroscopic

18. Salt which is formed by the partial replacement of hydrogen ions of an acid by a metal is called ………………………..
Answer:
acid salt

19 Salts contaíning water of crystallisation are called …………. salts.
Answer:
hydrated

20. Salts that do not contain water of crystallisation is called …………..
Answer:
anhydrous salt

21. p^H value of human blood is ……………..(7.0, 7.4, 7.6).
Answer:
7.4

22. The nature of the toothpaste commonly used is ……………. in nature (acidic, basic, neutral)
Answer:
basic

23. You are given pure water to test the p^H value using p^H paper. It shows colour (White, black, green)
Answer:
green

III. To Match:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Question 4.

Answer:

IV. Complete the following equations.

Question 1.
HCl + H₂O → ? + ?
Answer:
HCl + H₂O → H₃O⁺ + Cl^–

Question 2.
H⁺ + H₂O → ?
Answer:
H⁺ + H₂O → H₃O⁺

Question 3.
Mg+ ? → ? + H₂
Answer:
Mg + H₂SO₄ → MgSO₄ + H₂↑

Question 4.
Na₂CO₃ + 2HCl → ? + ? + CO₂↑
Answer: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑

Question 5.
ZnO + 2HCl → ? + ?
Answer:
ZnO + 2HCl → ZnCl₂ + H₂O↑

Question 6.
Zn + ? → Na₂ZnO₂ + H₂ ↑
Answer:
Zn + 2NaOH → Na₂ZnO₂+ H₂↑

Question 7.
CaO + H₂SO₄ → ? + H₂O
Answer:
CaO + H₂SO₄ → CaSO₄ + H₂O

Question 8.
HCl + ? → NaCl + H₂O
Answer:
HCl + NaOH → NaCl + H₂O

Question 9.
Ca(OH)₂ + ? → ? + H₂O
Answer:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Question 10.

Answer:
A = NH₄Cl, B = NH₃↑
C = HCl
D = NaHSO₄,E = H₂O

V. Answer in briefly :

Question 1.
What are organic acids? Given examples.
Answer:
Acids present in plants and animals (living things) are organic acids.
Example: HCOOH, CH₃COOH

Question 2.
How are acids classified based on ionisation? Give examples.
Answer:
Acids get ionise in water (produce H⁺ ions) completely or partially. Based on the extent of ionisation, acids are classified as follows:
Strong Acids:
These are acids that ionise completely in water.
Example: HCl

Weak Acids :
These are acids that ionise partially in the water.
Example: CH₃COOH.

Question 3.
What is Aquaregia? Mention its uses.
Answer:
It is a mixture of hydrochloric acid and nitric acid prepared optimally in a molar ratio of 3:1. It is a yellow-orange fuming liquid. It is a highly corrosive liquid, able to attack gold and other resistant substances.

• Aquaregia is used tp dissolve noble metals such as gold, platinum, and palladium.
• It is used Tor cleaning and refining gold.

Question 4.
What does the acidity of base mean?
Answer:
It means the number of replaceable hydroxyl groups present in one molecule of a base.

Question 5.
What is Potash alum? Write its formula.
Answer:
Potash alum is a mixture of potassium sulphate and aluminium sulphate. KAl(SO₄)₂.12H₂O.

Question 6.
What are double salts? Give an example?
Answer:
Double salts are the salts formed by the combination of the saturated solution of two simple salts in equimolar ratio followed by crystallization. For example : Potash alum.

Question 7.
What are basic salts? Give suitable reaction for this.
Answer:
Basic salts are the product formed by the partial replacement of hydroxide ions of a diacidic or triacidic base with an acid radical.
Pb(OH)₂ + HCl → Pb(OH)Cl + H₂O

Question 8.
Why are tooth pastes basic?
Answer:
Toothpastes which are generally basic and used for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Question 9.
What is water of crystallisation?
Answer:
Many salts are found as crystals with water molecules they contain. These water molecules are known as water of crystallisation.

Question 10.
Why do blue colour copper sulphate becomes white on heating?
Answer:
On heating, blue colour copper sulphate loses its water molecules and becomes white.

Question 11.
Acidic or basic solutions are good conductors of electricity. Justify your answer.
Answer:
Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.

Question 12.
What are hygroscopic substances?
Answer:
Substance which absorbs water from the surroundings are called hygroscopic substances.

Question 13.
Define indicator. Give examples
Answer:
Chemical substances used to find out whether the given solution is acid or base are called indicators. Eg: Phenolphthalein, methyl orange.

Question 14.
Define ionisation.
Answer:
Ionisation is the condition of being dissociated into ions by heat or radiation or chemical reactions or electrical discharge.

Question 15.
How is normal salt obtained? Give a suitable reaction.
Answer:
A normal salt is obtained by complete neutralization of an acid by a base.
NaOH + HCl → NaCl + H₂O

Question 16.
How are bases classified based on ionisation?
Answer:
Based on Ionisation
(a) Strong Bases :
These are bases which ionise completely in aqueous solution.
Example: NaOH, KOH

(b) Weak Bases:
These are bases that ionise partially in aqueous solution.
Example: NH₄OH, Ca(OH)₂

VI. To Interpret:

Question 1.
CH₄ and NH₃, are not acids.
Answer:
CH₄ and NH₃ do not produce hydrogen ion (H⁺) in its aqueous solution.

Question 2.
Acetic acid (CH₃COOH) is a mono basic acid.
Answer:
Though acetic acid contains four hydrogen atoms only one hydrogen can be replaced in its aqueous solution. So CH₃COOH is a mono basic acid.
CH₃COOH → H⁺+ + CH₃COO^–

Question 3.
Al(OH)₃ & Zn(OH)₂ are not alkalis.
Answer:
Al(OH)₃ & Zn(OH)₂ are water insoluble bases. So they are bases not alkalies.

Question 4.
NaOH & KOH are strong bases.
Answer:
These are bases which ionise completely in aqueous solution.

Question 5.
NaHSO₄ is an acid salt.
Answer:
It is formed by the partial replacement of hydrogen ion of sulphuric acid (H₂ SO₄ ) by a metal present in sodium hydroxide (NaOH).
NaOH + H₂ SO₄ → NaHSO₄ + H₂O

Question 6.
Non-metallic oxides are acidic is nature.
Answer:
When non – metallic oxides react with bases, they can form a salt and water similar to the reaction of base with acids. So non-metallic oxides are acidic in nature.

VII. Complete the following table:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:
1. – d, 2. – f, 3. – a, 4. – e, 5. – c

Question 4.

Answer:
l.-e,2.-f,3.-d,4-b,5.-c

VIII. Find odd one out & give reason :

Question 1.
HCl, HNO₃, HCOOH, H₃PO₄
Answer:
H₃PO₄,
It is a tribasic acid whereas other three are monobasic acids.

Question 2.
Acetic acid, formic acid, tartaric acid, sulphuric acid.
Answer:
Sulphuric acid.
It is a mineral acid whereas other three are organic acids.

Question 3.
CaO, Na₂O, ZnO, NaOH
Answer:
NaOH.
It is a base containing replaceable hydroxyl ion. whereas other three bases contain replaceable oxide ions.

Question 4.
Bitter taste, soupy to touch, turns red litmus to blue, produce pink colour with methyl orange.
Answer:
Produce pink colour with methyl orange.
It is the property of acids whereas other three are properties of bases.

Question 5.
Litmus paper, phenolphthalein, methyl orange, Aquaregia.
Answer:
Aquaregia.
It is a mixture of two acids namely, hydrochloric acid and nitric acid, used to dissolve metals such as gold and platinum whereas other three are indicators used to identify the nature of the solution.

IX. Spot the error / Correct the wrong statement given below :

Question 1.
An acid is the compound which are capable of forming hydroxyl ions (OH^– ) in aqueous solution. .
Answer:
An acid is the compound which are capable of forming hydrogen ions (H+) in aqueous , solution, (or) A base is the compound which are capable of forming hydroxyl ion (OH-) in aqueous solution.

Question 2.
Nitric Acid is a constituent of baking powder.
Answer:
Tartaric acid is a constituent of baking powder.

Question 3.
The p^H value of the base in lesser than 7.
Answer:
The p^H value of the base is greater than 7. (or) p^H value of an acid is lesser than 7.

Question 4.
Ca(OH)₂ is a triacidic base.
Answer:
Ca(OH)₂ is a diacidic base (or) Al(OH)₃ is a triacidic base.

Question 5.
Magnesium hydroxide is used in whitewashing of buildings.
Answer:
Magnesium hydroxide is used as an antacid. (or) Calcium hydroxide is used in whitewashing of buildings.

X. Answer in detail :

Question 1.
Explain the classification of acids based on their basicity.
Answer:
Monobasic Acid :
Acid that contain only one replaceable hydrogen atom per molecule is called monobasic acid. It gives one hydrogen ion per molecule of the acid in solutions.
Example: HCl, HNO₃
.
Dibasic Acid :
An acid which gives two hydrogen ions per molecule of the acid in solution.
Example : H₂SO₄, H₂CO₃
‘
Tribasic Acid :
An acid which gives three hydrogen ions per molecule of the acid in solution.
Example: H₃PO₄.

Question 2.
Write notes on the properties of acids.
Answer:
(a) They have sour taste.
(b) Their aqueous solutions conduct electricity since they contain ions
(c) Acids turns blue litmus red.
(d) Acids react with active metals to give hydrogen gas.
Mg + H₂SO₄ → MgSO₄ + H ₂↑
Zn + 2HCl → ZnCl₂ + H₂↑

(e) Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑
NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

(f) Acids react with metallic oxides to give salt and water.
CaO + H₂SO₄ → CaSO₄+ H₂O

(g) Acids react with bases to give salt and water.
HCl + NaOH → NaCl + H₂O.

Question 3.
Write notes on the properties of bases. .
Answer:
(a) They have bitter taste.
(b) Their aqueous solutions have soapy touch.
(c) They turn red litmus blue.
(d)Their aqueous solutions conduct electricity.
(e) Bases react with metals to form salt with the liberation of hydrogen gas.
Zn + 2 NaOH → Na₂ZnO₂ + H₂↑

(f) Bases react with non-metallic oxides to produce salt and water. Since this is similar to the reaction between a base and an acid, we can conclude that non-metallic oxides are acidic in nature,
Ca(OH)₂ + CO₂ → CaCO₃+ H₂O

(g) Bases react with acids to form salt and water.
KOH + HCl → KCl + H₂O
The above reaction between a base and an acid is known as Neutralisation reaction.

(h) On heating with ammonium salts, bases give ammonia gas.
NaOH + NH₄Cl → NaCl + H₂O+ NH₃↑

Question 4.
Describe the classification of bases based on their acidity.
Answer:
(a) Monoacidic Base :
It is a base that ionises in water to give one hydroxide ion per molecule.
Example: NaOH, KOH

(b) Diacidic Base:
It is a base that ionises in water to give two hydroxide ions per molecule.
Example: Ca(OH)₂, Mg(OH)₂

(c) Triacidic Base :
It is a base that ionises in water to give three hydroxide ions per molecule.
Example: Al(OH)₃, Fe(OH)₃

Question 5.
Write notes on importance of pH in everyday life.
Answer:
p^H in our digestive system :
Hydrochloric acid produced in our stomach helps in the digestion of food without harming the stomach. During indigestion, the stomach produces too much acid and this causes pain and irritation. pH of stomach fluid is approximately 2.0

p^H changes is the cause of tooth decay :
White enamel coating of our teeth is calcium phosphate, the hardest substance in our body. Toothpaste which are generally basic and used for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

p^H of soil:
In agriculture, the pH of soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.

p^H of rain water:
The pH of rainwater is approximately 7 which means that it is neutral and also represents its high purity. If the atmospheric air is polluted with oxides of sulphur and nitrogen, they get dissolved in rainwater and make its pH less than 7. Thus, if the pH of rainwater is less than 7, then it is called acid rain. When acid rain flows into the rivers it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Question 6.
List the properties of salts.
Answer:

•  Salts are mostly solids which melt as well as boil at high temperature.
• Most of the salts are soluble in water.
  For example, chloride salts of potassium and sodium are soluble in water. But silver chloride is insoluble in water.
• They are odourless, mostly white, cubic crystals or crystalline powder with a salty taste.
• Salt is hygroscopic in nature.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 13 Chemical Bonding Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 13 Chemical Bonding

9th Science Guide Chemical Bonding Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Number of valence electrons in carbon is
(a) 2
(b) 4
(c) 3
(d) 5
Answer:
(b) 4

Question 2.
Sodium having atomic number 11, is ready to ______________ electron/electrons to attain the nearest noble gas electronic configuration.
(a) gain one
(b) gain two
(c) lose one
(d) lose two
Answer:
(c) lose one

Question 3.
The element that would form anion by gaining electrons in a chemical reaction is ………………..
(a) potassium
(b) calcium
(e) fluorine
(d) iron
Answer:
(c) fluorine

Question 4.
Bond formed between a metal and non metal atom is usually …………………..
(a) ionic bond
(b) covalent bond
(e) co-ordinate bond
Answer:
(a) ionic bond

Question 5.
______________ compounds have high melting and boiling points.
(a) Covalent
(b) Coordinate
(e) Ionic
Answer:
(c) Ionic

Question 6.
Covalent bond is formed by …………………
(a) transfer of electrons
(b) sharing of electrons
(c) sharing a pair of electrons
Answer:
(b) sharing of electrons

Question 7.
Oxidising agents are also called as …………………. because they remove eletrons form other substances.
(a) electron donors
(b) electron acceptors
Answer:
(b) electron acceptors

Question 8.
Elements with stable electronic configurations have eight electrons in their valence shell. They are ……………….
(a) halogens
(b) metals
(c) nobel gases
(d) non metals
Answer:
(c) noble gases

II. Answer briefly :

Question 1.
How do atoms attain Noble gas electronic configuration?
Answer:
Atoms of all elements, other than inert gases, combine to form molecules because they have incomplete valence shell and tend to attain a stable electronic configuration similar to noble gases. Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable outer shell of eight electrons.

Question 2.
NaCl is insoluble in carbon tetrachloride but soluble in water. Give reason.
Answer:
NaCl is an ionic compound, it is soluble in polar solvent (water). Whereas CCl₄ is a covalent compound. So.it is insoluble in polar solvent (water). But it is soluble in nonpolar solvents.

Question 3.
Explain the Octet rule with an example.
Answer:
The tendency of atoms to have eight electrons in the valence shell is known as the ‘Octet rule’ or the ‘Rule of eight’ For example, Sodium with atomic number 11 will readily loose one electron to attain Neon’s stable electronic configuration. Similarly, chlorine has electronic configuration 2,8,7. To get the nearest noble gas (i.e. Argon) configuration, it needs one more electron. So chlorine readily gains one electron from another atom and obtains stable electronic configuration. Thus elements tend to have stable valence shell (eight electrons) either by losing or gaining electrons.

Question 4.
Write a note on different types of bonds.
Answer:
There are different types of chemical bonding possible between atoms which make the molecules. Depending on the type of bond they show different characteristics or properties.

Question 5.
Correct the wrong statements.
(a) Ionic compounds dissolve in non-polar solvents.
(b) Covalent compounds conduct electricity in molten or solution state.
Answer:
(a) Covalent compounds dissolve in non-polar solvents. (or) Ionic compounds dissolve in polar solvents.
(b) Ionic compounds conduct electricity in molten or solution state.

Question 6.
Complete the table given below.

Answer:

Question 7.
Draw the electron distribution diagram for the formation of Carbon dioxide (CO₂) molecule.
Answer:

Question 8.
Fill in the following table according to the type of bonds formed in the given molecule.
CaCl₂, H₂O, CaO, CO, KBr, HCl, CCl₄, HF, CO₂, Al₂Cl₆

Answer:

Question 9.
The property which is characteristic of an Ionic compound is that
(a) it often exists as a gas at room temperature.
(b) it is hard and brittle.
(c) it undergoes molecular reactions
(d) it has a low melting point.
Answer:
(b) it is hard and brittle

Question 10.
Identify the following reactions as oxidation or reduction.
(a) Na → Na⁺ + e^–
(b) Fe³⁺ + 2 e^– → Fe⁺
Answer:
(a) oxidation
(b) reduction

Question 11.
Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics.
(a) Soluble in non-polar solvents
(b) Undergoes faster/instantaneous reactions
(c) Non-conductors of electricity
(d) Solids at room temperature
Answer:
(a) Co-ordinate Covalent compound.
(b) Ionic compound.
(c) Covalent compound.
(d) Ionic compound.

Question 12.
An atom X with atomic number 20 combines with atom Y with atomic number 8. Draw the dot structure for the formation of the molecule XY
Answer:

Question 13.
Considering MgCl₂ as ionic compound and CH₄ as covalent compound give any two differences between these two compounds.
Answer:

Question 14.
Why are Noble gases inert in nature?
Answer:
Noble gases are inert in nature due to the completely filled subshells and thus have stable electronic structures which is very difficult to change. The elements Helium, Neon, Argon, Krypton, Xenon and Radon of group 18 in the periodic table are Noble gases.

III. Answer in detail :

Question 1.
List down the differences between Ionic and Covalent compounds.
Answer:

Question 2.
Give an example for each of the following statements.
(a) A compound in which two Covalent bonds are formed.
(b) A compound in which one ionic bond is formed.
(c) A compound in which two Covalent and one Coordinate bond are formed.
(d) A Compound in which three covalent bonds are formed.
(e) A compound in which a coordinate bond is formed.
Answer:
(a) Oxygen molecule (O₂) (O = O)
(b) Sodium’Chloride (NaCl)
(c) Carbon monoxide?

(d) Nitrogen molecule (N₂) (N ≡N)
(e) NH₃ → BF₃

Question 3.
Identify the incorrect statement and correct them.
(a) Like covalent compounds, coordinate compounds also contain charged particles (ions). So they; are good conductors of electricity.
(b) Ionic bond is a weak bond when compared to Hydrogen bond.
(c) Ionic or electrovalent bonds are formed by the mutual sharing of electrons between atoms.
(d) Loss of electrons is called Oxidation and gain of the electron is called Reduction.
(e) The electrons which are not involved in bonding are called valence electrons.
Answer:
(a) Incorrect statement. Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(b) Incorrect statement. An ionic bond is a strong bond when compared to a hydrogen bond.
(c) Incorrect statement. Covalent bonds are formed by the mutual sharing of electrons between atoms, (or) Ionic or electrovalent bonds are formed by the transfer of electrons between atoms.
(d) Correct statement
(e) Incorrect statement. The electrons which are not involved in bonding are called lone pair of electrons.

Question 4.
Discuss in brief the properties of coordinate covalent compounds.
Answer:
The compounds containing coordinate covalent bonds are called coordinate compounds.
(a) Physical state – These compounds exist as gases, liquids or solids.
(b) Electrical conductivity-Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(c) Melting point – These compounds have to melt and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
(d) Solubility – Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCl₄, and toluene.
(e) Reactions – Co-ordinate covalent compounds undergo molecular reactions which are slow.

Question 5.
Find the oxidation number of the elements in the following compounds.
(a) C in CO₂
(b) Mn in MnSO₄
(c) N in HNO₃
Answer:
(a) C in CO₂
1(C) + 2(0) = 0
1x + 2(-2) = 0
x-4 = 0 ‘
x = +4 .
ON of C in CO₂ is +4

(b) Mn in MnSO₄
1 (Mn) + 1 (S) + 4(0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x – 2 = 0
x = +2
ON of Mn in MnSO₄ is +2,

(c) N in HNO₃
1(H) + 1 (N) +3(0) =0
1 (+1) + 1 (x) + 3 (-2) =0
+ 1 + x – 6 =0
x – 5 =0
x = +5
ON of N in HNO₃ is + 5.

9th Science Guide Chemical Bonding Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following atom can exist independently?
(a) Magnesium
(b) Chlorine
(c) Hydrogen
(d) Neon
Answer:
(d) Neon

Question 2.
Alkali and alkaline earth metals form ………… compound when they react with non-metals.
(a) ionic
(b) covalent
(c) co-ordinate covalent
(d) all the above
Answer:
(a) ionic

Question 3.
……………..compounds are highly brittle.
(a) Ionic
(b) Covalent
(c) Co-ordinate covalent
Answer:
(a) Ionic

Question 4.
The bond which is formed by mutual sharing of electrons is called ……………….. bond.
(a) ionic
(b) covalent
(c) co-ordinate covalent bond
(d) all the above
Answer:
(b) covalent

Question 5.
………………. is an example of a covalent compound having a high melting point.
(a) Magnesium oxide
(b) Silicon carbide
(c) Ammonia
(d) All the above
Answer:
(b) Silicon carbide

Question 6.
Which of the following compound(s) possesses a high melting point?
(a) NaCl
(b) MgCl₂
(c) CCl₄
(d) Both a & b
Answer:
(d) Both a & b

Question 7.
The element that would form cation due to the loss of electron during the chemical reaction is ………………..
(a) calcium
(b) Fluorine
(c) Chlorine
(d) all the above
Answer:
(a) calcium

Question 8.
Fajan’s rule is formulated by considering …………… the cation and ………………..of the cation and anion.
(a) charge
(b) size
(c) charge & size
(d) none
Answer:
(c) charge & size

Question 9.
The formation of brown colour on the freshly unit surface of vegetables and fruits is because ………………. of organic compounds present in them.
(a) oxidation
(b) reduction
(c) both a & b
(d) none
Answer:
(a) oxidation

Question 10.
Which of the following compounds has melting and boiling points higher than covalent compounds but lower than ionic compounds?
(a) NaCl
(b) MgCl₂
(c) H₂O
(d) NH₃→BF₃
Answer:
(d) NH₃→BF₃

Question 11.
Atoms having 1,2 or 3 electrons in their valence shell will readily form ……………..
(a) cation
(b) anion
Answer:
(a) cation

II. Fill in the blanks:

1. ……………theory explains the formation of molecules.
Answer:
Kossel – Lewis theory

The valency of noble gases is ……………..
Answer:
zero

3. …………….. is the only noble gas which does not have eight electrons in their valence shell.
Answer:
Helium

4. The atom that loses electrons will from a ________
Answer:
cation

5. ______ compounds have high density.
Answer:
Ionic

6. In covalent bond formation, the sharing of ………….. electrons takes place in their outermost shell.
Answer:
unpaired

7. Polar solvents contain bond between atoms with ………………
Answer:
different electronegativities

8. ……………….. & ………….. atoms have similar electronegativities.
Answer:
Carbon & hydrogen

9. Molecular reactions are ……………… in the covalent compound.
Answer:
slow

10. Ionic compounds are ……………..in nature.
Answer:
solid

11. The tendency of atoms to have eight electrons in the outer shell is known as ……………….
Answer:
Octet rule

12. As per Fajan’s rule, A1I₃is ……………..
Answer:
covalent

13. Oxidising agents are otherwise called as ………………..
Answer:
electron acceptors

14. The tarnishing of metals is due to the formation of ……………….
Answer:
metal oxide

15. The tarnishing of metals is an example of ……………. reaction.
Answer:
oxidation

16. The sum of oxidation number of all atoms in a compound is ………………..
Answer:
Zero

17. The ……………….. is a metal that has a high resistance to corrosion.
Answer:
Gold

III. Spot the error / correct the wrong statement:

Question 1.
In the formation of compounds, the inner shell electrons of an atom involved in bonding.
Answer:
In the formation of compounds, the valence electrons of an atom involved in bonding.

Question 2.
The atom that gains electrons will form a cation.
Answer:
The atom that gains electrons will form an anion.

Question 3.
Ionic compounds have low melting and boiling point.
Answer:
Ionic compounds have high melting and boiling point, (or) Covalent compounds have low melting and boiling point.

Question 4.
Non-polar solvents contain bonds between atoms with different electronegativities.
Answer:
Non-polar solvents contains bonds between atoms with similar electronegativities.

Question 5.
Covalent compounds are soluble in polar solvents.
Answer:
Covalent compounds are readily soluble in non-polar solvents, (or) Ionic compounds are soluble in polar solvents.

Question 6.
Greater the charge of the cation greater will be the ionic character.
Answer:
Greater the charge of the cation greater will be the covalent character.

IV. Match the following :

Question 1.

Answer:
1. – e, 2. – d, 3. – a, 4. – b, 5. – c

Question 2.

Answer:
1. – c, 2. – a, 3. – b, 4. – e, 5, – d.

V. Find the odd one out and write the reason:

Question 1.
Water, acetone, benzene, toluene turpentine.
Answer:
Water. It is a polar solvent where a^ others air non-polar solvents.

Question 2.
Addition of oxygen, removal of hydrogen, loss of an electron, gain of electron.
Answer:
Gain of electron. It is a reduction reaction whereas other three are oxidation reactions.

Question 3.
Platinum, palladium NaBH₄, CrO₃.
Answer:
CrO₃ It is an oxidising agent whereas the other three are reducing agents.

Question 4.
Ionic bond, metallic bond, Coordinate covalent bond, Hydrogen bond.
Answer:
Hydrogen bond. It is a weak bond whereas the other three are strong bonds.

Question 5.
Soft & waxy, a bad conductor of electricity, low boiling point, solid at room temperature.
Answer:
Solid at room temperature.
It is the property of ionic compounds whereas the other three are the properties of covalent compounds.

.
VI. Answer in brief :

Question 1.
What is a chemical bond?
Answer:
A chemical bond may be defined as the force of attraction between the two atoms that bind them together as a unit called a molecule.

Question 2.
Write the basic concept of Kossel – Lewis theory.
Answer:
Kossle – Lewis theory is based on the concept of electronic configuration of noble gases.

Question 3.
Define the ionic bond.
Answer:
An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions. The bond is formed between two atoms when one or more electrons are transferred from the valence shell of one atom to the valence shell of the other atom.

Question 4.
The following shows the electronic distribution diagram for the formation of MgCl₂ molecule. Based on this answer the following questions.

(a) Which of the above atom loses electrons to form a cation?
(b) Which of the above atom gain electrons to form an anion?
(c) How many electrons are transferred from Mg to Cl?
(d) Write the name of the anion formed.
(e) Which noble gas configuration do these ions resemble?
(f) Write the electronic configuration of Mg²⁺ & Cl^–
Answer:
(a) Magnesium atom loses electrons to form a cation.
(b) Chlorine atom gains 1 electron to from anion.
(c) Two electrons are transferred from Mg – atom to 2 Cl – atoms (each Cl – atom gains 1e^– from Mg – atom).
(d) Chloride anion (Cl^– )
(e) Mg²⁺ ion resembles noble gas configuration of Neon Cl^– ion resembles noble gas configuration of Argon.
(f) Electronic configuration of Mg²⁺ is 2, 8. and Electronic configuration of Cl^– is 2, 8, 8.

Question 5.
What is covalent bond?
Answer:
Bond which is formed between atoms by the mutual sharing of electrons is known as a covalent bond.

Question 6.
Name of the following:
(a) An element which obtains the noble gas configuration of neon by losing three electrons.
(b) An element which gains two electrons to obtain the noble gas configuration of Neon.
Answer:
(a) Aluminium (Al → Al³⁺ + 3e^–)
(b) Oxygen atom (O + 2e^– → 0^2-)

Question 7.
Identify the following reactions as oxidation/reduction/redox reaction.
(a) Zn + CuSO₄ → Cu + ZnSO₄
(b) CuO+H₂ → Cu+H₂O
(c) 2Mg +O₂  → 2MgO
Answer:
(a) Redox reaction
(b) Reduction
(e) Oxidation

Question 8.
What are oxidising agents? Give an example.
Answer:
Substances which have the ability to oxidise other substances are called oxidizing agents. These are also called electron acceptors because they remove electrons from other substances. ’
Example:

Question 9.
What are reducing agents? Give examples.
Answer:
Substances which have the ability to reduce other substances are called reducing agents. These are also called electron donors because they donate electrons to other substances.
Example: NaBH₄, LiAlH₄ and metals like Palladium, Platinum.

Question 10.
What are redox reactions? Give examples.
Answer:
Both the oxidation and reduction occurs in the same reaction simultaneously is known as a redox reaction. If one reactant gets oxidised, the other gets reduced. Such reactions are called oxidation-reduction reactions or redox reactions.
Ex. 1 : 2 PbO + C → 2 Pb + CO₂
Ex. 2 : Zn + CuSO₄  → Cu + ZnSO₄

Question 11.
Define (a) oxidation (b) reduction reactions : Give examples.
Answer:

Question 12.
What is rancidity?
Answer:
The oxidation reaction in food materials that were left open for a long period is responsible for spoiling of food. This is called rancidity.

Question 13.
Define oxidation number.
Answer:
Oxidation number of an element is defined as the formal charge which an atom of that element appears to have when electrons are counted.

Question 14.
Identify the type of bond in \(\mathrm{NH}_{4}^{+}\)

Answer:

VII. To interpret:

Question 1.
Ionic bond is also called electrostatic bond.
Answer:
In ionic bond formation the bond is formed between the oppositely charged ions and these ions come closer to each other due to electrostatic force of attraction. So ionic bond is also called an electrostatic bond.

Question 2.
Ionic compounds are crystalline solids at room temperature.
Answer:
Ionic compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

Question 3.
Covalent compounds have a low melting point.
Answer:
In covalent compounds, atoms are held by a weak force of attraction. When heat is applied, the molecules are readily pulled out and get free movement.

VIII. Assertion and Reason type questions :

Question 1.
Statement (A) : Ionic compounds do not conduct electricity in a solid-state.
Reason (B) : The ions in ionic compounds are tightly held together by a strong electrostatic force of attraction and they can not move freely.
(a) B explains A
(b) B does not explain A
(c) B is wrong A
(d) A is right B is wrong
Answer:
(a) B explains A

Question 2.
Statement (A) : Covalent compounds are bad conductors of electricity.
Reason (B) : Covalent compounds contain charged particles (ions)
a) B explains A
b) B does not explain A
c) Both A & B are right
d) Both A & B are wrong
Answer:
(b) B does not explain A
Reason: Since covalent compounds do not have charged particles (ions), they are bad conductors of electricity.

IX. Find the oxidation number of the elements in the following compounds.

(1) Zn in ZnSO₄
(2) Ca in CaH₂
(3) Mg in MgO
(4) N in NH₃
(5) A1 in AlCl₃
Answer:
(1) ZnSO₄
1(Zn) + 1 (S) + 4 (0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x = + 2
Oxidation number of Zn in ZnSO₄ is +2

(2) CaH₂
1(Ca) + 2 (H) = 0
x + 2 (-1) = 0
x -2 = 0
x = + 2
Oxidation number of Ca in CaH₂ is +2

(3) MgO
1(Mg) + 1 (O) = 0
x + 1 (-2) = 0
x -2 = 0
x = + 2
Oxidation number of Mg in MgO is +2

(4) NH₃
1(N) + 3 (H) = 0
x + 3 (-1) = 0
x – 3 = 0
x = +3
Oxidation number of N in NH₃ is +3
(5) AlCl₃
1(Al) + 3(Cl) = 0
x + 3 (-1) = 0
x – 3 = 0
x = + 3
Oxidation number of Al in AlCl₃ is +3

X. Complete the following table:

Question 1.

Answer:

Question 2.

Answer:

XI. To Match:

Answer:

XII. Answer in detail :

Question 1.
Explain the ionic bond formation in sodium chloride with electron distribution diagram.
Answer:
Formation of Sodium Chloride (NaCl)

(i) The atomic number of Sodium is 11 and its electronic configuration is 2, 8, 1. It has one electron excess to the nearest stable electronic configuration of a noble gas – Neon.

(ii) So sodium has a tendency to lose one electron from its outermost shell and acquire a stable electronic configuration forming sodium cation (Na⁺).

(iii) The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. It has one electron less to The nearest stable electronic configuration of a noble gas – Argon.

(iv) So chlorine has a tendency to gain one electron to acquire a stable electronic
configuration forming chloride anion (Cl^–)

(v) When an atom of sodium combines with an atom of chlorine, an electron is transferred from the sodium atom to chlorine atom forming sodium chloride molecule. Thus both the atoms achieve stable octet electronic configuration.

Question 2.
Explain the covalent bond formation in the following molecules.
(a) Chlorine
(b) Nitrogen
(c) Hydrogen
(d) Oxygen
Answer:
(a) Chlorine
Chlorine molecule is formed by two chlorine atoms. Each chlorine atom has seven valence electrons (2,8,7). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing a pair of electrons.

(b) Nitrogen
Nitrogen molecule is formed by two nitrogen atoms. Each nitrogen atom has five valence electrons (2, 5). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing three pair of electrons. Hence a triple bond is formed in between the two atoms.

(c)Hydrogen
Hydrogen molecule is formed by two hydrogen atoms. Both hydrogen atoms contributes one electron each to the shared pair and both atoms acquire stable completely filled electronic configuration.

(d) Oxygen
Oxygen molecule is formed by two oxygen atoms. Each oxygen atom has six valence electrons (2,6). These two atoms achieve a stable electronic configuration (octet) by sharing two pair of electrons. Hence a double bond is formed in between
the two atoms.

Question 3.
Explain the co-ordinate covalent bond formation in between NH₃ → BF₃ molecules.
Answer:
The ammonia molecule gives a lone pair of electrons to boron trifluoride (BF₃) molecule which is electron deficient. Thus a coordinate covalent bond is formed between NH₃ (donor molecule) and BF₃ (acceptor molecule) and is represented by

Question 4.
Write notes on the characteristics of covalent compounds.
Answer:
a. Physical state: Depending on the force of attraction between covalent molecules the bond may be weaker or stronger. Thus covalent compounds exist in gaseous, liquid, and solid forms. Eg. Oxygen-gas; Water-liquid: Diamond-solid.

b. Electrical conductivity: Covalent compounds do not contain charged particles (ions), so they are bad conductors of electricity.

c. Melting point: Except few covalent compounds (Diamond, Silicon carbide), they have relatively low melting points compared to Ionic compounds.

d. Solubility: Covalent compounds are readily soluble in non-polar solvents like benzene (C₆H₆), carbon tetrachloride (CCl₄). They are insoluble in polar solvents like water.

e. Hardness and brittleness: Covalent compounds are neither hard nor brittle. But they are soft and waxy.

f. Reactions: Covalent compounds undergo molecular reactions in solutions and these reactions are slow.

Question 5.
Write notes on the characteristics of ionic compounds.
Answer:
a. Physical state: These compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

b. Electrical conductivity: Ionic compounds are crystalline solids and so their ions are tightly held together. The ions, therefore, cannot move freely, so they do not conduct electricity in a solid-state. However, in a molten state and their aqueous solutions conduct electricity.

c. Melting point: the strong electrostatic force between the cations and anions hold the ions tightly together, so very high energy is required to separate them. Hence ionic compounds have high melting and boiling points.

d. Solubility: Ionic compounds are soluble in polar solvents like water. They are insoluble in non-polar solvents like benzene (C₆H₆), carbon tetrachloride (CCl₄).

e. Density, hardness, and brittleness: Ionic compounds have high density and they are quite hard because of the strong electrostatic force between the ions. But they are highly brittle.

f. Reactions: Ionic compounds undergo ionic reactions which are practically rapid and instantaneous.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 12 Periodic Classification of Elements Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 12 Periodic Classification of Elements

9th Science Guide Periodic Classification of Elements Text Book Back Questions and Answers

I. Choose the correct answer :
Question 1.
If Dobereiner is related with ‘law of triads’, then Newlands is related with
(a) Modem periodic law
(b) Hund’s rule
(c) Law of octaves
(d) Pauli’s Exclusion principle
Answer:
(c) law of octaves

Question 2.
Modern periodic law states that the physical and chemical properties of elements are the periodic functions of their ……………
(a) atomic numbers
(b) atomic masses
(c) similarities
(d) anomalies
Answer:
(a) atomic numbers

Question 3.
Elements in the modern periodic table are arranged in …………. groups and ………….. periods .
(a) 7, 18
(b) 18,7
(c) 17,8
(d) 8, 17
Answer:
(b) 18, 7

Fill in the blanks:

1. In Dobereiner’s triads, the atomic weight of the middle element is the __________ of the atomic masses of 1 and 3rd elements.
Answer:
average

2. Noble gases belong to ___________ group of the periodic table.
Answer:
18th

3. The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was ……………….
Answer:
atomic mass

4. Example for liquid metal is ______________ .
Answer:
mercury

III. Match the following:
Question

Answer:

IV. State whether true or false. If false, correct the statement:

Question 1.
Newlands’ periodic table is based on atomic masses of elements and modem periodic table is based on atomic number of elements.
Answer:
True.

Question 2.
Metals can gain electrons.
Answer:
False.
Correct statement: Metals tend to lose electrons.

Question 3.
Alloys bear the characteristics of both metals and nonmetals.
Answer:
False.
Correct statement: Metalloids bear the characteristics of both metals and nonmetals.

Question 4.
Lanthanides and actinides are kept at the bottom of the periodic table because they resemble each other but they do not resemble with any other group elements.
Answer:
True.

Question 5.
Group 17 elements are named as Halogens.
Answer:
True.

V. Assertion and Reason :

Question
Statement : Elements in a group generally possess similar properties but elements along a period have different properties.
Reason : The difference in electronic configuration makes the element differ in their chemical properties along a period.
a) Statement is true and reason explains the statement.
b) Statement is false but the reason is correct.
Answer:
(a) Statement is true and reason explains the statement

VI. Answer the following :

Question 1.
State modern periodic law.
Answer:
The modem periodic law states that:
“The Chemical and Physical properties of elements are periodic functions of their atomic numbers”.

Question 2.
What are groups and periods in the modern periodic table?
Answer:

•  The horizontal rows in the periodic table are called periods.
• Vertical columns in the periodic table starting from top to bottom are called groups.

Question 3.
What are the limitations of Mendeleev’s periodic table?
Answer:

• Elements with large differences in properties were included in the same group. Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).
• No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).
• The increasing order of atomic mass was not strictly followed throughout. Eg. Co & Ni, Te &I.
• No place for isotopes in the periodic table.

Question 4.
State any five features of the modern periodic table.
Answer:

• All the elements are arranged in the increasing order of their atomic number.
• The horizontal rows are called periods. There are seven periods in the periodic table.
• The elements are placed in periods based on the number of shells in their atoms.
• Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
• Based on the physical and chemical properties of elements, they are grouped into various families.

Intext Activities

ACTIVITY -1

Find the pair of elements having similar properties by applying Newlands’ law of Octaves
(Example: Mg & Ca):
Set I : F, Mg, C, O,B
Set II: Al, Si, S, Cl, Ca
Answer:

1. F-Cl
2. Mg-Ca
3. C-Si
4. O-S
5. B-Al

9th Science Guide Periodic Classification of Elements Additional Important Questions and Answers

Choose the correct answer:

Question 1.
Noble gases are placed in the _______ group in the modern periodic table.
(a) 13th
(b) 18th
(c) 17th
(d) 2nd
Answer:
(b) l8th

Question 2.
Group 16 elements are collectively called as _______ .
(a) chalcogen family
(b) carbon family
(e) halogens
(d) nitrogen family
Answer:
(a) chalcogen family

Question 3.
The maximum number of electrons that can be accommodated in s, p ,d, and f subshells are _________ .
(a) 14, 10, 6, 2
(b) 6, 10, 2, 14
(c) 2, 6, 10, 14
(d) 6, 2, 14, 10
Answer:
c) 2, 6, 10, 14

Question 4.
d-block elements are otherwise known as _________ .
(a) transition elements
(b) inner transition elements
(c) halogens
(d) alkali metals
Answer:
(a) transition elements

Question 5.
Which block of the periodic table contains metals, non-metals and metalloids?
(a) s
(b) p
(c) d
(d) f
Answer:
(b) p

Question 6.
Which of the following non-metals can form alloys with metals?
(a) Boron
(b) Carbon
(c) Silicon
(d) All the above
Answer:
(d) all the above

Question 7.
Which of the following metals have low melting and boiling point?
(a) Sodium :
(b) Potassium
(e) Iroñ
(d) Both a & b
Answer:
(d) Both a & b

Question 8.
Which of the following metal (s) do not react with water?
(a) Gold
(b) Silver
(c) Copper
(d) All the above
Answer:
(d) All the above

Question 9.
If the electronic configuration of an element is 1s² 2s² 2p⁶ 3s² 3p¹’then it will
occupy ……………… block of the periodic table.
(a) s
(b) p
(c) d
(d) f
Answer:
(b) p

II. Fill in the blanks :

1. ……………… group elements are called alkaline earth metals.
Answer:
Second

2. The elements that follow lanthanum are called ……………..
Answer:
Lanthanides

3. f-block elements are also known as …………………..
Answer:
inner transition elements

4. …………… block element is placed at the bottom of the periodic table.
Answer:
f-

5. The mixture of metal with mercury is called …………………..
Answer:
amalgam

6. Elements are placed in periods based on the number of ……………… in their atoms.
Answer:
shells

III. Spot the error :

Question 1.
The elements of group 13 are called the carbon family.
Answer:
The elements of group 13 are called boron family
(or)
The elements of group 14 are called the carbon family.

Question 2.
There are 5 periods and 17 groups in the modern periodic table.
Answer:
There are 7 periods and 18 groups in the modem periodic table.

IV. Pick the odd one out and write the reason:

Question 1.
Copper, brass, gold ornament, bronze.
Answer:
Copper.
Copper is metal whereas the other three are alloys.

Question 2.
Bromine, carbon, hydrogen, aluminium.
Answer:
Aluminium.
Aluminium is metal whereas the other three are non-metals.

V. To match :

Answer:
a) alkali metals
b) 3 to 12
c) 13
d) Nitrogen family
e) halogens

VI. Answer in brief :

Question 1.
What are the s-block elements?
Answer:
Elements whose valence electron is filled in s subshell is known as s-block elements.

Question 2.
What are the p-block elements?
Answer:
The last electron in these elements is filled in p subshells and hence these elements are called p block elements. These elements are in group 13 to 18 in the periodic table.

Question 3.
What are alloys?
Answer:
Alloys are mixtures of two or more metals and are formed by mixing molten metals thoroughly. Rarely nonmetals are also mixed with metals to produce alloys.

Question 4.
What are metalloids? Give examples.
Answer:
Elements which have the properties of both metals and non-metals are called as metalloids, (eg) Boron, Arsenic.

Question 5.
State Mendeleev’s Law of Periodicity.
Answer:
The physical and chemical properties of elements are the periodic functions of their atomic masses.

Question 6.
State Newlands’ Law of Octaves.
Answer:
Every eighth element had properties similar to those of the first element like the eighth note in an octave of music is similar to the first.

Question 7.
An element has atomic number 12.
a) Write the electric configuration.
b)To which group and period do it belong.
Answer:
a) K = 2, L = 8, M = 2
b) Group No . 2, Period No. 3

Question 8.
Relate the names of the following scientists with the statements given below. (Mendeleev, Newlands, Dobereiner).
a) Arranged elements into groups containing three elements each.
b) Arranged elements in a group of seven with increasing atomic masses and eighth elements with similar properties kept below the first like eight note in an act of music.
c) Arranged elements in the increasing order of atomic mass
Answer:
a) Dobereiner
b) Newlands
c) Mendeleev

Question 9.
Complete the following triads by inserting the missing elements.
a) Cl, ………., I
b) Li, ………, K
c) Ca, …………, Ba
Answer:
a) Br
b) Na
c) Sr

Question 10.
How are elements grouped into various families in the periodic table?
Answer:
Based on the physical and chemical properties of elements, they are grouped into various families.

VII. To interpret:

Question 1.
Group 1 (except hydrogen) elements are called alkali metals.
Answer:
The elements of group 1 (except hydrogen) are metals. They react with water to form solutions that change the colour of a vegetable dye from red to blue. These solutions are said to be highly alkaline or basic. Hence they are called alkali metals.

Question 2.
d-block elements are called transition elements.
Answer:
d-block elements are found in the centre of the periodic table. Their properties are intermediate to that of s block and p block elements and so they are called transition elements.

Question 3.
Group 3-12 elements in the modern periodic table are called d block elements.
Answer:
The elements of group 3 to 12 have their valence electrons in their outermost d subshells. These elements are called d block elements.

VIII. Complete the following table :

Question

Answer:
1) 2
2) 10
3) 18
4) 2,8,1

IX. Assertion and Reason :

Question 1.
Assertion (A): Group 2 elements in the modem periodic table are called alkaline earth metals.
Reason (R): The oxides of group 2 elements produce alkaline solutions when they are dissolved in water.
(a) A is right R is wrong
(b) R explains A
(c) R does not explain A
(d) R is right A is wrong
Answer:
(b) R explains A

Question 2.
(A) : Noble gases are chemically inert in nature.
Reason (R) : Noble gases have stable electronic structures.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is wrong R is right
Answer:
(a) Both A & R are right]

Question 3.
Assertion (A): Non-metals are electronegative.
Reason (R) : Non-metal losë electrons to form cation.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is the wrong R is right
Answer:
(c) A is right R is wrong

X. Long answer type questions:

Question 1.
List the advantages of alloys.
Answer:

• Alloys do not get corroded or get corroded to a very less extent.
• They are harder and str9ner than pure metals (Example: Gold is mixed with copper and it is harder than pure gold)
• They have less conductance than pure metals (Example: Copper is a good conductor of heat and electricity whereas brass and bronze are not good conductors)
• Some alloys have lower melting point than pure metals (Example: Solder is an alloy of lead and tin which has a lower melting point thàn each of the metals)
• When metal is alloyed with mercury, it is called amalgam.

Question 2.
Write the advantages of the Modern Periodic Table.
Answer:

• The table is based on a more fundamental property i.e., atomic number.
• It correlates the position of the element with its electronic configuration more clearly.
• The completion of each peçiod is more logical. In a period, as the atomic number increases, the energy shells are gradually filled up until an inert gas configuration is reached.
• It is easy to remember and reproduce.
• Each group is an independent group and the idea of subgroups has been discarded.
• One position for all isotopes of an element is justified since the isotopes have the same atomic number.
• The position of the eighth group (in Mendeleev’s table) is also justified in this table. All transition elements have been brought in the middle as the properties of transition elements are intermediate between the left portion and right portion elements of the periodic table.
• The table completely separates metals from nonmetals. The nonmetals are present in the upper right corners of the periodic table.
• The positions of certain elements which were earlier misfit (interchanged) in Mendeleev’s periodic table are now justified because it is based on an atomic number of the elements.
• Justification has been offered for placing lanthanides and actinides at the bottom of the periodic table.

Question 3.
Explain the position of hydrogen in the periodic table.
Answer:
Hydrogen is the lightest, smallest and first element of the periodic table. Its electronic configuration (1s¹) is the simplest of all the elements. It occupies a unique position in the periodic table. It behaves like alkali metals as well as halogens in its properties. In the periodic table, it is placed at the top of the alkali metals.

• Hydrogen can lose its one electron to form a hydrogen ion (H⁺) like alkali metals.
• It can also gain one electron to form the hydride ion (H^–) like halogens.
• Alkali metals are solids while hydrogen is a gas.
  Hence the position of hydrogen in the modem periodic table is still under debate
  as the properties of hydrogen are unique.

Question 4.
List the features of Mendeleev’s Periodic Table.
Answer:
1. It has eight vertical columns called ‘groups’ and seven horizontal rows called ‘period’.

2. Each group has two subgroups ‘A’ and ‘B’. All the elements appearing in a group were found to have similar properties.

3. For the first time,-elements were comprehensively classified in such a way that elements of similar properties were placed in the same group.

4. It was noticed that certain elements could not be placed in their proper groups in this manner. The reason for this was wrongly determined atomic masses, and consequently those wrong atomic masses were corrected. Eg: The atomic mass of beryllium was known to be 14. Mendeleev reassessed it as 9 and assigned beryllium a proper place;

5. Columns were left vacant for elements which were not known at that time and their properties also were predicted. This gave me the motivation to experiment in Chemistry. Eg: Mendeleev gave the names Eka Aluminium and Eka Silicon to those elements which were to be placed below aluminium and silicon respectively in the periodic table and predicted their properties. The discovery of Germanium later on, during his lifetime, proved him correct.

Properties of Germanium:

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 9 Universe Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

9th Science Guide Universe Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Who proposed the heliocentric model of the universe?
(a) Tycho Brahe
(b) Nicolaus Copernicus
(c) Ptolemy
(d) Archimedes
Answer:
(b) Nicolaus Copernicus

Question 2.
Which of the following is not a part of outer solar system?
(a) Mercury
(b) Saturn
(c) Uranus
(d) Neptune
Answer:
(a) Mercury

Question 3.
Ceres is a …………….
(a) Meteor
(b) Star
(e) Planet
(d) Asteroid
Answer:
(d) Asteroid

Question 4.
The period of revolution of planet A around the Sun is 8 times that of planet B. How many times is the distance of planet A as great as that of planet B?
(a) 4
(b) 5
(e) 2
(d) 3
Answer:
(a) 4

Question 5.
The Big Bang occurred _____ years ago.
(a) 13.7 billion
(b) 15 million
(e) 15 billion
(d) 20 million
Answer:
(a) 13.7 billion

II. Fill in the blanks :

1. The speed of Sun in km/s is ………………
Answer:
250 km/s

2. The rotational period of the Sun near its poles is ………………
Answer:
36 days

3. India’s first satellite is ……………..
Answer:
Aryabhatta

4. The third law of Kepler is also known as the Law of ……………….
Answer:
Harmonics

5. The number of planets in our Solar System is …………………
Answer:
8

III. State whether true or false. If false, correct the statement:

1. ISS is a proof for international cooperation.
Answer:
True.

2. Halley’s comet appears after hearly 67 hours.
Answer:
False.
Correct statement: Halley’s comet appears after nearly 76 years.

3. Satellites nearer to the Earth should have lesser orbital velocity.
Answer:
False.
Correct statement: Satellites nearer to the Earth should have faster orbital velocity.

4. Mars is called the red planet.
Answer:
True.

IV. Answer briefly :

Question 1.
What is the solar system?
Answer:
The Sun and celestial bodies which revolve around it form the solar system. It consists of a large number of bodies such as planets, comets, asteroids, and meteors.

Question 2.
Define orbital velocity.
Answer:
The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called “orbital velocity”.

Question 3.
Define time period of a satellite.
Answer:
Time taken by the satellite to complete one revolution around the Earth is called the time period.
Time period, T = Distance covered/Orbital velocity
T = 2πr/v

Question 4.
What is the satellite? What are the two types of satellites?
Answer:
A body moving in orbit around a planet is called a satellite.
The two types of Satellites are

1.  Natural satellites,
2.  Man-made satellites.

Question 5.
Write a note on the inner planets.
Answer:
The planets are spaced unevenly. The first four planets are relatively close together and close to the Sun. They form the inner solar system. The four planets grouped together in the inner solar system are Mercury, Venus, Earth, and Mars. They are called inner planets. They have a surface of solid rock crust and so are called terrestrial or rocky planets. Their insides, surfaces, and atmospheres are formed in a similar way and form a similar pattern. Our planet, Earth can be taken as a model of the other three planets.

Question 6.
Write about comets.
Answer:

• Comets are lumps of dust and ice that revolve around the Sim in highly elliptical orbits.
• Their period of revolution is very long.
• Comet vapourises and forms a head and tail on approaching the sun.
• Tail of the biggest comet may be around 160 million km.
• There are period comets (e:g) Halley’s comet which appears after every 76 years.

Question 7.
State Kepler’s laws.
Answer:
In the early 1600s, Johannes Kepler proposed three laws of planetary motion.
First Law – The Law of Ellipses
The path of the planets about the Sun is elliptical in shape, with the center of the Sun being located at one of the foci.

Second Law – The Law of Equal Areas
An imaginary line drawn from the center of the Sun to the center of the planet will sweep out equal areas in equal intervals of time.

Third Law – The Law of Harmonies
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their semi-major axis from the Sun.

Question 8.
What factors have made life on Earth possible?
Answer:
Factors responsible for life on Earth.

1. Right distance from the Sun.
2. Right temperature.
3. Presence of water.
4. Suitable atmosphere.
5. Blanket of ozone.

V. Answer in detail:

Question 1.
Give an account of all the planets in the solar system.
Answer:

The planets are spaced unevenly. The first four planets are relatively close together and close to the Sun. They form the inner solar system. Farther from the Sun is the outer solar system, where the planets are much more spread out. Thus the distance between Saturn and Uranus is much greater (about 20 times) than between the Earth and Mars.

The four planets grouped together in the inner solar system are Mercury, Venus, Earth, and Mars. They are called inner planets. They have a surface of solid rock crust and so are called terrestrial or rocky planets. Their insides, surfaces, and atmospheres are formed in a similar way and form a similar pattern. Our planet, Earth can be taken as a model of the other three planets.

The four large planets Jupiter, Saturn, Uranus and Neptune spread out in the outer solar system that slowly orbits the Sun are called outer planets. They are made of hydrogen, helium and other gases in huge amounts and have very dense atmosphere. They are known as gas giants and are called gaseous planets. The four outer planets Jupiter, Saturn, Uranus and Neptune have rings whereas the four inner planets do not have any rings. The rings are actually tiny pieces of rock covered with ice.

Question 2.
Discuss the benefits of ISS.
Answer:

1. Water purification efforts :
The water recovery system (WRS) and the oxygen generation system (OGS) techniques developed by ISS provides advanced water Alteration and purification to water scarcity areas

2. Eye-tracking technology :
Eye-tracking technology can be used in many laser surgeries which tracks eye’s position very accurately and helps the disabled people with limited movement and speech.

3. Robotic arms and Surgeries :
Robotic arms provide significant help to surgeons in removing inoperable tumours and taking biopsies with great accuracies.

4. Apart from the above, there are many other applications such as the development of improved vaccines, breast cancer detection and treatment, and so on.

Question 3.
Write a note on orbital velocity.
Answer:
Nowadays many artificial satellites are launched into the Earth’s orbit. The first artificial satellite Sputnik was launched in 1956. India launched its first satellite Aryabhatta on April 19, 1975. Artificial satellites are made to revolve in an orbit at a height of a few hundred kilometres. At this altitude, the friction due to air is negligible. The satellite is carried by rocket to the desired height and released horizontally with a high velocity so that it remains moving in a nearly circular orbit. The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called orbital velocity.

The orbital velocity of the satellite depends on its altitude above Earth. The nearer the object to the Earth, the faster is the required orbital velocity. At an altitude of 200 kilometres, the required orbital velocity is a little more than 27,400 kph. That orbital speed and distance permit the satellite to make one revolution in 24 hours. Since Earth also rotates once in 24 hours, a satellite stays in a fixed position relative to a point on Earth’s surface. Because the satellite stays over the same spot all the time, this kind of orbit is called ‘geostationary’.

Orbital velocity can be calculated using the following formula.
v = \(\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+\mathrm{h})}}\)
where; G = Gravitational constant (6.673 × 10^{– 11}Nm²kg^{– 2})
M = Mass of the Earth (5.972 × 10²⁴kg)
R = Radius of the Earth (6371 km)
h = Height of the satellite from the surface of the Earth.

VI. Conceptual Questions

Question 1.
Why do some stars appear blue and some red?
Answer:

1. Stars appear in different colours depending on their temperatures.
2. Hot stars are white or blue in colour.
3. Cooler stars are orange or red in colour.

Question 2.
How is a satellite maintained in nearly circular orbit?
Answer:
Artificial satellites are made to revolve in an orbit at a height of a few hundred kilometres. At this altitude, the friction due to air is negligible. The satellite is carried by rocket to the desired height and released horizontally with a high velocity so that it remains moving in a nearly circular orbit.

Question 3.
Why are some satellites called geostationary?
Answer:
The Earth rotates once in 24 hours, a satellite stays in a fixed position.
Because the satellite stays over the same spot all the time, this kind of orbit is called . “geostationary”.

Question 4.
A man weighing 60 kg on the Earth will weigh 1680 kg in the Sun. Why?
Answer:
Mass of the man = 60Kg
w = m × g
m = 60Kg, g = 274.13m/s²
The sun’s gravitational acceleration is 30 times more than that of the earth. So the person would weigh 16,447N on the surface of the sun.

VII. Numerical Problems

Question 1.
Calculate the speed with which a satellite moves if it is at a height of 36,000 km from the Earth’s surface and has an orbital period of 24 hr (Take R = 6370 km).
[Hint: Convert hr into seconds before doing the calculation)

Solution:
Given:
Height of the satellite, h = 36,000 km = (36,000) ×10³m
Radius of the Earth, R = 6370 km = (6370) × 10³m
We know: Gravitational constant, G = 6.673 10^-11Nm²kg^-2
Mass of the Earth, M = 5.972 × 10²⁴kg.

Orbital velocity, v = 3.067×10 ³ m/s (or) 3067m/s (or) 3.067 km/s.

Question 2.
At an orbital height of 400 km, find the orbital period of the satellite.
Solution : Given : Orbital height, h = 400 km = 400 × 10³m
We know : Gravitational constant, G = 6.673 × 10^-11Nm²kg^-2
Mass of the earth, M =5.972 ×10²⁴kg
Radius of the Earth, R = 6371 km = 6371 × 10^-3m.

Intext Activities

ACTIVITY – 1

Form a team of three to four students. Prepare a poster about the astronomers

ACTIVITY – 2

Observe the sky keenly during night. Can you see group of stars? Can you figure out any shape? Discuss with your teachers and find out their name.
Aim : To observe the group of stars in the night sky.

Procedure :

1. Observe the night sky keenly.
2. Observe the movements of stars
3. Imagine the shapes

Observation :
By discussing with the teachers following groups are identified.

ACTIVITY – 3

Watch the sky in the early morning. Do you see any planet? What is its name? Find out with the help of your teachers.
Aim :
1. Most of the planets cannot be seen in normal sky.
2. Few planets can be seen during some specific period in the night sky.
3. Mercury, closest to the sun can be seen from the earth.
4. Venus is also seen few days in a year.
5. Uranus may be also seen on odd days in October.

ACTIVITY – 4

Prepare a list of Indian satellites from Aryabhatta to the latest along with their purposes.
S.No. Name of satellite Year Purpose
s

9th Science Guide Universe Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
The Geocentric model of universe was proposed by ……………
(a) Tyago Brane
(b) Kepler
(c ) Ptolemy
(d) Copernicus
Answer:
ptolemy

Question 2.
The total area of observable universe is about light-years.
(a) 9.3 billion
(b) 93 billion
(c) 93 million
(d) 9.3 million
Answer:
93 billion

Question 3.
All the atoms together only make up ______ percent of universe.
(a) 3
(b) 4
(c) 5
(d) 2
Answer:
(b) 4

Question 4.
The milky way galaxy is ………………in shape.
(a) Elliptical
(b) Circular
(e) Spiral
(d) Irregular
Answer:
(c) spiral

Question 5.
Stars are built by ____ gases.
(a) Hydrogen
(b) Helium
(e) Nitrogen
(d) Oxygen
Answer:
(a) Hydrogen

Question 6.
The process that takes place in the Sun is ………………
(a) Nuclear Fission
(b) Spallation
(c) Nuclear Fusion
(d) None of these
Answer:(c)
Nuclear Fusion
Question 7.
The energy of the sun is radiated in the form of_____ Rays.
(a) Ultraviolet
(b) Infrared
(e) neutron radiation
(d) X-rays
Answer:
(b) Infrared

Question 8.
The ____ colour is the most intense colour in solar radiation.
(a) blue
(b) red
c) violet
(d) yellow
Answer:
(d) yellow

Question 9.
Athe distance of the planet from the sun increases, the period of revolution ………………..
(a) increases
b) decreases
(c) remains the same
(d) a & b
Answer:
(a) increases

Question 10.
Which among the planets has less length of a day?
(a) Mercury
(b) Uranus
(c) Jupiter
(d) Saturn
Answer:
(c) Jupiter

Question 11.
The hottest planet on the solar system is ……………….
(a) Venus
(b) Mercury
(c) Mars
(d) Earth
Answer:
(a) Venus

Question 12.
Which planet is known as Red Planet?
(a) Venus
(b) Saturn
(c) Mars
(d) Neptune
Answer:
(c) Mars

Question 13.
The number of moons present in Saturn is ………………..
(a) 20
(b) 30
(c) 50
(d) 60
Answer:
(d) 60

Question 14.
The planet having the longest summers and winters is ………………….
(a) Saturn
(b) Neptune
(c) Uranus
(d) Jupiter
Answer:
(c) Uranus

Question 15.
Windiest planet in the solar system ………………..
(a) Neptune
(b) Uranus
(c) Saturn
(d) Jupiter
Answer:
a) Neptune

Question 16.
Which among the planets does not have a moon?
(a) Mars
(b) Earth
(c) Uranus
(d) Mercury
Answer :
(d) Mercury

Question 17.
The orbital velocity of the satellite depends on its ……………………
(a) Shape of orbit
(b) altitude
(c) distance
(d) All of these
Answer:
(b) altitude

Question 18.
Which among the following statements is correct?
(i) Meteors are attracted by the gravitational at force of earth.
(ii) Meteors are travelling in low speeds.
(iii) Most of Meteors are burnt by the heat generated by friction in atmosphere.
(a) (i) & (ii)
(b) (ii) & (iii)
(c) (i) & (iii)
(d) All of these
Answer:
(c) (i) & (iii)

Question 19.
The first part of the ISS was launched by
(a) Russian Soyuz
(b) Russian Zarya
(c) Russian Orbital
(d) American Sputnik
Answer:
(b) Russian Zarya

Question 20.
The time is taken by the sun to complete one revolution around the milky way
(a) 250 million years
(b) 200 million years
(c) 225 million years
(d) 240 million years
Answer:
(c) 225 million years

Question 21.
Which of the following statements is correct?
A. There are eight planets in our Solar System.
B. Except Mars, all other planets revolve around the Sun in elliptical orbits.
(a) A only
(b) B only
(c) Both A and
(d) None
Answer:
(a) A only

II. Fill in the blanks :

1. Sun is the star present in the galaxy called ………………
Answer:
milky way

2. The universe began with the start of a massive explosion called ……………..
Answer:
Big Bang

3. Scientists believe that there are ……………… galaxies in the observable universe.
Answer:
one hundred billion (10¹¹)

4. Our closest neighbouring galaxy is ……………
Answer:
Andromeda

5.We can see nearly _______ stars with the naked eye in the dark night
Answer:
3000

6. The brightness of stars depends on their _______ and _____ from the earth.
Answer:
Intensity and distance

7. The Greek name for the Sun is …………………
Answer:
Helios

8. The sun is believed to be more than ______ years ago
Answer:
4.6 billion

9. The inner planets are also known as __________
Answer:
Rocky planets

10. The outer planets are also called as _____
Answer:
Gaseous planets

11. ______ is the brightest heavenly body in our night sky.
Answer :
Venus

12. ______ is called as giant planet
Answer :
Jupiter

13. ________ is the only moon iñ the solar system with clouds.
Answer :
Titan

14. Uranus is a ______ giant
Answer:
cold gas

15. Pluto crosses the orbit of Neptune in every ______
Answer :
248 years

16. The biggest asteroid is …………………
Answer :
Ceres

17. Satellites move around the planets due to ………….. and ……………… force.
Answer :
gravitý, the centripetal

18. The ratio of____ of the periods of any two planets is equal to the ratio of their semi-major axis from the Sun.
Answer :
squares, cubes

19. The temperature of the star is determined by ______
Answer :
Colour

20. ……………… is the only moon in the solar system that moves in the opposite direction to
the direction in which its planet spins.
Answer:
Triton

III. Match the following:

(I)

Answer:
1-c,2-d,3-b,4-a

(II)

Answer:
1-d,2-c,3-a,4-b

(III)

Answer:
1-b,2-a,3-d,4-c,
(IV)

Answer:
1-d,2-c,3-e,4-b,5-g

IV. State whether true or false. If false, correct the statement:

1. The basic constituent of the universe is the luminous matter.
Answer:
True.

2. The important thing about universe is that it is currently shrinking.
Answer:
False.
Correct statement: The important thing about the universe is that it is currently expanding.

3. All the matter in the universe is made up of hydrogen and helium.
Answer:
True.

4. Stars also appear to be in different colours depending on their composition of Gases.
Answer:
False.
Correct statement: Stars also appear to be in different colours depending on their temperature.

5. The planets are revolving around the sun because of the gravitational force of attraction between them.
Answer:
True.

6. The rotation of the sun near the poles takes around 25.4 days.
Answer: False.
Correct statement: The rotation of the Sun near the poles takes around 36 days.

7. Mercury is a special planet from the Sun, almost the same size as Earth.
Answer:
False.
Correct statement: Venus is a special planet from the Sun, almost the same size as Earth.

8. The axis of rotation of the Earth is perpendicular to the plane of its orbit.
Answer:
False.
Correct statement: The axis of rotation of the Earth is not perpendicular to the plane of its orbit.

9. Pole star is not visible from the southern hemisphere.
Answer:
True.

10. Comets revolve around the Sun in highly spiral orbits.
Answer:
False.
Correct statement: Comets revolve around the Sun in highly elliptical orbits.

11. The distance between Saturn and Uranus is about 10 times that between Earth and Mars.
Answer:
False.
Correct statement: The distance between Saturn and Uranus is about 20 times that between Earth and Mars.

V. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both assertion and reason are true and Reason is the correct explanation of Assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion. ,
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion: Earth appears bluish-green.
Reason: This is due to the reflection of light from water and land mass on its surface.
Answer:
(a) If both assertion and reason are true and Reason is the correct explanation of Assertion.

Question 2.
Assertion: Sun is a medium-sized star.
Reason: Sun is situated at the centre of the solar system.
Answer:
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion

Question 3.
Assertion : The outer planets are called as Terrestial Planets.
Reason : Outer planets are made up of hydrogen, helium and other gases in huge amounts and have very dense atmospheres.
Answer:
(d) Assertion is false but reason is true
Assertion : The outer planets are called as Gas giants.

Question 4.
Assertion : The period of revolution of a satellite around a planet is directly proportional to the radius of the orbit of the satellite.
Reason : Artificial satellites do not follow Kepler’s Laws of motion.
Answer:
(c) Assertion is true but reason is false
Reason : Artificial satellites follow Kepler’s laws of motion.

Question 5.
Assertion : At the pole, the value of acceleration due to gravity (g) is greater than equator.
Reason : Earth rotates on its axis in addition to revolving around the sun.
Answer:
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion

VI. Very Short Answer questions :

Question 1.
What is the universe?
Answer:
The collection of all the things that exist in space is known as the universe.

Question 2.
What is a galaxy?
Answer:
A galaxy is a massive collection of gas, dust and billions of stars and their solar systems.

Question 3.
How are galaxies classified?
Answer:
Depending on their appearance, galaxies are classified as

• Spiral,
• Elliptical, (or)
• Irregular.

Question 4.
Why is our galaxy called Milky way?
Answer:
Our galaxy is called milky way galaxy, because it appears as a Milky band of light in the sky.

Question 5.
What is an orbit?
Answer:
A definite curved path in which a planet revolves around the sun is called an orbit.

Question 6.
Define Period of rotation.
Answer:
The time taken by a planet to complete one rotation is called its period of rotation.

Question 7.
Give a reason for changes of seasons on Earth.
Answer:

• Earth is not perpendicular to the plane of its orbit.
• This tilt is responsible for the change of seasons on earth.

Question 8.
Mention the factors responsible for motion of satellite.
Answer:

• Gravity and
• The centripetal force are the factors responsible for motion of satellite

Question 9.
What is a geostationary orbit?
Answer:
A satellite stays in a fixed position relative to a point on Earth’s surface. That is, the satellite stays over the same spot all the time. This kind of orbit is called “Geostationary Orbit”.

Question 10.
How is eye-tracking technology helpful?
Answer:
Eye-tracking technology is helping disabled people with limited movement and speech.

Question 11.
What is a cosmic year?
Answer:
The sun travelling at a speed of 250 km per second (9 lakhs km/h) takes about 225 million years to complete one revolution around the Milky Way. This period is called a cosmic year.

Question 12.
Why are we able to see the Moon even though it is not a luminous body?
Answer:
are able to see the moon, because it reflects the light of the Sun

VII. Answer briefly :

Question 1.
Write notes on the Milky Way.
Answer:

1. Milky Way galaxy is spiral in shape.
2. It is made up of approximately 100 billion stars.
3. Its diameter is 1,00,000 light years.
4. Our solar system is 25,000 light-years away from the centre of our galaxy.

Question 2.
How does a planet differ from a star?
Answer:

Question 3.
Briefly explain (i) brightness (ii) colour of star.
Answer:
Brightness of star:
The brightness of a star depends upon their intensity and distance from the earth. Colour of star:

1. The colour of the stars depends on their temperature.
2. Hot stars are white or blue.
3. Cooler stars are orange or red in colour.

Question 4.
What is a constellation?
Answer:

1. A group of stars forming an imaginary outline or meaningful pattern on the space is called a constellation.
2. They represent an animal, mythological person or creature or an object.
3. 

Question 5.
How is life on earth supported?
Answer:

1. Life on earth is supported by Sun.
2. Solar energy from the Sim has supported and sustained terrestial existence on Earth since the beginning of time.

Question 6.
Write short notes on Asteroids.
Answer:

1. 1. Half a million pieces of rocks that were left over when the planets were formed are called Asteroids.
2. Asteroids revolve around the Sun.
3. Asteroids can only be seen through large telescope.
4. The biggest asteriod is Ceres.

Question 7.
Differentiate Meteors and Meteorites?
Answer:

Question 8.
Write down the formula of orbital velocity.
Answer:
v = \(v=\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+h)}}\)
where v = Orbital velocity.
G = Gravitational constant. (6.673 × 10^-11Nm ²kg^-2
M = Mass of the Earth (5.972 × 10²⁴kg)
R = Radius of Earth (6371 km)
h = Height of thé satellite from the surface of the Earth.

Question 9.
Write short notes on Halley’s comet.
Answer:

1. Halley’s comet is a periodical comet.
2. It appears after nearly everý 76 years.
3. It was last seen in 1986 and will next be seen in 2062

Question 10.
Mention the uses of Robotic arms.
Answer:
Robotic arms

1. Helps in removing inoperable tumours.
2. Takes biopsies with great accuracy.
3. Helpful in breast cancer detection and treatment.
4. Helpful in the development of improved vaccines.

VIII. Answer In detail:

Question 1.
Explain the salient features of the Big Bang Theory.
Answer:
According to the Big Bang Theory,

1. The universe was a hot dense matter.
2. 13.7 billion years ago, an explosion occurred.
3. All the matter is ejected in all directions in the form of galaxies.
4. The galaxies consist of stars which are held together by gravity.
5. The stars explode and planets are liberated throughout the Universe.

Question 2.
How is Sun formed according to Big Bang theory?
Answer:
According to the Big Bang theory.

1. Hydrogen gas condensed to form huge clouds.
2. Some of the hydrogen gas was left free and started floating around. in our galax
3. The free-floating hydrogen gas concentrated and paved way for the formation Sun and solar system.
4. The Sun and solar system turned into a slowly spinning molecular cloud, composed of hydrogen and Helium molecules.
5. The clouds undergo compression due to gravity.
6. The excessive and high-speed spinning of cloud results in flattening into a giant disc.

Question 3.
Give a comparative account of satellites and rings of planets.
Answer:

IX. Numerical problems :

Question 1.
The Earth’s distance from the Sun is 149.6 × 10⁶km and the period of Earth’s revolution is 1 year. Calculate the ratio of the squares of the periods to cubes of the major axis.
Solution :
Semi major axis from sun, R = 149.6 × 10⁶ km.
Period of Earth, T = 1 year.
The ratio = \(\frac{T^{2}}{R^{3}}=\frac{(1)^{2}}{\left(149.6 \times 10^{6}\right)^{3}}\) = 2.98 ×10^-25 year² / km ³.

Question 2.
The mean distance of Earth from the Sun is 149.6 × 10⁶ km and the mean distance of mercury from the sun is 57.9× 10⁶km. The period of Earth’s revolution is 1 year. What is the period of Mercury’s revolution? .
Solution: Given
1. Mean distance of Earth from Sun, r1 = 149.6 × 10 ⁶
2. Mean distance of Mercury from sun, r2 = 57.9 × 10⁶
3. The period of Earth’s revolution, T1 = 1 year
4. The period of Mercury’s revolution, T2 = ?
According to Keplar’s Third Law


Question 3.
Calculate the speed and period of revolution of satellite orbiting at a height 700 km above the Earth’s surface.
Solution:
Given: 1. Height of th Satellite, h = 700 km = 700 x 103 m
We Know: 2. Gravitational constant G = 6.673 × 0^-11 Nm2 kg^-2
3. Mass of the Earth, M = 5.972 × 1024 kg
4. Radius of Earth, R = 6371 km = 6371 × 10³ m
Formula (R + h) = (6371 + 700)km = 7071 km
= 7071 × 10³m=0.7071 × 10⁷m

Period of Revolution T = 5.9 15 × 10³ s
= 5915 sec. (or) 98 min 35 sec.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 11 Atomic Structure Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 11 Atomic Structure

9th Science Guide Atomic Structure Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Among the following the odd pair is

Answer:

Question 2.
Change in the number of neutrons in an atom changes it to
(a) an ion.
(b) an isotope.
(c) an isobar.
(d) another element.
Answer:
(b) an isotope

Question 3.
The term nucleons refer to
(a) protons and electrons
(b) only neutrons
(c) electrons and neutrons
(d) protons and neutrons
Answer::
(d) protons and neutrons

Question 4.
The number of protons, neutrons and electrons present respectively in \({ }_{35}^{80} \mathrm{Br}\) are
(a) 80,80,35
(b) 35,55,80
(c) 35,35,80
(d) 35,45,35
Answer:
(d) 35,45,35

Question 5.
The correct electronic configuration of potassium is
(a) 2,8,9
(b) 2,8,1
(c) 2, 8, 8, 1
(d) 2, 8, 8, 3
Answer:
(c) 2, 8, 8,1

II. State whether true or false. If false, correct the statement:

1. In an atom, electrons revolve around the nucleus in fixed orbits.
Answer:
True.

2. Isotopes of an element have different atomic numbers.
Answer:
False.
Correct statement: Same atomic numbers but different mass numbers.

3. Electrons have negligible mass and charge.
Answer:
True.

4. Smaller the size of the orbit, lower is the energy of the orbit.
Answer:
True.

5. The maximum number of electron in L Shell is 10.
Answer:
False.
Correct statement :The maximum number of electrons in L Shell is 8.

III. Fill in the Blanks :

1. Calcium and Argon are examples of a pair of ………….
Answer:
isobars

2. Total number of electrons that can be accommodated in an orbit is given by …………..
Answer:
the formula 2n²

3. ………….isotope is used in the nuclear reactors.
Answer:
Uranium-235

4. The number of neutrons present in \({ }_{3}^{7} \mathrm{Li}\) is ………….
Answer:
4

5. The valency of Argon is ………………
Answer:
Zero

IV. Match the following :

Answer:
a – 3, b – 5, c – 2, d – 1.

V. Complete the following table :

Answer:

VI. Answer very briefly :

Question 1.
Name an element which has the same number of electrons in its first and second shell.
Answer:
Beryllium. Atomic number – 4 (K-shell-2, L-shell-2)

Question 2.
Write the electronic configuration of K and Cl
Answer:

Question 3.
Write down the names of the particles represented by the following symbols and explain the meaning of superscript and subscript numbers attached. ₁H¹, ₀n¹, _-1C⁰
Answer:
₁H¹ – hydrogen atom mass number 1. Atom number 1.
₀n¹– neutron change 0. Mass 1 amu.
_-1C⁰ – electron change -1. Mass negligible.

Question 4.
For an atom ‘X’, K, L, and M shells are completely filled. How many electrons will be present in it?
Answer:
K – 2, L – 8, M – 18, 28 electrons – Nickel

Question 5.
What is the same about the electron structures of:
a. Lithium, Sodium and Potassium.
b. Beryllium, Magnesium and Calcium.
Answer:
a. Lithium, sodium & potassium have 1 electron in their outermost shell.
b. Beryllium, magnesium and calcium have 2 electrons in their outermost shell.

VII. Answer briefly :

Question 1.
How was it shown that atom has empty space?
Answer:
Rutherford performed an experiment of bombarding a thin gold foil with very small positively charged particles called a particles. He observed that most of the alpha particles passed straight through the foil. He infered by thin experiment that most of the space in the atom is empty.

Question 2.
Why do \({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) have the same chemical properties? In what respect do these atoms differ?
Answer:
\({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) have same chemical properties because they have same number of electrons but their atoms differ in the number of neutrons.

Question 3.
Draw the structure of oxygen and sulphur atoms.
Answer:

Question 4.
Calculate the number of neutrons, protons and electrons :
(i) atomic number 3 and mass number 7
(ii) atomic number 92 and mass number 238.
Answer:
(i) atomic number 3 and mass number 7
∴ No. of electrons (or) No. of protons = 3
Mass number = No. of protons + No. of neutrons
∴ No. of neutrons = 7-3=4

(ii) atomic number 92 and mass number 238
Atomic number = 92
∴ No. of electrons = 92
No. of protons = 92
No. of neutrons = 238-92 = 146

Question 5.
What are nucleons? How many nucleons are present in Phosphorous? Draw its structure.
Answer:

The number of protons and neutrons present in the nucleus are called nucleons. The number of nucleons present is phosphorus is 31.

VIII. Answer in detail :

Question 1.
What conclusions were made from the observations of Gold foil experiment?
Answer:

In Rutherford’s Alpha ray scattering experiment, the following conclusions were made from the observations.

• Atom has a very small nucleus at the centre.
• There is a large empty space around the nucleus.
• The entire mass of an atom is concentrated in a very small positively charged region, which is called Nucleus.
• The electrons are distributed in the vacant space around the nucleus.
• The electrons move in circular paths around the nucleus.

Question 2.
Explain the postulates of Bohr’s atomic model.
Answer:
The main postulates are:

• In atoms, electrons revolve around the nucleus in stationary circular paths called orbits or shells or energy levels.
• While revolving in orbits the electrons do not radiate energy.
• The circular orbits are numbered as 1,2,3,4,… or designated as K, L, M, N, shells. These numbers are referred to as principal quantum numbers (n).
• K shell (n=l) is closest to the nucleus and is associated with lowest energy.
• The energy of each orbit or shell is a fixed quantity and the energy is quantized.

Question 3.
State Gay Lussac’s law of combining volumes, explain with an illustration.
Answer:
Whenever gases react together, the volumes of the reacting gases as well as the products, if they are gases, bear a simple whole number ratio, provided all the volumes are measured under similar conditions of temperature and pressure.
Example:
Step 1: Hydrogen combines with oxygen to form water (word equation) Hydrogen + Oxygen → Water.

i. e. Two volumes of hydrogen reacts with one volume of oxygen to form two volumes of water vapour, i.e. the ratio by volume which gases bears is 2:1:2 which is a simple whole number ratio.
It follows that at a given temperature and pressure, the volumes of all gaseous reactants and products bear a simple whole number ratio to each other.

Intext Activities

ACTIVITY – 1

Symbolically represent the following atoms using the atomic number and mass number, a) Carbon b) Oxygen c) Silicon d) Beryllium
Answer:

ACTIVITY – 2

Assign the valency for Phosphorus, Chlorine, Silicon and Argon
Answer:
Phosphorus – P – 3, 5
Chlorine – Cl – 1
Silicon – Si – 4
Argon – Ar – 0

ACTIVITY – 4

Draw the structures of the isotopes of oxygen O¹⁶ and O¹⁸
Atomic number of oxygen = 8.
Answer:

ACTIVITY – 5

Draw the model of the following pairs of isotones:
(i) Fluorine & Neon (ii) Sodium & Magnesium (iii) Aluminum and Silicon.
Answer:

ACTIVITY – 6

Nitrogen combines with hydrogen to form ammonia (NH3). Illustrate Gay Lussac’s law using this example.
Answer:

1 volume of nitrogen reacts with 3 volumes of hydrogen to form 2 volumes of ammonia gas. The ratio by volume which gases bear is 1 : 3 : 2. Which is a simple while number ratio.

Test Yourself :

Question 1.
Calculate the number of neutrons in the following atoms:

Answer:
Number of neutrons (n) = Mass number (A) – Atomic number (z)
a) \(\frac{27}{13} \mathrm{Al}\) ⇒ Number of neutrons (n) = 27 – 13 = 14
b) \(\frac{31}{15} \mathrm{P}\) ⇒ Number of neutrons (n) = 31-15 = 16
c) \(\frac{190}{76} \mathrm{Os}\) ⇒ Number of neutrons (n) = 190 – 76 = 114
d) \(\frac{54}{24} \mathrm{Cr}\) ⇒ Number of neutrons (n) = 54 – 24 = 30

9th Science Guide Atomic Structure Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Hydrogen atom does not have …………………..
(a) Proton
(b) Neutron
(c) Electron
(d) Proton and electron
Answer:
(b) Neutron

Question 2.
An electron has ……………………
(a) Mass 1/1837^th of proton and positively charged
(b) Mass equal to proton and positively charged.
(c) Mass 1 / 1837^th of proton and negatively charged.
(d) Mass equal to proton and negatively charged.
Answer:
(c) Mass 1/1837^thof proton and negatively charged

Question 3.
Which statement is not correct about isotopes of an element?
(a) Their chemical properties are same.
(b) Their atomic number is same.
(c) Number of electrons are different.
(d) Number of neutrons are different.
Answer:
(c) Number of electrons are different

Question 4.
Co-60 is used in the treatment of …………………..
(a) Cancer
(b) Thyroid disorders
(c) Leukemia
(d) Blockage of arteries.
Answer:
(a) Cancer

Question 5.
Every atom has an equal number of protons and electrons. The nature of the atom is …………………..
(a) Positive
(b) Neutral
(c) Negative
(d) None of the above
Answer:
(b) Neutral

Question 6.
Gold foil alpha particle scattering experiment was performed by …………………..
(a) Dalton
(b) Goldstein
(c) Thomson
(d) Rutherford
Answer:
(d) Rutherford

Question 7.
Which subatomic particles have no charge …………………..
(a) Proton
(b) Neutron
(c) Electron
(d) Proton and electron
Answer:
(b) Neutron

Question 8.
The outermost shell of an atom cannot accommodate electrons more than
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(b)8

Question 9.
The ratio of masses of oxygen in CO and C02 for fixed mass of carbon is 1 : 2. The above is the law of ……………………
(a) Law of multiple proportions
(b) Law of reciprocal proportions
(c) Gay Lussac’s Law of combining volumes
(d) None of the above
Ans:
(a) Law of multiple proportions

Question 10.
………………….. is a radioactive isotope present in our bodv.
(a) Cobalt 60
(b) Uranium 235
(c) Iodine 131
(d) Potassium 40
Answer:
(d) Pottassium 40

Question 11.
Proton was discovered by ………………….
(a) Rutherford
(b) Goldstein
(c) Chadwick
(d) J.J. Thomson
Answer:
(a) Rutherford

Question 12.
Electron was discovered by …………………..
(a) J.J. Thomson
(b) Rutherford
(c) Goldstein
(d) Chadwick
Answer:
(a) J.J. Thomson

Question 13.
α – particles are …………………..
(a) Negative charged particles
(b) Positive charged particles
(c) Beam of Neutrons
(d) gamma radiation
Answer:
(a) Negative charged particles

Question 14.
An α – particle is …………………..
(a) hydrogen Nucleus
(b) a Helium Nucleus
(c) a Proton
(d) an electron
Answer:
(b) a He Nucleus

Question 15.
The electronic configuration of an atom is 2,8,3. The valency of the atom is ……………………
(a) 13
(b) 10
(c) 3
(d) 8
Answer:
(c) 3

Question 16.
The No. of electrons in the outermost shell of the atom of an inert gas ……………………
(a) 0
(b) 1
(c) 2
(d) 8
Answer:
(d) 8

Question 17.
Which one of the following will have the maximum charge / mass ratio?
(a) Electron
(b) Proton
(c) Neutron
(d) a – Particle
Answer:
(a) Electron

Question 18.
The maximum No. of electrons that can be accommodated in M shell is ……………………
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(c) 18

Question 19.
Elements with valency 1 are ……………………
(a) always metals
(b) always metaloids
(c) either metals (or) non-metals
(d) always non – metals
Answer:
(a) always metals

Question 20.
The electronic configuration of ‘Cl’ is ……………………
(a) 2,7
(b) 2,8,8,7
(c) 2,8,7
(d) 2,7,8
Answer:
(c) 2, 8, 7

Question 21.
The isotope used to remove the brain tumour and treatment of Cancer is ……………………
(a) Cobalt 60
(b) Uranium 235
(c) Iodine 131
(d) Na – 24
Answer:
(a) Cobalt 60

II. Fill in the Blanks :

1. ………………….. are the building blocks of matter.
Answer:
Atoms

2. The combination of different elements to form a compound is governed by certain basic rules called …………………..
Answer:
Laws of chemical combination

3. Volume of the nucleus of an atom is ………………….. compared to the volume of the extranuclear part of the atom.
Answer:
very small

4. the Atomic number of an element is 20. It has………………….. valence electrons.
Answer:
2

5. Atoms are so tiny their mass number cannot be expressed in grams but expressed in…………………..
Answer:
atomic mass unit (amu)

6. Elements having completely filled outermost shell, show………………….. valency.
Answer:
Zero

7. A ………………….. number describes a specific aspect of an electron.
Answer:
quantum

8. When an atom gives electrons from its outermost shell, it becomes ………………….. charged.
Answer:
positively

9. The elementary particles such as protons and neutrons are collectively called as…………………..
Answer:
nucleons

10. In two isotopic species number of protons is same but the number of………………….. is different.
Answer:
Neutrons

11. The combination of different elements form a…………………..
Answer:
Compound

12. A compound is governed by basic rules are known as ……………………
Answer:
Laws of chemical combination

13. The ratio of masses of H and O in H₂O is…………….
Answer:
1 : 8

14. α, β, γ rays are during the ratio active decay of an atom.
Answer:
emitted

15. Beryllium + α – rays → Carbon +……………….
Answer:
Neutron

16. …………… = No. of protons = No. of the electrons.
Answer:
Atomic No.

17. ‘A’ is denoted by …………………
Answer:
Mass No

18. ‘Z’ is denoted by . …………………
Answer:
Atomic No

19. Mass No =………………… + No. of Neutrons
Answer:
No. of protons

20. The Mass No. of 27 is for the element…………………….
Answer:
Aluminium

21. U-235 Isotope is used as ………………….
Answer:
Fuel in nuclear reactors

22. The symbol of phosphorus is ……………………….
Answer:
P

23. Na – →……………….. Na⁺.
Answer:
e-

24. Elements with 4 to 7 in their valence shells are …………………
Answer:
non -metals

25. Valency of the elements having ……………..is 1, 2, 3 respectively.
Answer:
Valence electrons 1, 2, 3

26. Atomic orbitals allow atoms to make…………………….. bonds
Answer:
Co-valent

27. The symbol of Azimuthal quantum number is……………………..
Answer:
l

28. The symbol of the Principal quantum number is……………………..
Answer:
n

29. Valency is the combining capacity of ……………………..
Answer:
an atom

III. State whether true or false. If false, correct the statement:

1. In Rutherford’s experiment, bouncing of alpha particles suggests that nucleus of an atom is negatively charged.
Answer:
False
Correct statement: Nucleus of an atom is positively charged.

2. Electrons revolve around the nucleus in definite open shells.
Answer:
False
Correct statement: Electrons revolve around the nucleus in definite closed shells.

3. K and L shell can accommodate a maximum 2 and 8 electrons respectively.
Answer:
True

4. Radio activity of Carbon 14 is considered to determine the age of object, especially of archeological importance.
Answer:
True

5. In a neutral atom number of protons is equal to the number of neutrons.
Answer:
Correct statement: In a neutral atom number of protons is equal to the number of
electrons.

6. If an atom has 6 electrons in its outermost shell, it is inert.
Answer:
Correct statement: If an atom has 8 electrons in its outermost shell, it is inert.

7. The valency of Chlorine is 7.
Answer:
Correct statement: The valency is 1.

8. Smaller the size of the orbit, the smaller the energy of the orbit.
Answer:
True

9. The stability of the nucleus is determined by the Neutron – Proton ratio.
Answer:
True

10. Isotopes of elements have the same chemical properties.
Answer:
True

IV. Match the following :

1.

Answer:
1) – c, 2) – d, 3) – a, 4) – b

2.

Answer:
1) – c, 2) – a, 3) – d, 4) – b

3.

Answer:

a) 4
b) 3
c) 2
d) 1

V. Answer very briefly :

Question 1.
If and element M has mass number 24 and atomic number 12, how many neutrons does its atom contain?
Answer:
Mass number = No. of protons + neutrons
Atomic number = No. of protons
No. of neutrons = 24 – 12 = 12.

Question 2.
Atomic number of A and B are 18 and 19 respectively. What is the electronic configuration of A and B?
Answer:
Electronic configuration of A = 2, 8, 8
Electronic configuration of B = 2, 8, 8, 1.

Question 3.
How will you define the term ‘electronic configuration’?
Answer:
The systematic arrangement of electrons in various shells or orbits in an atom is called the electronic configuration.

Question 4.
Why do the chemical properties of an element are determined by valence electrons?
Answer:
Because they are the one which takes part in the chemical reaction.

Question 5.
What are the elements which have valence electrons 1 or 2 or 3 are called and what are the elements with valence Electrons 4 to 7 in their valence shells?
Answer:
Elements with valence electrons 1 or 2 or 3 are metals and valence electrons with 4 to 7 are non – metals.

Question 6.
How is an atom of the element represented? Give an example.
Answer:
If ‘X’ is the element, atomic mass at the upper left side and atomic number at the lower left side of the symbol of the element.
Example : \({ }_{11}^{23} \mathrm{Na}\) ⇒ 23 →Atomic Mass, 11 →Atomic number.

Question 7.
Why an atom is considered neutral?
Answer:
An atom of an element contains equal number of positively charged protons and negatively charged electrons and so it is neutral.

Question 8.
Name the scientist and his experiment to prove that nucleus of an atom is positively charged.
Answer:
Name of the scientist – Earnest Rutherford
Name of the experiment – Gold foil alpha particle scattering experiment.

Question 9.
Name the particles which determine the mass of an atom?
Answer:
The mass of an atom is determined by protons and neutrons.
Atomic mass = No. of protons + No. of neutrons.

Question 10.
What are the shells?
Answer:
Different energy levels outside the nucleus are called as shells. They are designated as K, L, M, N and numbered as 1, 2, 3…..

Question 11.
Rutherford’s model of an atom has a very small ………….. at the center.
Answer:
Nucleus.

Question 12.
Niels Bohr was Born on …………
Answer:
October 7, 1885.

Question 13.
When an electron returns from high energy level to lower energy level it gives …………
Answer:
It gives off energy.

Question 14.
In \({ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}\)what are the letters A, Z, X stand for?
Answer:
X → symbol of element
Z →Atomic No.
A → Mass No.

VI. Answer briefly :

Question 1.
State the law of reciprocal proportion.
Answer:
If two different elements combine separately with the same weight of a third element, the ratios of the masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine.

Question 2.
Why proton is considered to be the fingerprint of an atom?
Answer:
An atom of an element has its own characteristic number of protons in its nucleus, which distinguishes it from the atoms of other elements. Hence proton is considered to be the fingerprint of an atom.
This characteristic number (Number of protons) is called the atomic number of the element. The atomic number is denoted by Z.

Question 3.
How can an element be identified on the Periodic Table? What makes an element different from another element?
Answer:
An element can be identified by its atomic number which is a representation of the number of protons contained in the nucleus of a particular element. The amount of protons of an element never changes.

Question 4.
Because atoms are so small, what do scientists do?
Answer:
Since atoms are so small, scientists create models to describe them. A model may be a diagram, mental picture, a mathematical statement or an object that helps explain ideas about the natural world.

Question 5.
What are isotopes?
Answer:
Atoms of the same element with the same number of protons and a different number of neutrons – the number of protons will never change! Ex.: Carbon 12, Carbon 13 and Carbon 14 are isotopes of the element carbon.

Question 6.
Draw the diagram of laws of chemical combination.
Answer:
Laws of chemical combination

Question 7.
Define Isobars.
Answer:
Isobars are the atoms of the different elements of same mass number but different atomic number.

Question 8.
What is a combination reaction?
Answer:
A combination reaction is a reaction where two or more substances combine to form a single substance.
The combination of different elements to form a compound is governed by certain basic rules. These rules are known as Laws of chemical combination.

Question 9.
What are the salient features of Rutherford’s model of an atom?
Answer:
RUTHERFORD’S MODEL OF AN ATOM- Salient features

• Atom has a very small nucleus at the center.
• There is large empty space around the nucleus.
• Entire mass of an atom is concentrated in a very small positively charged region which is called the nucleus.
• Electrons are distributed in the vacant space around the nucleus.
• The electrons move in circular paths around the nucleus.

Question 10.
What are the Limitations of Bohr’s Model?
Answer:
Limitations of Bohr’s model:

• One main limitation was that his model was applicable only to Hydrogen.
• It could not be extended to multi-electron atoms.
• Hence more research and deeper study of atoms became necessary.

Question 11.
Explain the Composition of the Nucleus.
Answer:
COMPOSITION OF NUCLEUS

• Electrons have a negligible mass; hence the mass of the atom mainly depends on the mass of the nucleus. Nucleus of an atom consists of two components, they are protons and neutrons.
• Protons are positively charged. Protons repel each other because of their like charges. Hence more than one proton cannot be packed in a small volume to form a stable nucleus, unless neutrons are present.
• Neutrons reduce the repulsive force between the positively charged protons and contribute to the force that holds the particles in the nucleus together.

Question 12.
Define the Nucleons.
Answer:
Nucleons: The elementary particles such as protons and neutrons are collectively called as Nucleons.

Question 13.
What are the relation between mass no. & atomic no?
Answer:
Relationship between Mass Number and Atomic Number:
Mass Number (A) = Number of Protons + Number of Neutrons(n)
Atomic Number (Z) = Number of Protons or Number of Electrons
Mass Number = Atomic Number (Z) + Number of neutrons (n)
A = Z + n.

Question 14.
What are the types of Quantum Number?
Answer:

Question 15.
Draw the atomic structure of Mg (At. No. 12, Mass No. 24)
Answer:

Question 16.
Compare the charge and mass of protons and electrons.
Answer:

Question 17.
Ca²⁺ has completely filled outer shell. Justify your answer.
Answer:
The atomic number of Calcium is 20. It has K = 2, L = 8, M = 8, N = 2.
If we remove the last 2 electrons, that is from N shell, Ca2+ and we will be having 8 in the outermost shell (M shell). So we have completely filled outer shell. (The maximum 8 electrons in a shell is a completely filled shell).

Question 18.
State the law of multiple proportion. .
Answer:
When two elements A and B combine together to form more than one compound, then masses of A which separately combines with a fixed mass of B are in simple ratio.

Question 19.
List the uses of isotopes.
Answer:
Uranium 235 – Used as fuel in nuclear reactors
Cobalt 60 – Used in the treatment of cancer
Iodine 131 – Used in the treatment of goitre.
Carbon 14 – To find the age of plants and animals.

Question 20.
What is isotone? Give an example.
Answer:
Atoms of different elements with different atomic numbers and different mass numbers, but with the same number of neutrons are called isotones.
Example: Pair of elements Boron and Carbon has the same number of neutrons but
different number of protons and hence different atomic numbers.

VII. Answer in detail :

Question 1.
Prove that in the following example, Sulphur and Oxygen combine using the law of reciprocal proportions.
Answer:
Oxygen and sulfur react with copper to give copper oxide and copper sulfide, respectively. Sulphur and oxygen also react with each other to form S02. Therefore,

in CuS ⇒ Cu : S = 63.5 : 32
in CuO ⇒ Cu : O = 63.5 : 16
S : 0 = 32 : 16 ⇒ S:0= 2:1
Now in SO₂:
S : 0 = 32 : 32 ⇒ S: 0 = 1:1
Thus the ratio between the two ratios is 2 : 1
This is a simple multiple ratio.

Question 2.
Explain about radioactive decay and radioactive isotopes.
Answer:
When the nucleus of an atom possesses either too many or too few neutrons compared to the number of protons it becomes unstable. These are called radioactive isotopes. Unstable nuclei split up in a process called radioactive decay and emit radioactive radiation.

Many elements have isotopes of which some of them are radioactive isotopes. There is a lot of low-level natural radioactivity around us. For example, our bodies contain radioisotopes, such as Potassium – 40, which continuously emit radiation, but because the amount is very low this does not harm us. Carbon -14 is a radioactive isotope used to date organic material.

Question 3.
Describe the limitations in Rutherford’s model.
Answer:

• According to electromagnetic theory, a moving electron, accelerate and continuously lose energy.
• Due to the loss of energy, path of the electron may reduce and finally the electron fall into the nucleus.
• If it happens so, atom becomes unstable. But atom are stable. Thus Rutherford’s model failed to explain the stability of an atom.

Question 4.
Explain the electronic configuration of atoms with an illustration.
Ans. Electronic configuration of atoms:

• Electrons occupy different energy levels called orbits or shells.
• The distribution of electrons in these orbits of an atom is governed by certain rules or conditions. These are known as Bohr and Bury Rules of electronic configuration.
• Bohr and Bury simultaneously proposed the following rules for the distribution of electrons in different shells.

Rule 1: The maximum number of electrons that can be accommodated in a shell is equal to 2n² where ‘n’ is the quantum number of the shell (i.e., the serial number of the shell from the nucleus).
Shell Value of (n) Maximum number of electrons (2n2)

Rule 2: Shells are filled in a stepwise manner in the increasing order of energy.
Rule 3: The outermost shell of an atom cannot have more than 8 electrons even if it has the capacity to accommodate more electrons. For example Electronic configuration in Ca

Illustration:

Question 5.
Explain the valence electron and valency with an illustration.
Answer:

Valence elect runs
How many electrons are in the outermost shell of nitrogen? 5 The outermost shell of an atorh is called its valence shell and the electrons present in the valence shell are known as valence electrons.

The chemical properties of elements are decided by these valance electrons, since they are the ones that take part in chemical reaction.

The elements with same number of electrons in the valence shell show similar properties and those with a different number of valence electrons show different chemical properties. Elements, which have valence electrons 1 ‘ or 2 or 3 (except Hydrogen) are metals.

These elements can lose electrons to form ions which are positive charged and are called cations.

Elements with 4 to 7 electrons in their valence shells are non-metals.
These elements can gain electrons to form ions which are negatively charged and are called anions

VALENCY:

Valency of the element is the combining capacity of the element with other elements and is equal to the number of electrons that take part in a chemical reaction. The valency of the elements having valence electrons 1, 2, 3 is 1, 2, 3 respectively.
While valency of element with 4, 5, 6 & 7 valence electron is 4, 3, 2 and 1 (8 – valence electrons) respectively. Elements having completely filled the outermost shell show Zero valency.

For example The electronic configuration of Neon is 2,8 (completely filled). So valency is 0

Illustration:
Assign the valency of Magnesium & Sulphur.
Electronic configuration of magnesium is 2, 8, 2. So valency is 2.
The electronic configuration of sulphur is 2, 8, 6. So valency is 2 i.e. (8 – 6).

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 10 Matter Around Us Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 10 Matter Around Us

9th Science Guide Matter Around Us Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
The separation of denser particles from lighter particles done by rotation at high speed is called ………………
(a) Filtration
(b) sedimentation
(c) decantation
(d) centrifugation
Answer:
(d) centrifugaton

Question 2.
Among the following ……………… is a mixture.
(a) Common Salt
(b) Juice
(c) Carbon dioxide
(d) Pure Silver
Answer:
(b) Juice

Question 3.
When we mix a drop of ink in water we get a . ………………
(a) Heterogeneous Mixture
(b) Compound
(c) Homogeneous Mixture
(d) Suspension
Answer:
(c) Homogeneous Mixture

Question 4.
……………….is essential to perform separation by solvent extraction method.
(a) Separating funnel
(b) filter paper
(c) centrifuge machine
(d) sieve
Answer:
(a) Separating funnel

Question 5.
………………… has the same properties throughout the sample.
(a) Pure substance
(b) Mixture
(c) Colloid
(d) Suspension
Answer:
(a) Pure substance

II. State whether true or false. If false, correct the statement.

1. Oil and water are immiscible in each other.
Answer:
True.

2. A compound cannot be broken into simpler substances chemically.
Answer:
False
Correct statement: A compound can be broken into simpler substances chemically.

3. Liquid – liquid colloids are called gels
Answer:
False.
Correct statement: Liquid – solid colloids are called gels.

4. Buttermilk is an example of heterogeneous mixture.
Answer:
True.

5. Aspirin is composed of 60% Carbon, 4.5% Hydrogen and 35.5% Oxygen by mass. Aspirin is a mixture.
Answer:
False.
Correct statement: It is Compound. It is because the components are combined in a fixed ratio by mass.

III. Match the following :

Answer:

IV. Fill in the blanks :

1. A …………………. mixture has no distinguishable boundary between its components.
Answer:
Homogeneous

2. An example of a substance that sublimes is…………
Answer:
Dry ice / Solid CO₂ / Camphor

3. Alcohol can be separated from water by ………….
Answer:
Fractional distillation

4. In petroleum refining, the method of separation used is ………….
Answer:
Fractional distillation

5. Chromatography is based on the principle of………….
Answer:
different solubilities

V. Very Short answer :

Question 1.
Differentiate between absorption and adsorption.
Answer:
Absorption

1. Absorption is the process in which the substance is dissolved throughout the bulk of another substance.
2. For example a paper (absorbent) soaks up or absorbs water.

Adsorption

1. Adsorption is the process in which particles of a substance, (it could be gas, liquid or dissolved solid) adhere to a surface of another substance.
2. For example: charcoal adsorbs gases on its surface. Charcoal is called the adsorbent and the gas is called the adsorbate.

Question 2.
Define Sublimation.
Answer:
Certain solids change directly to a gas without passing through the liquid is called sublimation.

Question 3.
A few drops of ‘DettoP when added to water the mixture turns turbid. Why?
Answer:
The Dettol formulation is a stabilised micro-emulsion. It is manufactured using Chloroxylenol 4.8% and the rest made up by pine oil, isopropanol, castor oil, and soap. On dilution with water, the micro-emulsion destabilises releasing the pine oil and castor oil as a visible bloom. That is why the mixture turns turbid.

Question 4.
Name the apparatus that you will use to separate the components of mixtures containing two, i. miscible liquids, ii. immiscible liquids.
Answer:

1. Miscible liquids – Fractional distillation (Fractionating column and Liebig) Condenser
2. Immiscible liquids – Separating funnel

Question 5.
Name the components in each of the following mixtures.

1. Ice cream
2. Lemonade
3. Air
4. Soil

Answer:

1. Ice cream is a mixture of cream, milk, sugar & sometimes egg.
2. Lemonade is a mixture of lemon juice, sugar and water.
3. Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour, and other gases.
4. Soil is a mixture of clay, sand and various salts.

VI. Answer briefly

Question 1.
Which of the following are pure substances?
Ice, Milk, Iron, Hydrochloric acid, Mercury, Brick, and Water.
Answer:
Ice, Iron, Hydrochloric acid, Mercury, and water are pure substances.

Question 2.
Oxygen is very essential for us to live. It forms 21 % of air by volume. Is it an element or a compound?
Answer:
Oxygen is an element.

Question 3.
You have just won a medal made of 22-carat gold. Have you just procured a pure substance or impure substance?
Answer:
I have procured an impure substance. It is made of 22 parts of pure gold and 2 parts of copper or silver.

Question 4.
How will you separate a mixture containing sawdust, naphthalene and iron filings?
Answer:
The iron filings in the mixture can be separated by Magnetic separation and Naphthalene by sublimation. Sawdust will be remaining at the bottom.

Question 5.
How are homogenous solutions different from a heterogeneous solutions? Explain with examples.
Answer:
Homogeneous mixtures

1. Components are uniformly mixed and it will have a single phase,
   Eg: Alloys, salt solution, lemonade, petrol etc.
2. No boundaries of separation between the components. Has a single phase.
3. Components are not visible to the naked eye.
4. They will be in solid, liquid or in the gaseous phase.

Heterogeneous mixtures

1. Components are not uniformly mixed and it will have more than a single phase. They are called suspensions. Eg: chalk in water, petrol in water, sand in water, etc.
2. There are visible boundaries between the components. Have two or more distinct phases.
3. Components are visible to the naked eye.
4. Can be a solid-liquid or solid-gas or liquid-gas or solid-solid, or liquid-liquid mixtures.

VII. Answer in detail:

Question 1.
Write the differences between elements and compounds and give an example for each.
Elements

1. Contains only one kind of atoms.
2. It is a pure substance.
3. Cannot be broken down further into to simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Copper (Cu), Silicon (Si), Gold (Ag)

Compounds

1. Contains more than one kind of atoms.
2. It is not a pure substance.
3. Can be broken down further into simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Water (H₂0), Carbon dioxide (CO₂), Ammonia (NH₃)

Question 2.
Explain the Tyndall effect and Brownian movement with a suitable diagram.
Answer:
Brownian Movement:
Brownian movement is a kinetic property. When colloidal solutions are viewed under a powerful microscope,it can be seen that colloidal particles are moving constantly and rapidly in zig-zag directions.

The Brownian movement of particles is due to the unbalanced bombardment of the particles by the molecules of the dispersion medium.

Tyndall effect:

• Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution, the path of the beam becomes visible.
• This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone.
• This phenomenon is not observed in case of true solution.
  
• This phenomenon is due to scattering of light by colloidal particles.

Question 3.
How is a mixture of common salt, oil, and water separated? You can use a combination
of different methods.
Answer:

• The mixture is taken in a separating funnel., whose mouth is kept closed.
• Oil and water are immiscible liquids.
• As common salt can dissolve in water it settles as a separate layer at the bottom of the oil layer in the separating funnel.
• Place a beaker below the funnel to collect salt solution.
• Open the tap. Allow the salt solution alone to collect in the beaker.
• From the salt solution, common salt is obtained from evaporation.

Intext Activities

ACTIVITY – 1

1. Is air a pure substance or Mixture? Justify
2. You must have seen brass statues in museums and places of worship. Brass is an alloy made up of approx. 30% zinc and 70% copper. Is Brass a pure substance or a mixture or compound?
Answer:
1. Air is a mixture.
Reason: Air contains nitrogen, oxygen, carbon dioxide, dust particles, water vapour. The composition of air is not the same at all places.
2. Brass is a mixture of solid in solid.

ACTIVITY – 3

Take some powdered iron filings and mix them with sulphur.
i. Divide the mixture into two equal halves.
ii. Keep the first half of the mixture as it is, but heat the second half of the mixture.
iii. On heating you will get a black brittle compound.

Solution:

• When Iron fillings and sulphur are mixed both retain their properties it means they have not undergone any chemical reaction.
  Iron + Sulphur → dirty yellow powder
• When Iron fillings and sulphur are mixed and heated, they undergo a chemical reaction and form Iron sulphide
  
• The black brittle compound is iron sulphate.

ACTIVITY – 4

Identify whether the given substance is a mixture or compound and justify your answer.
1. Sand and water, 2.Sand and iron filings, 3.Concrete, 4. Water and oil, 5. Salad, 6. Water 7. Carbon dioxide, 8. Cement, 9. Alcohol.
Solution :

ACTIVITY – 5

1. Take bottles containing sugar, starch, and wheat flour.
2. Add one teaspoon full of each one to a glass of water and stir well. Leave it aside for about ten minutes.
What do you observe?
Answer:

When one teaspoon full of sugar, starch and wheat flour are added to a glass of water, sugar dissolves in water but wheat flour does not. If we leave it aside for about 10 minutes, wheat flour settles at the bottom

Test Yourself :

Question 1.
Why whole milk is white?
Answer:
Milk is white because it reflects all wavelengths of visible light. The mixture of reflected colors produces white light. The reason for this is due to the chemical composition of milk and the size of the particles contained within it.

Question 2.
Why the ocean is blue?
Answer:
The ocean looks blue because red, orange, and yellow (long-wavelength light) are absorbed more strongly by water than is blue (short-wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue.

Question 3.
Why the sun looks yellow when it is really not?
Answer:
Our sun is actually white (a mixture of all wavelength of visible spectrum) if we see it from outer space or high-altitude airplanes. Our atmosphere scatters shorter to bigger wavelengths color from sunlight when the white light travels through it. During day, it scatters violet and blue colours leaving yellowish sunlight (the reason why sky is blue and sunlight is yellow). During morning and evening, the sun appears reddish because light rays needs to travel longer distance in atmosphere which causes scattering of yellow light too.

9th Science Guide Matter Around Us Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Liquids have
(a) definite volume, definite shape and are not compressible.
(b) definite volume, no definite shape and are highly compressible.
(c) no definite volume, no definite shape, and slightly compressible
Answer:
(b) definite volume, no definite shape, and slightly compressible

Question 2.
Intermolecular space is maximum in
(a) solids
(b) liquids
(c) gases
(d) all the above
Answer:
(c) gases

Question 3.
Air is a/an,
(a) compound
(b) element
(c) Mixture
(d) Molecule
Answer:
(c) Mixture

Question 4.
Which statement is not correct for a mixture
(a) Components retain their properties
(b) Properties of a mixture are different from its components
(c) Components are mixed in any ratio
(d) Components are separated using simple methods
Answer:
(b) Properties of a mixture are different from its components

Question 5.
A homogeneous mixture of two or more substances is called
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) None of the above.
Answer:
(a) True solution

Question 6.
A colloidal solution is a
(a) Homogeneous mixture
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes
(c) Heterogeneous mixture in which dissolved particles can be seen with naked eyes
(d) All the above
Answer:
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes

Question 7.
Muddy water is an example of
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(b) Suspension

Question 8.
The solution of soap in water is
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(c) Colloidal solution

Question 9.
Water is a/an
(a) element
(b) Mixture
(c) Molecule
(d) compound
Answer:
(d) compound

Question 10.
When two or more elements combine together they form
(a) element
(b) compound
(c) Mixture
(d) Molecule
Answer:
(b) compound

Question 11.
Which of the following will show the “Tyndall Effect”?
(a) Salt solution
(b) Milk & starch solution
(c) Copper sulphate solution
(d) Sugar solution
Answer:
(b) Milk & starch solution

Question 12.
Solid is an arrangement of particles
(a) close together
(b) far together
(c) far apart
(d) none of these
Answer:
(a) close together

Question 13.
The movement of particles in liquids is …………………..
(a) Vibrate on the spot
(b) around each other
(c) Move quicks in all direction
(d) none of these
Answer:
(b) around each other

Question 14.
Gases change to liquid by the process of . …………………..
(a) Melting
(b) Vapourising
(c) Condensing
(d) Freezing
Answer:
(c) Condensing

Question 15.
The physical state of water at 373 K is …………………..
(a) solid
(b) liquid
(c) vapour
(d) plasma
Answer:
(c) vapour

Question 16.
The constituents that form a mixture are also called …………………..
(a) Elements
(b) Compounds
(c) Alloys
(d) Components
Answer:
(d) Components

II. True or False? If false, correct the statement:

1. Atoms are the tiny particles which repel each other when they are squeezed very close.
Answer:
True

2. A teabag placed in a cup of hot water will diffuse into the water.
Answer:
True

3. Evaporation does form bubbles.
Answer:
False
Correct statement: No does not, only boiling forms bubbles.

4. The energy for the process of sublimation can be derived either from the surroundings or from the heat supplied.
Answer:
True

5. The pressure of gases does not depend on the temperature of the gas and the volume it occupies
Answer:
False
Correct statement: The pressure of gases does depend on the temperature of the gas and the volume it occupies

6. Higher the temperature, higher the kinetic energy of particles.
Answer:
True

7. Solids do not flow.
Answer:
True

8. Gases do not diffuse very easily.
Answer:
False.
Correct statement: Gases diffuse very easily.

9. Mixtures are impure substances.
Answer:
True.

10. Salt solution is an example of a heterogeneous mixture.
Answer:
False.
Correct statement: The salt solution is an example of a homogeneous mixture.

III. Match the following :

1. (i)

Answer:
1) – c, 2) – d, 3) – e, 4) – a, 5) – b

(ii)

Answer:
1) – c, 2) – e, 3) – b, 4) – a, 5) – d

2. Match the following.

Answer:
1 – d, 2 – a, 3 – b, 4 – c.

3. Match the following.

Answer:
1 – c, 2 – a, 3 – d, 4 – b.

IV. Fill in the blanks :

1. A substance must absorb …………….. so that it can melt.
Answer:
heat energy

2. Boiling refers to the process by which a substance changes from the liquid to the gaseous state at its …………. point.
Answer:
boiling

3. ………………… is used for industrial refrigeration and transporting frozen food.
Answer:
Dry ice

4. ……………….. is the SI unit of temperature
Answer:
Kelvin

5. Elements contain the …………………of the same kind
Answer:
atoms

6. When elements are physically mixed they form…………………
Answer:
mixtures

7. A compound has a definite …………………
Answer:
formula

8. Mixture of iron filings and salt is a …………………type of mixtures.
Answer:
heterogeneous

9. …………………is the major difference between true solutions, suspensions and colloids.
Answer:
Particle size

10. Phenomenon of Evaporation takes place at the …………………of a liquid.
Answer:
Surface

11. Inverse of sublimation is called …………………
Answer:
deposition

12. Expand LPG …………………
Answer:
Liquefied Petroleum Gas

13. LPG is ………………… gas.
Answer:
inflammable hydrocarbon

14. Compressibility of solids: …………………..
Answer:
can’t be compressed

15. Fluidity of solids: …………….
Answer:
do not flow

16. A mixture does not have fixed …………………….
Answer:
boiling point (or) melting point

17. A compound has a fixed ………………….
Answer:
boiling point (or) melting point

18. The mixture of Iron filling and sale is …………………
Answer:
heterogeneous

19. Gas-solid is ……………………
Answer:
Solid foam

20. Examples of foam is ……………
Answer:
Soap lather / Aerated water

21. Evaporation is always accompanied by…………..in temperature.
Answer:
decrease / cooling effect

V. Very short answer:

Question 1.
Define ‘matter’.
Answer:
The matter is anything that has mass & occupies space.

Question 2.
What are the three states of matter?
Answer:
Solids, liquids, and gases are the three states of matter.

Question 3.
What is an atom?
Answer:
The smallest unit of an element which may or may not have an independent existence but always take part in a chemical reaction is called an atom.

Question 4.
What is a molecule?
Answer:
The smallest unit of a pure substance which always exist independently and can retain physical and chemical properties of that substance is called a molecule.

Question 5.
Give an example for a molecule.
Answer:
Hydrogen molecule – consists of 2 atoms of hydrogens.

Question 6.
How is matter classified?
Answer:
Matter is classified as pure and impure substances.

Question 7.
How are pure substances classified?
Answer:
Pure substances are classified as elements and compounds.

Question 8.
Give examples of pure substances.
Answer:
Copper, oxygen, hydrogen.

Question 9.
How are impure substances classified?
Answer:
Impure substances are classified as homogeneous and heterogeneous.

Question 10.
How are elements classified?
Answer:
Elements are classified as metals, non-metals, and metalloids.

Question 11.
Give examples for metalloids.
Answer:
Boron, silicon, germanium, and arsenic.

Question 12.
Give the chemical formula for cane sugar.
Answer:
C₁₂H₂₂O₁₁

Question 13.
Expand LPG.
Answer:
Liquefied petroleum gas.

Question 14.
Name the element which is used in toothpaste to strengthen our teeth.
Answer:
Fluorine.

Question 15.
Name the compounds used in fertilizers.
Answer:
Compounds of phosphorus, nitrogen, and potassium are used in fertilizers.

Question 16.
Is blood a pure substance?
Answer:
No blood is not a pure substance. It is a mixture of components such as platelets, red and white blood corpuscles, and plasma.

Question 17.
Name the two types of mixtures.
Answer:
Homogeneous and heterogeneous.

Question 18.
Name some substances that sublime.
Answer:
Camphor, Naphthalene, Mothballs.

Question 19.
Name a suitable method used to separate two immiscible liquids.
Answer:
Separating funnel.

Question 20.
Name a method used to separate two miscible liquids.
Answer:
Fractional distillation.

Question 21.
Name the machine used in the centrifugation process.
Answer:
Centrifuge.

Question 22.
Give an example for liquid in gas.
Answer:
Aerosol.

Question 23.
What is “Brownian motion”?
Answer:
The erratic random movement of microscopic particles in a fluid, as a result of ‘ continuous bombardment from molecules of the surrounding medium was discovered by the scientist Robert Brown and so the movement is called “Brownian motion”

VI. Short answer :

Question 1.
What is an element? ’
Answer:
Each element is made up of only one kind of atom. Element is the building block of all materials. The element of any substance cannot be broken down further into simple substances.

Question 2.
What is a compound?
Answer:
When 2 or more elements combine chemically to form a new substance, the new ‘ substance is called a compound.
Example: H₂O.

Question 3.
What is a mixture?
Answer:
A mixture is an impure substance which contains 2 or more kinds of elements or ‘ compounds or both physically mixed together in any ratio.

Question 4.
What is LPG?
Answer:
LPG is liquefied petroleum gas. It contains a mixture of butane and propane gas.

Question 5.
Distinguish an element and a compound.
Answer:
Element:

1. Made up of only one kind of atom.
2. The smallest particle that retains all its properties in the atom cannot be broken down into simpler substances.

Compound:

1. Made up of more than one kind of atom.
2. The smallest particle that retains all the properties in the molecule can be broken down into elements by chemical methods.

Question 6.
Define sublimation.
Answer:
Certain solid substances when heated change directly from solid to gaseous state without attaining liquid state. The vapours when cooled give back the solid substance. This process is known as sublimation.

Question 7.
What is centrifugation?
Answer:
Centrifugation is the process by which fine insoluble solids from a solid liquid mixture can be separated in a machine called a centrifuge.

Question 8.
What is solvent extraction?
Answer:
Solvent extraction method is used to separate two immiscible liquids. This method works on the principle of difference in solubility of two immiscible liquids in a suitable solvent.

Question 9.
What is distillation?
Answer:
Distillation is the process of obtaining pure liquid from a solution. It is actually a combination of evaporation and condensation.

Question 10.
What is fractional distillation?
Answer:
Fractional distillation is used to separate two or more miscible liquids that do not differ much in their boiling points, (less than 25K).

Question 11.
What is chromatography?
Answer:
Chromatography is a separation technique. It is used to separate different components of a mixture based on their different solubilities in the same solvent.

Question 12.
What is paper chromatography?
Answer:
Paper chromatography is used .to separate the different coloured dyes in a sample. It is based on the principle of different solubility in the solvent which is absorbed to different extents by the chromatography paper.

Question 13.
What is a solution?
Answer:
A solution is a homogeneous mixture of two or more substances.

Question 14.
What is a solute?
Answer:
In a solution, the component present in a lesser amount by weight is solute.

Question 15.
What is the solvent?
Answer:
In a solution, the component present in a larger amount by weight is solvent.

Question 16.
What are Colloidal Solutions?
Answer:
A colloidal solution is a heterogeneous system consisting of the dispersed phase and the
dispersion medium.

Dispersed phase

1. Component present in smaller proportion
2. Analogous to solute of a true solution

Dispersion medium

1. Component present in larger proportion
2. Analogous to solvent of a true solution

Question 17.
What is Tyndall effect?
Answer:
Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution the path of the beam becomes visible. This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone. This phenomenon is not observed in case of true solution.

Question 18.
What are the Types of emulsions?
Answer:
The two liquids mixed can form different types of emulsions. For example, oil and water can form an oil in water emulsion, where the oil droplets are dispersed in water, or they can form a water in oil emulsion, with water dispersed in oil.

Question 19.
What are the uses of emulsions?
Answer:
Emulsions find wide applications in food processing, pharmaceuticals, metallurgy, and many other important industries.

VII. Answer in detail :

Question 1.
What are the characteristics of Pure Substances? (or) List out the characteristics of Pure Substances.
Answer:

• Made up of only one kind of atom or molecule.
• The ratio of the components of a pure substance is fixed.
• Have a characteristic set of properties. Physical properties like boiling point, melting point, density etc. are
• fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Has the same composition throughout i.e it is homogenous in nature

Question 2.
List out the characteristics of Mixtures.
Answer:

• The constituents of a mixture are loosely held together without any chemical force between the constituents and in such a case the constituents retain their individual properties.
• A mixture can be prepared by mixing the constituents in any proportion i.e mixtures do not have any fixed amount of constituents Formation of mixtures does not involve any exchange of energy.
• Mixtures do not have any characteristic set of properties. Physical properties of mixtures like boiling point, melting point, etc. are not fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Components of a mixture can be separated by physical methods.

Question 3.
Tabulate Differences between mixtures and compounds.
Answer:
Mixtures

1. A mixture can be separated into its constituents by physical processes like filtration, evaporation, sublimation, magnet distillation, solvent extraction.
2. A mixture retains or shows the properties of its constituents
3. Energy (in the form of heat light etc.) is neither given out nor absorbed in the preparation of a mixture
4. The composition or proportion is variable a mixture does not have a definite formula
5. A mixture does not have a fixed boiling point or melting point

Compounds :

1. A compound cannot be separated into its constituents by physical processes but can be only separated by a chemical process
2. The properties of a compound are entirely different from those of its constituent elements
3. Energy (in the forth of heat, light etc.) is given out or absorbed during the preparation of a compound
4. The composition of a compound is fixed. The constituents are present in a fixed ratio by mass. The compound has a definite formula.
5. A compound has a fixed boiling point or melting point

Question 4.
Write the Classification of colloids based on physical state of dispersed phase and dispersion medium.
Answer:
Dispersed phase or the dispersion medium can be a solid, or liquid or gas. There are eight different combinations possible (The combination in which both the dispersed phase and dispersion medium are gases does not exist as gases are completely miscible and can never give rise to a colloidal solution).

Question 5.
Two immiscible liquids are taken in the above funnel for separation.
Which is denser, X or Y? Suggest any one example for X and one for Y. A third liquid Z which is soluble only in Y is added to the mixture and contents in the funnel are shaken well. How many layers will you observe now? How will you separate the three liquids? Boiling point of X is 98°C, that of Y is 43°C and that of Z is 75°C.
Answer:
Boiling point of the 3 liquids are given as
X is 98°C – Which corresponds to water.
Y is 43°C – Which corresponds to oil.
Z is 75°C – Which corresponds to alcohol.
‘Y’ is more denser.
Only two layers are observed. X is separated by separating funnel, Z is separated by distillation method. Y – is in the distillation flask.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 8 Sound Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 8 Sound

9th Science Guide Sound Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following vibrates when a musical note is produced by the cymbals in a orchestra?
(a) stretched strings
(b) stretched membranes
(c) air columns
(d) metal plates
Answer:
(d) metal plates

Question 2.
Sound travels in air:
(a) if there is no moisture in the atmosphere.
(b) if particles of medium travel from one place to another.
(c) if both particles as well as disturbance move from one place to another.
(d) if disturbance moves.
Answer:
(d) if disturbance moves

Question 3.
A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through
(a) wax
(b) vacuum
(c) water
(d) empty vessel
Answer:
(b) vacuum

Question 4.
The maximum speed of vibrations which produces audible sound will be in
(a) seawater
(b) ground glass
(c) dry air
(d) Human blood
Answer:
(b) ground glass

Question 5.
The sound waves travel faster
(a) in liquids
(b) in gases
(c) in solids
(d) in vacuum
Answer:
(c) in solids

II. Fill in the blanks.

1. Sound is a ……………….wave and needs a material medium to travel.
Answer:
longitudinal mechanical

2. Number of vibrations produced in one second is………………..
Answer:
Frequency

3. The velocity of sound in solid is …………… than the velocity of sound in air.
Answer:
greater

4. Vibration of object produces ……………..
Answer:
Sound

5. Loudness is proportional to the square of the ……………………
Answer:
Amplitude of vibration of sound

6. …………..is a medical instrument used for listening to sounds produced in the body.
Answer:
Stethoscope

7. The repeated reflection that results in persistence of sound is called ……………………
Answer:
Reverberation

III. Match the following :

Answer:
1 – e, 2 – d, 3 – a, 4 – b, 5 – c

IV. Answer in brief :

Question 1.
Through which medium sound travels faster, iron or water? Give reason.
Answer:
Sound travels faster through iron than water.
Reason: The speed of sound depends on the nature of the medium. As Iron is a solid, sound travels faster through iron than Water.

Question 2.
Name the physical quantity whose SI unit is ‘hertz’. Define.
Answer:
The SI unit of frequency is Hertz. Frequency is the number of waves produced in one second.

Question 3.
What is meant by supersonic speed?
Answer:
Supersonic speed is the speed of an object that exceeds the speed of sound in air (330 ms^-1).

Question 4.
How does the sound produced by a vibrating object in a medium reach your ears?
Answer:

• When an object vibrates, it sets the particles of the medium around it vibrating.
• The vibrating particles in the medium displace from the equilibrium position and exerts pressure on adjacent particles.
• Thus this process continues in the medium till the sound reaches our ear.

Question 5.
You and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
We cannot hear any sound on the moon.
Reason: Absence of atmosphere (medium) in the moon.

V. Answer in detail :

Question 1.
Describe with a diagram, how compressions and rarefactions are produced.
Answer:
Compressions :
When a vibrating body moves forward, it creates a region of high pressure is known as compressions. In compression, the particles are denser. Compressions are the region where particles are crowded together.

Rarefaction :
When the vibrating body moves backward, it creates a region of low pressure (i.e) low density of particles. This is called rarefaction. Rarefactions are the regions where particles are spread apart.

Question 2.
Verify experimentally the reflection of the laws of sound.
Answer:

• Make two identical long pipes using chart paper.
• Arrange them on a table near wall.
• Keep a clock near the open end of one pipe and hear the sound of the clock through the other pipe.
• Adjust the pipe till the sound of the clock heard with more clarity.
• Now measure the angle of incidence and reflection and see the relationship between the angles.
• The angle in which the sound is incident is equal to the angle in which sound is reflected.
• Direction of incident sound, direction of the reflected and the normal are in the same plane.
• Thus laws of reflection of sound are verified.

Question 3.
List the applications of sound.
Answer:
Applications of ultrasound

• Ultrasound can be used in cleaning technology. Minute foreign particles can be removed from objects placed in a liquid bath through which ultrasound is passed.
• Ultrasounds can also be use d to detect cracks and flaws in metal blocks.
• Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
• Ultrasound may be employed to break small ‘stones’ formed in the kidney into fine grains. These grains later get flushed out with urine.

Question 4.
Explain how do SONAR works?
Answer:
SONAR stands for Sound Navigation And Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction, and speed of underwater objects. Sonar consists of Science – 9 (Physics)
a transmitter and a detector and is installed at the bottom of boats and ships. The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector.

The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarines, icebergs etc.

VI. Numerical problems :

Question 1.
The frequency of a source of sound is 600 Hz. Calculate the number of times it vibrates in a minute?
Solution :
Given :
Frequency, v = 600 Hz.
Frequency = Number of vibrations in a second.
Frequency in a minute = Fequency per second × 60
= 600 Hz × 60
No. of vibrations in a minute = 36,000 Hz (or) 36 kHz.

Question 2,.
A stone is dropped from the top of a tower 750 m high into a pond of water at the base of the tower. Calculate the number of seconds for the splash to be heard? (Given g = 10 ms^-2 and speed of sound = 340 m s^-1)
Solution :
Given :
Height of tower, s = 750 m
Acceleration, g =10 ms^-2
Speed of sound, v – 340 ms^-1
Initial velocity of stone, u =0 (stone at rest)

Consider
(i) Time taken to reach the pond, t₁
(ii) Time taken by sound to reach top, t₂
According to Equation of Motion, s = ut + \(\frac{1}{2}\) at²
Here, s = ut₁ + \(\frac{1}{2}\) gt₁²
Substituting the values, 750 = 0 × t₁ + \(\frac{1}{2}\) × 10 × t₁²
750 = 5 t₁²
t₁² = 150
t₁ = 12.25 s
Time taken by sound to reach top t₂ = \(\frac{s}{v}=\frac{750}{340}\) = 2.2s
t₂ = 2.2 s
Time for splash to be heard at top, t = t₁ + t₂
t = 12.25 + 2.2
t = 14.45 s
Time for splash to be heard at top, t = 14.45 s.

Intext Activities

ACTIVITY – 1

Take a tuning fork and strike its prongs on a rubber pad. Bring it near your ear. Do you hear any sound? Now touch the tuning fork with your finger. What do you feel? Do you feel vibrations?

Aim :
To demonstrate the vibration of a molecule.
Materials Required : 1. Tuning fork, 2. Rubber band.

Procedure:

1. Take a tuning fork and strike its prongs on a rubber pad.
2. Bring it near your ear. Hear the sound.
3. Touch the tuning fork with finger.
4. Try to feel the vibrations.

Observation :
When we strike the tuning fork on the rubber pad, it starts vibrating. The vibrations can be felt.

Conclusion :
The tuning fork vibrates the molecules which will vibrate the nearby molecules.
[Vibration = movement of molecule from mean position],

[End of the activity]

ACTIVITY – 2

Take a coil or spring and move it forward and backward. What do you observe? You can observe that in some parts of the coil the turns will be closer and m some other parts the turns will be far apart.
Sound also travels in a medium in the same manner. We will study this now.

Aim :
To demonstrate the propagation of Longitudinal wave. (Sound)
Materials required : 1. Coil, 2. Spring

Procedure:

1. Take a coil or spring
2. Move it forward and backward.

Observations:

1. Some parts of the coil, the turns are closer.
2. In other parts, the turns are far apart.

Conclusion :

1. Closer turns represent compressions.
2. Far apart turns are rarefactions.
3. Longitudinal waves propagate through compressions and rarefactions.

[End of the activity]

ACTIVITY – 3

Listen to the audio of any musical instruments like flute, nathaswaram, tabla, drums, veena etc., Tabulate the differences between the sounds produced by the various sources.

Aim :
To compare the sounds of musical instruments.
Materials required: 1. Flute, 2. Drums, 3. Veena,

Procedure :

1. Hear the instrumental music of flute, drums and veena.
2. Tabulate the difference between the sounds.

Observation :

Conclusion :
Sounds in the different music instruments are characterised by the following qualities such as. 1. Amplitude, 2. The wavelength, 3. Frequency, 4. Pitch, 5. Loudness.

9th Science Guide Sound Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Which of the following is a non-mechanical wave?
(a) sound
(b) water
(c) light
(d) none of the above
Answer:
(c) light

Question 2.
Sound cannot travel through …………………
(a) darkness
(b) gases
(b) vacuum
(d) all of these
Answer:
(c) vacuum

Question 3.
In longitudinal waves, the particle vibrates in a ………………….. direction of propagation.
(a) parallel
(b) perpendicular
(c) curved
(d) all of these
Answer:
(b) perpendicular

Question 4.
Human beings cannot hear …………………
(a) infrasonic sound
(b) sonic sound
(c) ultrasonic sound
(d) a & c
Answer:
(d) a & c

Question 5.
The frequency greater than 20,000 Hz is ………………. sound.
(a) infrasonic
(b) ultrasonic
(c) audible
(d) sonic
Answer:
(b) ultrasonic

Question 6.
of sound depends on the amplitude of the wave,
(a) Loudness
(b) Pitch
(c) Timbre
(d) Tone
Answer:
(a) Loudness

Question 7.
………………. is a general term for the distinguishable characteristic of wave
(a) Pitch
(b) Amplitude
(c) Frequency
(d) Timbre
Answer:
(d) Timbre

Question 8.
Sound travels in air as ……………..wave.
(a) longitudinal
(b) transverse
(c) electromagnetic
(d) all of these
Answer:
(a) longitudinal

Question 9.
The distance between two adjacent crest is called …………………..
(a) amplitude
(b) wavelength
(c) time period
(d) frequency
Answer:
(b) wavelength

Question 10.
When temperature increases the speed of sound
(a) increases
(b) decreases
(c) remains same
(d) none of these
Answer:
(a) increases

Question 11.
The relation between speed, frequency and wavelength is ………………


Answer:
(c) V = γλ

Question 12.
SI unit of wavelength is ……………………………..
(a) Hertz
(b) metre per second
(c) decibel
(d) metre
Answer:
(d) metre

Question 13.
The speed of sound in a gaseous medium depends on …………….
(a) pressure
(b) temperature
(c) density
(d) all of these
Answer:
(d) all of these

Question 14.
The elastic property of medium is a factor of …………. medium.
(a) gas
(b) liquid
(c) solid
(d) none of these
Answer:
(c) solid

Question 15.
To hear an echo, the minimum distance of the obstacle from the source of sound must be ………………
(a) 34 m
(b) 17 m
(c) 340 m
(d) 170 m
Answer:
(b) 17 m

Question 16.
The part of ear that turns pressure variations into electrical signals is .
(a) the hammer
(b) anvil
(c) cochlea
(d) stirrup
Answer:
(c) cochlea

Question 17.
The frequency of source of sound is 60 Hz. Then the number of vibrations in a minute will be ………………..
(a) 36
(b) 360
(c) 3600
(d) 6000
Answer:
(c) 3600

Question 18.
Sonar is a device that uses to measure the distance, direction and speed of the underwater objects.
(a) radio waves
(b) infrared waves
(c) water waves
(d) ultrasonic waves
Answer:
(d) ultrasonic waves

Question 19.
The speeds of sound in four different media are given below. Which of the following is the most likely speed in ms-1 with which the two underwater whales in a sea can talk to each other when separated by a large distance?
(a) 5170
(b) 1280
(c) 340
(d) 1530
Answer:
(d) 1530

[Note = Speed of sound in Sea Water is 1530 ms^-1]

II. Fill in the blanks :

1. The propagating disturbance that travels in a medium is called a ………………
Answer:
Wave

2. Rarefactions are the regions of ……………. where particles are spread apart.
Answer:
low pressure

3. Sound travels faster in ……………. and slower in ……………..
Answer:
Solid, Gas

4. The loudness of sound depends on the ……………. of the sound wave.
Answer:
Intensity

5. A sound of single frequency is called …………….and a collection of tones is called .
Answer:
Tone, Note

6. The speed of sound in air at 0°C is ……………..
Answer:
330 ms^-1

7. …………….is an unwanted sound.
Answer:
Noise

8. Loudness equal to (or) greater than …………….can be painful to the ear.
Answer:
120 dB

9. …………….allows bats to navigate through dark caves and find insects for food.
Answer:
Echolocation

10. …………….is an image obtained by the use of reflected ultrasonic waves.
Answer:
An echogram

11. Depth of an ocean can be determined by …………….
Answer:
SONAR

12. The distance of underwater objects can be deduced by the formula …………….
Answer:
Id = v x t

13. …………….muscle contracts in response to electrical depolarisation of the muscle cells.
Answer:
Cardiac

14. Velocity of sound by a tuning fork frequency of 480 Hz is 340 ms Its wavelength is …………….
Answer:
0.7 m

15. The part of ear that collects the sound from the surroundings is . …………….
Answer:
Pinna

16. Ultrasounds can also be used to detect cracks and flaws in …………….
Answer:
Metal blocks

17. In the inner ear, the pressure variations are turned into electrical signals by the …………….
Answer:
Cochlea

III. Match the following :

I.

Answer:
1-b, 2-c,3-d,4-a

II.

Answer:
1-c, 2-d, 3 -a, 4-b

III.

Answer:
1-c, 2-d,3 -a,4-b

IV. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both Assertion and Reason are true and Reason is the correct explanation of
Assertion. .
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion : Human beings Cannot hear infrasonic sound.
Reason : Sound with frequency less than 20 Hz is called infrasonic sound.
Answer:
(a) Both Assertion and Reason are true and Reason . is the correct explanation of Assertion

Question 2.
Assertion : As the amplitude of sound increases, the loudness of sound decreases.
Reason : The loudness of sound depends on the amplitude of the wave.
Answer:
(d) Assertion is false but reason is true
Correct Assertion : As the amplitude of sound decreases, the loudness of sound decreases.

Question 3.
Assertion : The sound of thunder is heard a little latter than the flash of light.
Reason : The speed of sound is much less than the speed of light.
Answer:
(a) Both Assertion and reason are true and Reason is the correct explanation of Assertion

Question 4.
Assertion : The speed of sound in air is less than speed of sound in solid.
Reason : If we increase the temperature of medium, the speed of sound increases in any medium.
Answer:
(b) Both assertion and reason are true but reason is not the correct explanation of assertion
Reason : The particles in sound are closer in solids than air.

Question 5.
Assertion : The sound which we hear again is called Echo.
Reason : The sensation of sound (Echo) persists in our brain for about 1 s.
Answer:
(c) Assertion is true but reason is false
Reason : The sensation of sound persists in our brain for about 0 – 1 s.

V. State whether true or false. If false, correct the statement:

1. Vibrating particles travel all the way from vibrating object to ear. ,
Answer:
False.
Correct statement: Vibrating particles do not travel all the way from vibrating object to ear.

2. The small to and fro motion is called vibration.
Answer:
True.

3. Pitch is a general term for the distinguishable characteristic of a tone.
Answer:
false.
Correct statement: Timbre is general term for the distinguishable characteristic of a tone.

4. The speed of sound in a gaseous medium depends on the nature of gas.
Answer:
True.

5. The direction of incident sound, direction of reflected sound and the normal are in different Planes.
Answer:
False.
Correct statement: The direction of incident sound, direction of reflected sound and the normal are in same plane.

6. Ultrasonic sounds cannot be heard by the Human beings.
Answer:
True.

7. The Eardrum moves inward when a rarefaction reaches it.
Answer:
False.
Correct statement: The Eardfum moves outward when a rarefaction reaches it.

VI. Very Short Answer questions :

Question 1.
What is a wave?
Answer:
The disturbance which is carried forward in a medium is called wave.

Question 2.
Distinguish between compression and rarefactions.
Answer:
Compression :
Compressions are the regions where particles are crowded together.

Rarefaction :

Rarefactions are the regions of low pressure where particles are spread apart.

Question 3.
Name the five characteristics of’a sound wave. ‘
Answer:
1. Amplitude, 2. Frequency, 3. Time period, 4. Wavelength, 5. Velocity or speed.

Question 4.
Name the distinguishing factors of sound.
Answer:
1. Loudness, 2. Pitch, 3. Timbre (or) quality.

Question 5.
Define : Intensity.
Answer:
Intensity is defined as the amount of energy per unit time perpendicular to the direction of propagation of the wave.

Question 6.
Differentiate tone from note.
Answer:
Tone : A sound of single frequency
Note : A collection of tones.

Question 7.
What is Reverberation?
Answer:
The repeated reflection that results in persistent sound is called reverberation.

Question 8.
Expand the abbreviation of the term SONAR.
Answer:
SONAR – SOUND NAVIGATION AND RANGING.

Question 9.
What type of waves are illustrated by the movement of a rope whose one end is moved up and down?
Answer:

• The movement of rope whose one end is moved up and down is an example of
  Transverse wave.
• The movement of particles of the medium is perpendicular to the direction of
  propagation of the wave is called Transverse Wave.

Question 10.
Name the type of waves produced when a tuning fork is struck in air.
Answer:
Longitudinal waves are produced when a tuning fork is struck in air.

Question 11.
A stone is dropped on the surface of water in a pond. Name the types of waves produced.
Answer:
Transverse waves are produced when a stone is dropped into the pond.

Question 12.
State one observation from every day life which shows that sound travels much more slower than light.
Answer:
The flash of lightening is seen before we hear the sound of thunderstorm.
Reason : The speed of sound (344 m/s) is less than the speed of light (3 × 10⁸ m/s)

Question 13.
What name is given to those air-crafts which fly at speeds greater than the speed of sound?
Answer:
Supersonic Aircraft.

Question 14.
Name the device which is used to produce sound in laboratory experiments.
Answer:
Tuning fork is used to produce sound in laboratory experiments.

Question 15.
What should an object do to produce sound?
Answer:

• An object should vibrate in a medium.
• Vibrations travel as disturbances to reach our ears as sound.

Question 16.
Can sound travel through vacuum?
Answer:

• Sound cannot travel through vacuum.
• Sound needs a material medium to travel like air, water, steel, etc.

VII. Answer in brief :

Question 1.
How do we hear sound?
Answer:

• Mechanical energy vibrates an object.
• The vibrations reach our ear and we hear sound.

Question 2.
Why are sound waves called mechanical waves?
Answer:
Sound waves are called as mechanical waves because sound waves need a medium to propagate and propagation through medium due to interaction of the particles.

Question 3.
Define : (i) Amplitude (ii) Frequency
Answer:
Amplitude (A) : The maximum displacement of the particles of the medium from their original undisturbed position when a wave passes through the medium. Unit: metre (m).
Frequency (n) : The number of vibrations produced in one second is called Frequency of the wave. Unit: Hertz (Hz) or s^-1

Question 4.
Define : Wavelength (λ) and Timbre
Answer:
Wavelength (λ) : The maximum distance in which a sound wave repeats itself (or) In a Sound Wave the distance between the centres of two consecutive compressions (or) two consecutive rarefactions. Unit: metre (m).
Timbre: Timbre is the characteristic which distinguish two sounds of same loudness and pitch of two different instruments.

Question 5.
How are the Wavelength and frequency of a Sound wave related to its speed?
Answer:
Speed (v), Wavelength (λ) and frequency of sound (υ) are related by the following equation: Speed (v) = Wavelength (λ) × Frequency (υ) => v = λ × υ

Question 6.
What are the factors that intensity of Sound depends upon?
Answer:
The intensity of sound depends on the

• Amplitude of the source.
• Distance of the observer from the source.
• Surface area of the source.
• Density of the medium.
• Frequency of the source.

Question 7.
On which factors the speed of sound in gaseous medium depends?
Answer:

• Pressure of the medium.
• Temperature of the medium.
• Density of the medium.
• Nature of the medium.

Question 8.
On which factors the speed of sound in solid medium depends?
Answer:

• Elastic property of the medium.
• Temperature of the medium.
• Density of the medium.

Question 9.
Mention the fequency ranges of infrasoncis and ultrasonics.
Answer:

• Sound waves with frequencies below audible range is termed as Infrasonics.
  Infrasonics: Frequencies less than 20 Hz.
• Sound waves with frequencies above audible range is called as Ultrasonics.
  Ultrasonics: Frequencies greater than 20,000 Hz.

Question 10.
Why is a sound wave called a longitudinal wave?
Answer:
Sound wave is called a Longitudinal wave because

• It produces compressions and rarefactions in the air.
• The particles of air vibrates parallel to the direction of propagation.

Question 11.
Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
The Timbre (or) quality of sound enables us to identify our friend by his voice.

Question 12.
List the causes of noise pollution.
Answer:

• Hearing problems.
• Rupture of eardrum and hearing loss.
• Psychological damages.

Question 13.
Why are roots and walls of the auditorium covered with rough plaster?
Answer:
To reduce the effect of reverberation in large halls of the auditorium.

Question 14.
Give two practical applications of reflection of Sound?
Answer:

• SONAR – Reflection of sound is used to measure the distance, direction and speed of underwater objects.
• Stethoscope – Patient’s heartbeats reach doctor’s ear by multi reflections of sound.

Question 15.
What is acoustics?
Answer:
Acoustics is a branch of physics that deals with the study of properties of Sound.

VIII. Answer in detail :

Question 1.
Prove that sound needs a material medium for its propagation.
Answer:
To prove sound needs a material medium.

• Take an electric bell and an airtight glass jar connected to a vacuum pump.
• Suspend the electric bell inside the airtight jar and press the switch of the bell and hear the sound of the bell.
• Now pump out the air from the glass jar gradually.
• If the jar has vaccum, any sound will not be heard.
• So, sound needs a material medium to travel (here, it is air) and it is proved.

Question 2.
Distinguish between Loudness and Intensity of the Sound?
Answer:
Loudness

1. Loudness is a quantity by virtue of which sound can be distinguished.
2. The loudness of the sound is determined by its amplitude. Loudness a (Amplitude) .

Intensity

1. Intensity of the sound wave is defined as the amount of sound energy passing through unit area per second.
2. The amplitude of sound decides the intensity.

Question 3.
What is an echo? Write the conditions to hear an echo.
Answer:
A repeated sound that is caused by the reflection of sound waves from a surface.

Conditions for echo

• For echo, the time interval between the original sound and reflected sound must be 0.1 s. The sound must go to the obstacle and return to the listener on reflection after 0.1s.
• Total distance covered by the sound from source to the obstacle and reflected to listener must be atleast 340 ms^-1 × 0.1s = 34m.
• So the minimum distance of the obstacle from the source of sound = half of total distance
  \(\frac{34 \mathrm{~m}}{2}\) = 17m.
• This distance will change with the temperature of air.

Question 4.
Explain the working of human ear with diagram.
Answer:
Working of Human Ear
Parts of human ear are (i) outer ear, (ii) middle ear, (iii) inner ear.
(i) Outer ear [Pinna] : It collects the sound from the surroundings and directs towards auditory canal.
(ii) Middle ear : Sound reaches the auditory canal and vibrates the eardrum (or) tympanic membrane, a thin membrane.
Three small bones (hammer, anvil, stirrup) amplify the vibrations, several times. The middle ear transmits the amplified pressure variations to the inner ear.

(iii) Inner ear : (Cochlea) (j) Receives vibrations, (ii) converts them into electrical signals and (iii) they are sent to the Brain thro’ auditory nerve.
The Brain interprets the electrical signals to sound.

IX. Numerical problems :

Question 1.
The frequency of tuning fork is 484 Hz. What is the time period?
Solution :
Frequency of tuning fork, n = 484 Hz.

Question 2.
Velolcity of sound in air is 344 ms^-1 What is the range of wavelength of audible sound?
Solution :
Velocity of sound in air, v = 344 ms^-1
Audible frequency range = 20 – 20,000 Hz
We know V = \(v \lambda \Rightarrow \lambda=\frac{v}{v}\)
When Fequency v = 20Hz
\(\lambda=\frac{344}{20}=17.2 \mathrm{~m}\)
When Frequency, v = 20,000Hz
\(\lambda=\frac{344}{20,000}=0.0172 \mathrm{~m}\)
Range of wavelength of audible Sound = 0.0172 m- 17.2 m

Question 3.
A body vibrates 3000 times in one minute. If the velocity of sound in air 330 ms^-1, find (i) Frequency of vibration (ii) Wavelength.
Solution :
Velocity of sound in air, v = 330 ms^-1
No.of vibrations in a minute = 3000 / minute.
(i) Frequency, (Vibrations produced in one second)

Question 4.
A person is listening to a tone of 400 Hz from a distance of 500 m from the source of sound. What is the time interval between successive compressions from source?
Solution :
Fequency of tone u = 400 Hz.
Time interval between two
successive compressions
from source = Time period of wave.

Time interval between two successive compressions from source = 0.0025 s.

Question 5.
An echo returned in 3s. What is the distance of reflecting surface from the source given that the speed of sound is 330 ms^-1.
Solution :
Speed of sound, v = 330 ms^-1
Time of the echo, t = 3s.
Total distance travelled by the sound 2d = v × t = 330 × 3
2d = 990 m.
2d = Distance from source to reflecting surface + distance from reflecting surface to the listener.
So, distance from the source to reflected surface = \(\frac{\text { Total distance }}{2}\)
= \(\frac{2 d}{2}\)
Distance of the reflecting surface from the source = \(\frac{990}{2}\)
= 495m

Question 6.
Two persons are at opposite ends of a steel rod. One strikes the end of rod with a stone. Find the ratio of time taken by the sound wave in air and in steel to reach the second person. (Sound of speed in steel = 5960 ms^-1, Sound of speed in air = 344 ms^-1)
Solution :
Sound of speed in steel = 5960ms^-1
Sound of speed in air =344ms^-1

Question 7.
A Sound wave travels at a speed of 344 ms^-1. If the wavelength is 1.5 cm, what is the frequency of Wave? Will it be audible?
Solution :
Velocity of soung , v = 344ms^-1
Wavelength of sound. λ = 1.5cm

Audible frequency range = 20 – 20000Hz
So frequency 2,29,333 is not audible.