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

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:

Hydrated	Anhydrous
1. Hydrons is a term used to explain a substance that contains water as a constituent	Anhydrous is a term used to explain a substance that does not contain water as a constituent.
2. Composed of water molecules.	Not composed of water molecules.
3. These are known as hydrates.	Known as anhydrates
4. Hydroscopic compounds can form hydrous compounds by Absorption of water from the air.	Anhydrous compounds can absorb water from the air.
Ex : CuSO4 5H2O – Blue vitrol.	Ex: NaCl

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.

Source	Acid present
1) Apple	?
2) ?	Citric acid
3) ?	tartaric acid
4) Tomato	?
5) Vinegar	?

Answer:

Source	Acid present
1) Apple	Malic acid
2) Lemon	Citric acid
3) Grapes	tartaric acid
4) Tomato	Oxalic acid
5) Vinegar	Acetic acid

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.

1) Hydrochloric acid	a) Fertilizer
2) Citric acid	b) Baking powder
3) Nitric acid	c) Car batteries
4) Oxalic acid	d) Cleansing agent in toilets
5) Sulphuric acid	e) Removing black stains
	f) Effervescent salts

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

Question 4.

1) Hardest substance in our body	a) Aluminium phosphate
2) Citrus fruits	b) Potash alum
3) Rice plant	c) Insoluble in water
4) Double salts	d) Acidic soil
5) Silver chloride	e) Calcium phophate
	f) Alkaline soil

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.