Ch.5: Acids, Bases & Salts

Acids, Bases and Salts | Class 9 | Science | Chaptert 5 | Maharashtra State Board

Understand the nature of acids, bases, and salts, their reactions, dissociation in water, use of indicators, the concept of pH scale, and real-life examples of neutralization. Learn how substances conduct electricity in solution, explore the role of water of crystallization in crystals, and discover how electrolysis helps in separating elements. Includes experiments, chemical equations, and clear explanations for better understanding.

Questions & Answers

1. Identify the odd one out and justify.

(a) Chloride, nitrate, hydride, ammonium

Odd one: Ammonium

Justification: Others are anions (negatively charged ions); ammonium (NH₄⁺) is a cation (positively charged ion).

(b) Hydrogen chloride, sodium hydroxide, calcium oxide, ammonia

Odd one: Hydrogen chloride

Justification: It is an acid, whereas the others are bases or basic oxides.

(c) Acetic acid, carbonic acid, hydrochloric acid, nitric acid

Odd one: Acetic acid

Justification: It is a weak organic acid; the others are strong mineral (inorganic) acids.

(d) Ammonium chloride, sodium chloride, potassium nitrate, sodium sulphate

Odd one: Ammonium chloride

Justification: It is a salt of a weak base and strong acid (acidic salt); others are neutral salts.

(e) Sodium nitrate, sodium carbonate, sodium sulphate, sodium chloride

Odd one: Sodium carbonate

Justification: It is a basic salt; others are neutral salts.

(f) Calcium oxide, magnesium oxide, zinc oxide, sodium oxide

Odd one: Zinc oxide

Justification: It is an amphoteric oxide (reacts with both acids and bases); others are basic oxides.

(g) Crystalline blue vitriol, crystalline common salt, crystalline ferrous sulphate, crystalline sodium carbonate

Odd one: Crystalline common salt

Justification: It does not contain water of crystallization; others are hydrated salts.

(h) Sodium chloride, potassium hydroxide, acetic acid, sodium acetate

Odd one: Acetic acid

Justification: It is an acid; others are either bases or salts.

2. Write down the changes that will be seen in each instance and explain the reason behind it.

(a) 50 ml water is added to 50 ml solution of copper sulphate

• Change: The blue colour of the solution becomes lighter.

• Reason: Copper sulphate solution is diluted. Colour intensity decreases due to reduced concentration of Cu²⁺ ions.

(b) Phenolphthalein is added to 10 ml NaOH solution

• Change: Solution turns pink.

• Reason: Phenolphthalein turns pink in basic solutions, indicating the presence of hydroxide ions (OH⁻).

(c) Copper filings added to 10 ml dilute nitric acid

• Change: Brown gas (NO₂) is released and a blue solution is formed.

• Reason: Nitric acid reacts with copper, forming copper nitrate (blue solution) and nitrogen dioxide (brown gas).

(d) Litmus paper is added to HCl, then NaOH is added

• Change: Red litmus turns blue after adding NaOH.

• Reason: HCl is acidic (turns litmus red); addition of NaOH neutralizes acid and makes solution basic, changing litmus to blue.

(e) Magnesium oxide added to HCl and to NaOH

• Change:

  • With HCl: Salt solution forms.

  • With NaOH: No visible reaction.

• Reason:

  • MgO is a basic oxide. It reacts with acid (HCl) to form salt and water (neutralization).

  • It does not react with another base (NaOH).

(f) Zinc oxide added to HCl and to NaOH

• Change:

  • With HCl: Salt and water form.

  • With NaOH: Solution forms.

• Reason:

  • ZnO is amphoteric – reacts with both acids and bases.

  • With acid, it forms zinc chloride; with NaOH, it forms sodium zincate.

(g) Dilute HCl added to limestone (CaCO₃)

• Change: Effervescence (bubbling) is seen.

• Reason: Acid reacts with carbonate, producing carbon dioxide gas, calcium chloride, and water.

(h) Blue vitriol (CuSO₄·5H₂O) heated, then water added

• Change: Turns white on heating; turns blue again on adding water.

• Reason: Heating removes water of crystallization (CuSO₄ becomes white); rehydration restores blue colour.

(i) Dilute H₂SO₄ taken in electrolytic cell, current passed

• Change: Gas bubbles form at electrodes—hydrogen at cathode, oxygen at anode.

• Reason: Electrolysis of water takes place. H₂ is released at negative electrode, O₂ at positive electrode.

3. Classify the following oxides into three types and name the types.

CaO, MgO, CO₂, SO₃, Na₂O, ZnO, Al₂O₃, Fe₂O₃

Ans.

Basic Oxides

These are metal oxides that react with acids to form salt and water.

• CaO (Calcium oxide)

• MgO (Magnesium oxide)

• Na₂O (Sodium oxide)

Acidic Oxides

These are non-metal oxides that react with bases to form salt and water.

• CO₂ (Carbon dioxide)

• SO₃ (Sulphur trioxide)

Amphoteric Oxides

These oxides react with both acids and bases.

• ZnO (Zinc oxide)

• Al₂O₃ (Aluminium oxide)

• Fe₂O₃ (Ferric oxide)

4. Explain by drawing a figure of the electronic configuration.

a. Formation of sodium chloride from sodium and chlorine.

Ans.

Explanation:

• Sodium (Na) has electronic configuration 2,8,1 and loses 1 electron to form Na⁺ (2,8).

• Chlorine (Cl) has electronic configuration 2,8,7 and gains 1 electron to form Cl⁻ (2,8,8).

• This electron transfer forms an ionic bond, resulting in NaCl.

b. Formation of a magnesium chloride from magnesium and chlorine.

Ans.

Explanation:

• Magnesium (Mg) has configuration 2,8,2 and loses 2 electrons to become Mg²⁺ (2,8).

• Two Chlorine atoms (Cl), each with configuration 2,8,7, gain 1 electron each to form two Cl⁻ ions (2,8,8).

• This results in the ionic compound MgCl₂ with strong electrostatic attraction.

5. Show the dissociation of the following compounds on dissolving in water, with the help of chemical equation and write whether the proportion of dissociation is small or large.

Hydrochloric acid, Sodium chloride, Potassium hydroxide, Ammonia, Acetic acid, Magnesium chloride, Copper sulphate.

Ans.

1. Hydrochloric acid (HCl)

Equation:

HCl (aq) → H⁺ (aq) + Cl⁻ (aq)

Proportion of dissociation: Large (Strong acid)

2. Sodium chloride (NaCl)

Equation:NaCl (aq) → Na⁺ (aq) + Cl⁻ (aq)

Proportion of dissociation: Large (Salt)

3. Potassium hydroxide (KOH)

Equation:KOH (aq) → K⁺ (aq) + OH⁻ (aq)

Proportion of dissociation: Large (Strong base)

4. Ammonia (NH₃)

Equation:NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)

Proportion of dissociation: Small (Weak base)

5. Acetic acid (CH₃COOH)

Equation:CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)

Proportion of dissociation: Small (Weak acid)

6. Magnesium chloride (MgCl₂)

Equation:MgCl₂ (aq) → Mg²⁺ (aq) + 2Cl⁻ (aq)

Proportion of dissociation: Large (Salt)

7. Copper sulphate (CuSO₄)

Equation:CuSO₄ (aq) → Cu²⁺ (aq) + SO₄²⁻ (aq)

Proportion of dissociation: Large (Salt)

6. Write down the concentration of each of the following solutions in g/L and mol/L.

a. 7.3g HCl in 100ml solution

Ans.

• Volume = 100 mL = 0.1 L

• g/L = 7.3 / 0.1 = 73 g/L

• mol/L = 7.3 / (36.5 × 0.1) = 7.3 / 3.65 = 2 mol/L

b. 2g NaOH in 50ml solution

Ans.

• Volume = 0.05 L

• g/L = 2 / 0.05 = 40 g/L

• mol/L = 2 / (40 × 0.05) = 2 / 2 = 1 mol/L

c. 3g CH₃COOH in 100ml solution

Ans.

• Volume = 0.1 L

• g/L = 3 / 0.1 = 30 g/L

• mol/L = 3 / (60 × 0.1) = 3 / 6 = 0.5 mol/L

d. 4.9g H₂SO₄ in 200ml solution

Ans.

• Volume = 0.2 L

• g/L = 4.9 / 0.2 = 24.5 g/L

• mol/L = 4.9 / (98 × 0.2) = 4.9 / 19.6 = 0.25 mol/L

7. Answer the following questions.

a. Classify the acids according to their basicity and give one example of each type.

Basicity of an acid is the number of H⁺ ions released by one molecule of the acid.

Ans.

1. Monobasic acid – Gives 1 H⁺ ion  Example: HCl (Hydrochloric acid)

2. Dibasic acid – Gives 2 H⁺ ions  Example: H₂SO₄ (Sulphuric acid)

3. Tribasic acid – Gives 3 H⁺ ions  Example: H₃PO₄ (Phosphoric acid)

b. What is meant by neutralization? Give two examples from everyday life of the neutralization reaction.

Ans.

Neutralization is a chemical reaction in which an acid reacts with a base to form salt and water.

General reaction: Acid + Base → Salt + Water

Examples from everyday life:

1. Using antacid tablets (base) to relieve acidity caused by excess HCl in the stomach.

2. Using lime (calcium hydroxide) to reduce the acidity of soil.

c. Explain what is meant by electrolysis of water. Write the electrode reactions and explain them.

Ans.

Electrolysis of water is the process of decomposing water (H₂O) into hydrogen gas and oxygen gas using electric current.

Cathode reaction (reduction): 2H₂O (l) + 2e⁻ → H₂ (g) + 2OH⁻ (aq)

Anode reaction (oxidation): 2H₂O (l) → O₂ (g) + 4H⁺ (aq) + 4e⁻

Explanation:

• At the cathode (negative electrode), water molecules gain electrons to form hydrogen gas.

• At the anode (positive electrode), water molecules lose electrons to form oxygen gas.

• The overall reaction breaks down water into its elements: 2H₂O → 2H₂ + O₂

8. Write the chemical equations for the following activities.

(a) NaOH solution was added to HCl solution.

Ans.

Reaction Type: Neutralization

Equation:

NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

(b) Zinc dust was added to dilute H₂SO₄.

Ans.

Reaction Type: Metal + Acid → Salt + Hydrogen gas

Equation:

Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)

(c) Dilute nitric acid was added to calcium oxide.

Ans.

Reaction Type: Acid + Metal oxide → Salt + Water

Equation:

CaO (s) + 2HNO₃ (aq) → Ca(NO₃)₂ (aq) + H₂O (l)

(e) Carbon dioxide gas was passed through KOH solution.

Ans.

Reaction Type: Acidic oxide + Base → Salt + Water

Equation:

CO₂ (g) + 2KOH (aq) → K₂CO₃ (aq) + H₂O (l)

(f) Dilute HCl was poured on baking soda. (NaHCO₃).

Reaction Type: Acid + Metal bicarbonate → Salt + CO₂ + Water

Equation:

NaHCO₃ (s) + HCl (aq) → NaCl (aq) + CO₂ (g) + H₂O (l)

9. State the differences.

a. Acids and bases

Acids	Bases
Substances that give H⁺ ions in water	Substances that give OH⁻ ions in water
Taste sour	Taste bitter and feel soapy
Turn blue litmus red	Turn red litmus blue
Examples: HCl, H₂SO₄, CH₃COOH	Examples: NaOH, Ca(OH)₂, NH₄OH

b. Cation and anion

Cation	Anion
Positively charged ion (+)	Negatively charged ion (−)
Formed by loss of electrons	Formed by gain of electrons
Moves towards cathode	Moves towards anode
Examples: Na⁺, Ca²⁺, NH₄⁺	Examples: Cl⁻, SO₄²⁻, NO₃⁻

c. Negative electrode and positive electrode.

Negative Electrode (Cathode)	Positive Electrode (Anode)
Connected to negative terminal of battery	Connected to positive terminal of battery
Attracts cations	Attracts anions
Reduction occurs (gain of electrons)	Oxidation occurs (loss of electrons)
Hydrogen gas forms here (in electrolysis)	Oxygen gas forms here (in electrolysis)

10. Classify aqueous solutions of the following substances according to their pH into three groups : 7, more than 7, less than 7.

Common salt, sodium acetate, hydrochloric acid, carbon dioxide, potassium bromide, calcium hydoxide, ammonium chloride, vinegar, sodium carbonate, ammonia, sulphur dioxide.

Ans.

pH = 7 (Neutral Solution)

• Common salt (Sodium chloride – NaCl)

• Potassium bromide (KBr)

pH < 7 (Acidic Solution)

• Hydrochloric acid (HCl)

• Carbon dioxide (CO₂ – forms carbonic acid in water)

• Ammonium chloride (NH₄Cl – salt of strong acid & weak base)

• Vinegar (contains acetic acid – CH₃COOH)

• Sulphur dioxide (SO₂ – forms sulphurous acid in water)

pH > 7 (Basic / Alkaline Solution)

• Sodium acetate (CH₃COONa – salt of weak acid & strong base)

• Calcium hydroxide [Ca(OH)₂]

• Sodium carbonate (Na₂CO₃)

• Ammonia (NH₃)

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E X T R A

Intext Questions and Answers

1. Select the correct option

1. …………………. acid is present in lemon.

(a) malic acid

(b) tartaric acid

(c) citric acid

(d) butyric acid

Ans.

Citric acid is present in lemon.

2. Tamarind contains …………………. acid.

(a) Lactic acid

(b) tartaric acid

(c) matlic acid

(d) butyric acid

Ans.

Tamarind contains tartaric acid.

3. Butter milk contains …………………. acid.

(a) butyric acid

(b) Lactic acid

(c) matlic acid

(d) citric acid

Ans.

Buttermilk contains lactic acid.

4. If the basic radical is H+ the type of compound is ………………… .

(a) neutral

(b) base

(c) acid

(d) alkali

Ans.

If the basic radical is H+, the type of compound is acid.

5. The name of compound NH₃ is ………………… .

(a) nitric acid

(b) ammonium

(c) nitride

(d) ammonia

Ans.

The name of compound NH₃ is ammonia.

6. The bases which are soluble in water are called as ………………… .

(a) indicators

(b) acids

(c) alkalis

(d) salts

Ans.

The bases which are soluble in water are called as alkalis.

7. H₃PO₄ is a …………………. acid.

(a) monobasic

(b) tribasic

(c) tetrabasic

(d) dibasic

Ans.

H₃PO₄ is a tribasic acid.

8. According to pH scale pure water has a pH of ………………… .

(a) 6

(b) 7

(c) 5

(d) 8

Ans.

According to pH scale, pure water has a pH of 7.

9. With reference to neutralization, metallic oxides are ………………… in nature.

(a) basic

(b) neutral

(c) acidic

(d) saline

Ans.

With reference to neutralization, metallic oxides are basic in nature.

10. Molecular formula of blue vitriol is ………………… .

(a) CuSO₃·5H₂O

(b) CuSO₄·4H₂O

(c) CuSO₃·4H₂O

(d) CuSO₄·5H₂O

Ans. 

Molecular formula of blue vitriol is CuSO₄·5H₂O

11. Molecular formula of crystalline alum is ………………… .

(a) KSO₄, AlSO₄, 24H₂O

(b) K₂SO₄, AlSO₄, 24H₂O

(c) K₂SO₄·Al₂(SO₄)₃·24H₂O

(d) KSO₄, Al₂(SO₄)₃, 24H₂O

Ans. 

Molecular formula of crystalline alum is K₂SO₄·Al₂(SO₄)₃·24H₂O

12. Molecular formula for sodium oxide is ………………… .

(a) Na₂O

(b) NaO₂

(c) NaO

(d) Na₂O₂

Ans. 

Molecular formula for sodium oxide is Na₂O

13. H₂CO₃ is …………………. acid.

(a) monobasic

(b) dibasic

(c) tribasic

(d) tetrabasic

Ans. 

H₂CO₃ is a dibasic acid.

14. Molecular formula of red oxide is ………………… .

(a) Fe₂O₃

(b) CuO

(c) Fe₃O₄

(d) Na₂O

Ans. 

Molecular formula of red oxide is Fe₂O₃

15. The positive terminal electrode is called as ………………… .

(a) anode

(b) cathode

(c) anion

(d) cation

Ans.

The positive terminal electrode is called anode.

16. …………………. produced in stomach helps in digestion.

(a) Hydrochloric acid

(b) Oxalic acid

(c) Sulphuric acid

(d) Nitric acid

Ans.

Hydrochloric acid produced in stomach helps in digestion.

17. The solution turns blue litmus red, its pH is likely to be ………………… .

(a) 7

(b) 4

(c) 14

(d) 9

Ans.

The solution turns blue litmus red, its pH is likely to be 4.

18. An ionic compound NaCl is formed by ………………… .

(a) Na+ and Cl–

(b) Na+ and Cl+

(c) Na– and Cl–

(d) Na– and Cl+

Ans.

An ionic compound NaCl is formed by Na+ and Cl-.

19. pH of strong acid is ………………… .

(a) 0

(b) 7

(c) 8

(d) 14

Ans.

pH of strong acid is 0.

20. HCl + NaOH → NaCl + H₂O is a …………………. reaction.

(a) neutralization

(b) crystallisation

(c) electrolysis

(d) dissociation

Ans. 

HCl + NaOH → NaCl + H₂O is a neutralization reaction.

21. Adding water to acid is an …………………. reaction.

(a) endothermic

(b) exothermic

(c) neutralisation

(d) crystallisation

Ans.

Adding water to acid is an exothermic reaction.

2. Find the odd one out with reason in short.

(a) Rose Petal, Turmeric, Phenolphthalein, Indigo.

Ans.

Rose Petal – Others are indicators, rose petal is not a common acid-base indicator.

(b) Lime water, Vinegar, Acetic acid, Tartaric acid.

Ans.

Lime water – Others are acids, lime water is basic.

(c) NaHCO₃, HCl, H₂SO₄, HNO₃

Ans. 

NaHCO₃ – It's a salt, others are acids.

(d) Oxalic acid, Nitric acid, Citric acid, acetic acid.

Ans.

Nitric acid – It's a mineral acid, others are organic acids.

(e) Crystalline, Liquid, Gases, Solid.

Ans.

Crystalline – Others are states of matter, crystalline is a structure.

(f) Ca(OH)₂, Mg(OH)₂, NaOH, NH₄OH

Ans. 

NaOH – It's a strong base, others are weak bases.

3. Name the following:

1. Name the three types of ionic compounds.

Ans.

Acids, Bases, Salts

2. Name the two constituents of molecule of an ionic compound.

Ans.

Cation and Anion

3. Name any three acids with their molecular formula.

Ans. 

HCl (Hydrochloric acid), H₂SO₄ (Sulphuric acid), HNO₃ (Nitric acid)

4. Name any three bases with their molecular formula.

Ans. 

NaOH (Sodium hydroxide), KOH (Potassium hydroxide), Ca(OH)₂ (Calcium hydroxide)

5. Name any three salts with their molecular formula.

Ans. 

NaCl (Sodium chloride), KNO₃ (Potassium nitrate), CaCO₃ (Calcium carbonate)

6. Name any two strong acids.

Ans. 

HCl, H₂SO₄

7. Name any two weak acids.

Ans. 

CH₃COOH, H₂CO₃

8. Name any two strong bases.

Ans. 

NaOH, KOH

9. Name a weak base.

Ans. 

NH₄OH

10. Name any two alkalis.

Ans. 

NaOH, KOH

11. Name any two acids with their basicity 1 (monobasic).

Ans. 

HCl, HNO₃

12. Name any two acids with their basicity 2 (dibasic).

Ans. 

H₂SO₄, H₂CO₃

13. Name any two acids with their basicity 3 (tribasic).

Ans. 

H₃PO₄, H₃BO₃

14. Name any two bases with their acidity 1 (monoacidic).

Ans. 

NaOH, KOH

15. Name any two bases with their acidity 2 (diacidic).

Ans. 

Ca(OH)₂, Ba(OH)₂

16. Name any two bases with their acidity 3 (triacidic).

Ans.

 Al(OH)₃, Fe(OH)₃

17. Name the two units to express the concentration of the solution.

Ans.

g/L and mol/L

4. State whether the following statements are true or false and if false. Correct the false statement:

(1) The separation of H and Cl in HCl is in absence of water.

Ans. 

False – Separation of H and Cl in HCl occurs in the presence of water.

(2) NaOH(s) + Water → Na⁺(aq) + OH⁻(aq)

Ans.

True

(3) H₂SO₄ is a strong acid.

Ans. 

True

(4) NaCl is an ionic compound.

Ans.

True

(5) Turmeric is synthetic indicator.

Ans.

Turmeric is a natural indicator.

(6) Metal + Dilute acid forms salt and water.

Ans.

Metal + Dilute acid forms salt and hydrogen gas.

(7) Copper oxide is called red primer.

Ans.

True

(8) Oxide of non-metal + Acid → Salt + Water.

Ans.

True

(9) Zinc oxide reacts with sodium hydroxide to form sodium zincate.

Ans.

True

(10) Al₂O₃ is an amphoteric oxide.

Ans. 

True

(11) Blue vitriol – ZnSO₄·7H₂O.

Ans. 

False – Blue vitriol is CuSO₄·5H₂O

(12) Molecular formula for crystalline ferrous sulphate is Fe₅O₄·5H₂O.

Ans. 

False – Ferrous sulphate is FeSO₄·7H₂O

(13) NaCl in water does not conduct electricity.

Ans.

False – NaCl in water does conduct electricity.

(14) Phenolphthalein is colourless in base.

Ans.

False – Phenolphthalein is pink in base.

5. Define the following:

1. Acid

Ans.

A substance that gives H⁺ ions in aqueous solution.

2. Base

Ans.

A substance that gives OH⁻ ions in aqueous solution.

3. Strong Acid

Ans.

An acid that dissociates completely in water.

4. Weak Acid

Ans.

An acid that partially dissociates in water.

5. Strong Base

Ans.

A base that dissociates completely in water.

6. Weak Base

Ans.

A base that partially dissociates in water.

7. Alkali

Ans.

A base that is soluble in water.

8. Basicity of acids

Ans.

Number of H⁺ ions released per molecule.

9. Acidity of bases

Ans.

Number of OH⁻ ions released per molecule.

10. Concentrated solution.

Ans.

Amount of solute present in a given amount of solution.

11. Dilute solution

Ans.

A solution having a small amount of solute.

12. Neutralization

Ans.

A reaction between acid and base to form salt and water.

13. Cathode

Ans.

Negative electrode where reduction occurs.

14. Anode

Ans.

Positive electrode where oxidation occurs.

15. Cations

Ans.

Positively charged ions.

16. Anions

Ans.

Negatively charged ions.

17. Electrolytic cell

Ans.

Setup used for electrolysis.

18. Molarity of a solution

Ans.

Number of moles of solute per litre of solution.

19. Acid – base indicators

Ans.

Substances that change colour in acidic or basic solutions.

6. Explain the following chemical reactions with the help of balanced equations:

1. Magnesium reacts with dilute hydrochloric acid.

Ans.

Mg + 2HCl → MgCl₂ + H₂↑

2. When copper reacts with nitric acid.

Ans.

3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O

3. When ferric oxide reacts with diluted hydrochloric acid.

Ans.

Fe₂O₃ + 6HCl → 2FeCl₃ + 3H₂O

4. When calcium oxide reacts with dilute hydrochloric acid.

Ans.

CaO + 2HCl → CaCl₂ + H₂O

5. When Magnesium oxide reacts with dilute hydrochloric acid.

Ans.

MgO + 2HCl → MgCl₂ + H₂O

6. When zinc oxide reacts with dilute hydrochloric acid.

Ans.

ZnO + 2HCl → ZnCl₂ + H₂O

7. When aluminium oxide reacts with hydrogen fluoride

Ans.

Al₂O₃ + 6HF → 2AlF₃ + 3H₂O

8. When carbon dioxide reacts with sodium hydroxide.

Ans.

CO₂ + 2NaOH → Na₂CO₃ + H₂O

9. When carbon dioxide reacts with potassium hydroxide.

Ans.

CO₂ + 2KOH → K₂CO₃ + H₂O

10. When sulphur trioxide reacts with sodium hydroxide.

Ans.

SO₃ + 2NaOH → Na₂SO₄ + H₂O

11. When calcium hydroxide reacts with carbon dioxide.

Ans.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

12. When sodium carbonate reacts with hydrochloric acid.

Ans.

Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O

13. When sodium carbonate reacts with sulphuric acid.

Ans.

Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O

14. When calcium carbonate reacts with nitric acid.

Ans.

CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + CO₂ + H₂O

15. When potassium carbonate reacts with sulphuric acid.

Ans.

K₂CO₃ + H₂SO₄ → K₂SO₄ + CO₂ + H₂O

16. When sodium bicarbonate reacts with hydrochloric acid. OR Dilute HCl was poured on baking soda

Ans.

NaHCO₃ + HCl → NaCl + CO₂ + H₂O

17. When potassium bicarbonate reacts with nitric acid.

Ans.

KHCO₃ + HNO₃ → KNO₃ + CO₂ + H₂O

18. When sodium bicarbonate reacts with acetic acid.

Ans.

NaHCO₃ + CH₃COOH → CH₃COONa + CO₂ + H₂O

19. When copper sulphate is heated.

Ans.

CuSO₄·5H₂O → CuSO₄ + 5H₂O (on heating)

20. When Ferrous sulphate is heated.Ans.

FeSO₄·7H₂O → Fe₂O₃ + SO₂ + SO₃ + H₂O (on heating)

7. Give scientific reasons:

1. Ionic compound NaCl has very high stability.

Reason:

NaCl is formed by the transfer of one electron from a sodium atom to a chlorine atom, resulting in the formation of Na⁺ and Cl⁻ ions. These oppositely charged ions are held together by a strong electrostatic force called the ionic bond. Also, both ions achieve a stable octet configuration, which contributes to high stability of NaCl.

2. Ionic compound dissociates while forming an aqueous solution.

Reason:

When an ionic compound like NaCl dissolves in water, the water molecules surround the ions and weaken the electrostatic force between them. This causes the ions to separate (dissociate) and disperse uniformly in the solution as Na⁺(aq) and Cl⁻(aq).

3. Blue coloured copper sulphate crystals become colourless on heating.

Reason:

Blue vitriol (CuSO₄·5H₂O) contains water of crystallisation responsible for its blue colour. On heating, it loses this water and becomes anhydrous copper sulphate (CuSO₄), which is a white powder. This is a physical change, not chemical.CuSO₄·5H₂O → CuSO₄ + 5H₂O

4. During electrolysis of water, a few drops of sulphuric acid are added to it.

Reason:

Pure water is a poor conductor of electricity due to the very low concentration of H⁺ and OH⁻ ions. Adding sulphuric acid increases the concentration of ions, making the solution a better conductor, which is essential for electrolysis to occur.

5. Glucose is a non-electrolyte.

Reason:

Glucose (C₆H₁₂O₆) does not dissociate into ions in water. As it doesn’t produce free ions, it does not conduct electricity, and hence is considered a non-electrolyte.

6. Pure water is a poor conductor of electricity but aqueous solution of sodium chloride conducts electricity.

Reason:

Pure water has very few H⁺ and OH⁻ ions, so it cannot carry electric current efficiently. However, when NaCl dissolves in water, it dissociates completely into Na⁺ and Cl⁻ ions, which are charge carriers that allow electricity to pass.

7. When carbon dioxide gas is passed through freshly prepared lime water, the limewater turns milky.

Reason:

CO₂ reacts with limewater [Ca(OH)₂] to form calcium carbonate (CaCO₃), which is insoluble and appears as a milky white precipitate.Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O

8. Answer the following:

1. Write down chemical equations for:

(a) Zinc oxide reacts with sodium hydroxide

Equation:

ZnO + 2NaOH → Na₂ZnO₂ + H₂O

(Sodium zincate is formed along with water)

(b) Aluminium oxide reacts with sodium hydroxide

Equation:

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

(Sodium aluminate is formed along with water)

2. Can we call Al₂O₃ and ZnO acidic oxides on the basis of the above reactions?

Ans.

No, we cannot call Al₂O₃ and ZnO acidic oxides.They react with both acids and bases, which means they show both acidic and basic properties. Therefore, they are not purely acidic. Such oxides are called amphoteric oxides.

3. Define ‘amphoteric oxides’ and give two examples.

Definition:

Amphoteric oxides are metallic oxides that react with both acids and bases to form salt and water.

Examples:

• Al₂O₃ (Aluminium oxide)

• ZnO (Zinc oxide)

9. Answer in brief:

1. What are acids, bases and salts?

Ans.

• Acids are substances that give H⁺ ions when dissolved in water.Example: HCl, H₂SO₄

• Bases are substances that give OH⁻ ions when dissolved in water.Example: NaOH, Ca(OH)₂

• Salts are ionic compounds formed by the neutralization reaction between an acid and a base.Example: NaCl, K₂SO₄

2. What is an ionic bond?

Ans.

An ionic bond is the electrostatic force of attraction between a positively charged ion (cation) and a negatively charged ion (anion).Example: In NaCl, Na⁺ and Cl⁻ ions are held together by an ionic bond.

3. Give examples to show that proportions of H⁺ and OH⁻ ions in aqueous solution determine the properties of those solutions.

Ans.

• Acidic solution: Lemon juice has more H⁺ ions → pH ≈ 2.5

• Neutral solution: Pure water has equal H⁺ and OH⁻ ions → pH = 7

• Basic solution: Lime water has more OH⁻ ions → pH ≈ 10.5

The greater the H⁺ ion concentration, the more acidic the solution; the greater the OH⁻ ion concentration, the more basic the solution.

4. What is pH scale?

Ans.

The pH scale is a numerical scale from 0 to 14 used to express the concentration of H⁺ ions in an aqueous solution:

• pH < 7 → Acidic solution

• pH = 7 → Neutral solution

• pH > 7 → Basic solution

It was introduced by Søren Sørensen in 1909.

5. Give the pH of following solutions:

Solution	pH
1M HCl (strong acid)	0.0
Lemon juice	2.5
Pure water	7.0
Baking soda solution	8.5
Milk of magnesia	10.5
1M NaOH (strong base)	14.0

6. What is universal indicator? Which is the most accurate method of measuring the pH of a solution?

Ans.

• A universal indicator is a mixture of several indicators that shows different colours at different pH values, helping identify if a solution is acidic, basic, or neutral.

• The most accurate method to measure pH is by using a pH meter, an electronic device that gives precise numerical pH values.

10. Answer in detail:

1. Explain the Arrhenius theory of acids and bases.

Ans.

According to Arrhenius theory (proposed by Svante Arrhenius in 1887):

• Acid is a substance that gives H⁺ (hydrogen ion) when dissolved in water.Example: HCl → H⁺ + Cl⁻

• Base is a substance that gives OH⁻ (hydroxide ion) when dissolved in water.Example: NaOH → Na⁺ + OH⁻

This theory explains the acidic or basic nature of substances based on ion formation in water.

2. Write a short note on Neutralization.

Ans.

Neutralization is a chemical reaction between an acid and a base that forms a salt and water.It occurs due to the reaction of H⁺ ions from the acid with OH⁻ ions from the base.

General equation:HCl + NaOH → NaCl + H₂O

• Acid + Base → Salt + WaterThis reaction is used in medicine (antacids), agriculture (soil treatment), and daily life.

3. Explain the water of Crystallization.

Ans.

Water of crystallization is the fixed number of water molecules present in the structure of certain crystalline compounds.

• These water molecules are chemically bonded and are part of the crystal's structure.

• On heating, the compound loses this water and changes appearance (usually becomes white).

Example:CuSO₄·5H₂O (blue vitriol)On heating:CuSO₄·5H₂O → CuSO₄ (white) + 5H₂O

This is a physical change and reversible by adding water.

4. Explain the conduction of electricity through solutions of ionic compounds.

Ans.

• Ionic compounds like NaCl, H₂SO₄, or CuSO₄ conduct electricity in aqueous (water) solution or in molten state.

• This happens because ions are free to move in these states.

• Positive ions (cations) move to the negative electrode (cathode), andNegative ions (anions) move to the positive electrode (anode).

This flow of ions completes the circuit and allows electric current to pass.Example: NaCl (solid) does not conduct, but NaCl(aq) does.

This process is called electrolysis.

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