CLASS 10 SCIENCE : CHAPTER 2 — ACIDS, BASES AND SALTS
Question Bank
Question types included:
- MCQs
- Assertion–Reason
- Fill in the blanks
- True/False
- Match the columns
- Very Short Answer
- Short Answer
- Give Reason
- Chemical Equation Questions
- Reaction Completion
- Case-Based Questions
- Application-Based Questions
- Competency-Based Questions
- Numerical/Logical Questions
- Diagram/Activity-Based Questions
- Long Answer Questions
- HOTS Questions
- Integrated Revision Questions
SECTION A — MULTIPLE CHOICE QUESTIONS
Choose the correct option.
1. Which ion is mainly responsible for the acidic character of an aqueous solution?
A. Na⁺
B. OH⁻
C. H₃O⁺
D. Cl⁻
2. A solution turns red litmus paper blue. Its pH is most likely:
A. 2
B. 5
C. 7
D. 10
3. Which substance is an alkali?
A. CuO
B. NaOH
C. CuCO₃
D. CO₂
4. Phenolphthalein generally becomes ______ in a basic solution.
A. red
B. blue
C. pink
D. yellow
5. Methyl orange shows a ______ colour in an acidic medium.
A. yellow
B. red
C. blue
D. pink
6. Which of the following is an olfactory indicator?
A. Litmus
B. Turmeric
C. Vanilla essence
D. Phenolphthalein
7. When zinc reacts with dilute sulphuric acid, the gas evolved is:
A. oxygen
B. carbon dioxide
C. hydrogen
D. chlorine
8. The correct general reaction for an acid with a metal is:
A. Acid + Metal → Base + Hydrogen
B. Acid + Metal → Salt + Hydrogen
C. Acid + Metal → Salt + Oxygen
D. Acid + Metal → Water + Carbon dioxide
9. Which gas turns lime water milky?
A. H₂
B. O₂
C. CO₂
D. N₂
10. An acid reacting with a metal carbonate produces:
A. salt + hydrogen
B. salt + carbon dioxide + water
C. salt + oxygen + water
D. base + carbon dioxide
11. Which is a neutralisation reaction?
A. Zn + H₂SO₄ → ZnSO₄ + H₂
B. NaOH + HCl → NaCl + H₂O
C. NaHCO₃ + HCl → NaCl + H₂O + CO₂
D. CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
12. The reaction between an acid and a base is called:
A. displacement
B. decomposition
C. neutralisation
D. oxidation
13. Which is a basic oxide?
A. CO₂
B. SO₂
C. CuO
D. NO₂
14. Non-metallic oxides are generally:
A. basic
B. acidic
C. neutral only
D. metallic
15. Which substance produces OH⁻ ions in aqueous solution?
A. HCl
B. H₂SO₄
C. NaOH
D. CH₃COOH
16. Which substance does NOT show acidic character merely because it contains hydrogen?
A. HCl
B. H₂SO₄
C. Glucose
D. HNO₃
17. Acidic solutions conduct electricity because they contain:
A. only water molecules
B. ions
C. neutral atoms only
D. gases
18. Dry HCl gas does not change dry blue litmus because:
A. HCl is not an acid
B. litmus is inactive
C. water is needed for formation of H₃O⁺ ions
D. HCl contains no hydrogen
19. Which ion is produced when NaOH dissolves in water?
A. H⁺
B. OH⁻
C. Cl⁻
D. CO₃²⁻
20. The pH of a neutral solution is:
A. 0
B. 5
C. 7
D. 14
21. A solution with pH 2 is:
A. strongly acidic
B. weakly acidic
C. neutral
D. basic
22. A solution with pH 12 is:
A. acidic
B. neutral
C. basic
D. weakly acidic
23. As hydronium ion concentration increases, pH:
A. increases
B. decreases
C. remains exactly 7
D. becomes zero in every case
24. Which has the highest H₃O⁺ concentration?
A. pH 2
B. pH 5
C. pH 7
D. pH 9
25. Which solution is the most alkaline?
A. pH 8
B. pH 10
C. pH 12
D. pH 7
26. Which is considered a strong acid in the chapter’s comparison?
A. Acetic acid
B. Hydrochloric acid
C. Carbonic acid
D. None
27. Acid rain is rainwater having pH:
A. above 7
B. exactly 7
C. below 5.6
D. above 10
28. Tooth decay becomes a concern when the pH of the mouth falls below approximately:
A. 3.5
B. 5.5
C. 7.5
D. 9.5
29. Which substance is used as an antacid?
A. Magnesium hydroxide
B. Hydrochloric acid
C. Sulphuric acid
D. Nitric acid
30. The acid naturally present in vinegar is:
A. citric acid
B. lactic acid
C. acetic acid
D. methanoic acid
31. The acid associated with an ant sting is:
A. citric acid
B. methanoic acid
C. tartaric acid
D. lactic acid
32. The acid present in curd is:
A. acetic acid
B. oxalic acid
C. lactic acid
D. tartaric acid
33. Common salt is:
A. NaOH
B. NaCl
C. NaHCO₃
D. Na₂CO₃
34. Brine is an aqueous solution of:
A. sodium hydroxide
B. sodium chloride
C. calcium chloride
D. sodium carbonate
35. The electrolysis of brine is called the:
A. Solvay process
B. chlor-alkali process
C. neutralisation process
D. crystallisation process
36. Which product is formed during the chlor-alkali process?
A. NaOH
B. H₂SO₄
C. CaCO₃
D. CuSO₄
37. During electrolysis of brine, chlorine gas is released at the:
A. cathode
B. anode
C. salt bridge
D. solution surface
38. During the chlor-alkali process, hydrogen gas is released at the:
A. anode
B. cathode
C. both electrodes equally
D. neither electrode
39. Baking soda is:
A. Na₂CO₃·10H₂O
B. NaHCO₃
C. NaCl
D. CaSO₄·2H₂O
40. Washing soda is:
A. NaHCO₃
B. Na₂CO₃·10H₂O
C. NaCl
D. Ca(OH)₂
41. Which substance is used to remove permanent hardness of water?
A. Baking soda
B. Washing soda
C. Bleaching powder
D. Common salt
42. Baking powder contains baking soda and:
A. hydrochloric acid
B. tartaric acid
C. sulphuric acid
D. nitric acid
43. The gas responsible for making cakes and bread rise is:
A. hydrogen
B. oxygen
C. carbon dioxide
D. nitrogen
44. Bleaching powder is represented in the chapter by:
A. CaCO₃
B. Ca(ClO)₂
C. CaSO₄
D. CaCl₂
45. Bleaching powder can be used to:
A. increase tooth decay
B. disinfect drinking water
C. produce hydrogen chloride
D. soften food
46. Water of crystallisation means:
A. water present on the surface of a salt
B. water chemically associated in a fixed amount with a salt crystal
C. water used to dissolve salt
D. rainwater absorbed by salt
47. The formula of hydrated copper sulphate is:
A. CuSO₄
B. CuSO₄·5H₂O
C. CuSO₄·10H₂O
D. Cu₂SO₄·5H₂O
48. On heating hydrated copper sulphate, its colour changes from:
A. white to blue
B. blue to white
C. yellow to red
D. red to blue
49. Gypsum has the formula:
A. CaSO₄·2H₂O
B. CaSO₄·½H₂O
C. CaCO₃
D. Ca(OH)₂
50. Plaster of Paris is:
A. calcium carbonate
B. calcium sulphate hemihydrate
C. sodium carbonate
D. calcium sulphate dihydrate
SECTION B — MORE MCQs: CONCEPT + APPLICATION
51. A student has four solutions with pH 3, 6, 8 and 12. Which is most acidic?
A. pH 3
B. pH 6
C. pH 8
D. pH 12
52. Which pair contains substances from the same salt family?
A. NaCl and Na₂SO₄
B. NaCl and KCl
C. Both A and B
D. Neither A nor B
53. If an acid is diluted with water, the concentration of H₃O⁺ ions per unit volume:
A. increases
B. decreases
C. becomes zero
D. remains unchanged
54. A solution has pH 6 and another has pH 8. The pH 6 solution is:
A. basic
B. acidic
C. neutral
D. strongly alkaline
55. Which combination gives a neutral salt according to the chapter?
A. Strong acid + strong base
B. Strong acid + weak base
C. Strong base + weak acid
D. Weak acid + weak base only
56. A salt formed from a strong acid and a weak base is expected to be:
A. acidic
B. basic
C. neutral
D. always alkaline
57. A salt formed from a strong base and a weak acid is expected to be:
A. acidic
B. basic
C. neutral
D. always pH 7
58. Which reaction produces a gas that can be identified by a burning test?
A. Acid + metal
B. Acid + base
C. Acid + metal oxide
D. Base + acid
59. Which reaction produces a gas that turns lime water milky?
A. Acid + metal
B. Acid + carbonate
C. Acid + base
D. Base + metal
60. A student wants to test whether a solution is basic using red litmus. The expected observation is:
A. red litmus becomes blue
B. red litmus becomes yellow
C. red litmus becomes pink
D. no possible change
61. Which statement is correct?
A. Every hydrogen-containing compound is an acid.
B. Every base is soluble in water.
C. Acidic properties in aqueous solution are linked to H₃O⁺ formation.
D. Neutral solutions contain no ions at all.
62. Why does adding an acid to water produce heat?
A. The dilution process is exothermic.
B. Water freezes immediately.
C. Hydrogen gas is always produced.
D. Salt crystals are always formed.
63. Which substance is directly associated with tooth decay at low pH?
A. Tooth enamel
B. Sodium chloride
C. Washing soda
D. Bleaching powder
64. Which substance is a mild base used to neutralise excess stomach acid?
A. Milk of magnesia
B. Vinegar
C. Lemon juice
D. Hydrochloric acid
65. A farmer finds that soil is unsuitable because of excessive acidity. Which substances mentioned in the chapter may be used to treat acidic soil?
A. Quick lime/slaked lime/chalk
B. Vinegar
C. HCl
D. Lemon juice
66. Which product of the chlor-alkali process is used in making bleaching powder?
A. Sodium hydroxide
B. Hydrogen
C. Chlorine
D. Sodium chloride
67. Which substance is obtained by heating sodium hydrogencarbonate?
A. Na₂CO₃
B. NaCl
C. CaSO₄
D. HCl
68. Which chemical is used in glass, soap and paper industries?
A. Washing soda
B. Baking soda
C. Hydrogen
D. Hydrochloric acid
69. Which compound is used for making casts for fractured bones?
A. Baking soda
B. Plaster of Paris
C. Washing soda
D. Bleaching powder
70. When Plaster of Paris is mixed with water, it:
A. changes into gypsum
B. changes into baking soda
C. produces chlorine
D. becomes sodium carbonate
SECTION C — FILL IN THE BLANKS
1. Acids turn blue litmus ______.
2. Bases turn red litmus ______.
3. The ion responsible for acidic behaviour in aqueous solution is ______.
4. Bases produce ______ ions in aqueous solution.
5. A base soluble in water is called an ______.
6. The reaction between an acid and a base is called ______.
7. Acid + Base → ______ + ______.
8. Acid + Metal → ______ + ______.
9. Acid + Metal carbonate → ______ + ______ + ______.
10. Carbon dioxide turns lime water ______.
11. The pH of a neutral solution is ______.
12. A solution with pH below 7 is ______.
13. A solution with pH above 7 is ______.
14. Higher hydronium ion concentration means a ______ pH.
15. Acid rain has a pH below ______.
16. Tooth decay begins when mouth pH falls below approximately ______.
17. Common salt has the formula ______.
18. The electrolysis of brine is called the ______ process.
19. Baking soda is chemically called sodium ______.
20. The formula of baking soda is ______.
21. Washing soda is sodium carbonate ______.
22. The formula of washing soda is ______.
23. The gas produced when baking soda reacts with an acid is ______.
24. Bleaching powder is represented in the chapter by the formula ______.
25. Copper sulphate crystals contain ______ water molecules per formula unit.
26. Gypsum has the formula ______.
27. Plaster of Paris is calcium sulphate ______.
28. The formula of Plaster of Paris is ______.
29. The acid present in vinegar is ______ acid.
30. The acid present in curd is ______ acid.
SECTION D — TRUE OR FALSE
Write True or False.
1. Acids turn blue litmus red.
2. Bases produce H₃O⁺ ions as their characteristic ions.
3. All bases are soluble in water.
4. Alkalis are bases that dissolve in water.
5. Acid + metal can produce hydrogen gas.
6. Carbon dioxide turns lime water milky.
7. Neutralisation produces salt and water.
8. Metallic oxides are generally acidic in nature.
9. Non-metallic oxides can show acidic character.
10. Dry HCl gas changes the colour of dry blue litmus.
11. Water is needed for HCl to produce hydronium ions.
12. Acidic solutions can conduct electricity.
13. Glucose solution behaves like hydrochloric acid in the conductivity experiment.
14. pH 7 represents a neutral solution.
15. A lower pH generally means a higher hydronium ion concentration.
16. Acid rain has a pH above 7.
17. Baking soda is sodium hydrogencarbonate.
18. Washing soda is used for removing permanent hardness of water.
19. Baking powder can help cakes rise because CO₂ is produced.
20. Plaster of Paris is gypsum containing more water.
21. Hydrated copper sulphate is blue.
22. Heating hydrated copper sulphate removes its water of crystallisation.
23. Adding water to heated copper sulphate can restore its blue colour.
24. Gypsum contains water of crystallisation.
25. Common salt is sodium chloride.
SECTION E — MATCH THE COLUMNS
Set 1
| Column A | Column B |
|---|---|
| 1. HCl | a. Washing soda |
| 2. NaHCO₃ | b. Common salt |
| 3. NaCl | c. Hydrochloric acid |
| 4. Na₂CO₃·10H₂O | d. Baking soda |
Set 2
| Column A | Column B |
|---|---|
| 1. Vinegar | a. Methanoic acid |
| 2. Curd | b. Acetic acid |
| 3. Ant sting | c. Lactic acid |
| 4. Lemon | d. Citric acid |
Set 3
| Column A | Column B |
|---|---|
| 1. H₃O⁺ | a. Basic character |
| 2. OH⁻ | b. Neutralisation |
| 3. pH 7 | c. Acidic character |
| 4. H⁺ + OH⁻ | d. Neutral |
Set 4
| Column A | Column B |
|---|---|
| 1. CuSO₄·5H₂O | a. Gypsum |
| 2. CaSO₄·2H₂O | b. Plaster of Paris |
| 3. CaSO₄·½H₂O | c. Hydrated copper sulphate |
| 4. Na₂CO₃·10H₂O | d. Washing soda |
Set 5
| Column A | Column B |
|---|---|
| 1. Chlorine | a. Cathode |
| 2. Hydrogen | b. Antacid |
| 3. Magnesium hydroxide | c. Anode |
| 4. Baking soda | d. Fire extinguisher |
SECTION F — VERY SHORT ANSWER QUESTIONS
1. What is an acid-base indicator?
2. Name two natural indicators.
3. Name two synthetic indicators.
4. What are olfactory indicators?
5. Name one olfactory indicator.
6. What is an alkali?
7. What gas is evolved when zinc reacts with dilute sulphuric acid?
8. How can hydrogen gas be tested?
9. What happens when CO₂ is passed through lime water?
10. Name the reaction between an acid and a base.
11. What are the products of neutralisation?
12. Which ion is responsible for acidic properties?
13. Which ion is responsible for basic properties?
14. What is the pH of a neutral solution?
15. What does a pH of 3 indicate?
16. What does a pH of 10 indicate?
17. What is acid rain?
18. What is the approximate pH below which tooth decay begins?
19. Name one substance used as an antacid.
20. Name the acid present in vinegar.
21. Name the acid present in curd.
22. Name the acid associated with an ant sting.
23. What is common salt?
24. What is brine?
25. Name the process used to produce NaOH from brine.
26. Name the three major products of the chlor-alkali process.
27. What is baking soda?
28. Give the chemical formula of baking soda.
29. What is washing soda?
30. Give the chemical formula of washing soda.
31. What is water of crystallisation?
32. What is gypsum?
33. What is Plaster of Paris?
34. Give the formula of Plaster of Paris.
35. State one use of bleaching powder.
SECTION G — SHORT ANSWER QUESTIONS
1. Differentiate between acids and bases using litmus.
2. What is the difference between a base and an alkali?
3. Explain the reaction of zinc with dilute sulphuric acid.
4. Write the general reaction between acids and metals.
5. How can hydrogen gas produced in an acid-metal reaction be identified?
6. Explain the reaction of an acid with a metal carbonate.
7. Why does lime water turn milky when carbon dioxide is passed through it?
8. What happens when excess carbon dioxide is passed through lime water?
9. Define neutralisation and give one equation.
10. Why are metallic oxides called basic oxides?
11. Why are non-metallic oxides considered acidic in nature?
12. Why does an aqueous acid solution conduct electricity?
13. Why do glucose and alcohol solutions not show the same electrical conductivity as acid solutions in the activity?
14. Why does dry HCl gas not show acidic behaviour with dry litmus?
15. Explain the formation of hydronium ions when HCl dissolves in water.
16. What happens to the concentration of H₃O⁺ ions when an acid is diluted?
17. Why should concentrated acid be added slowly to water?
18. Explain the relationship between pH and hydronium ion concentration.
19. Distinguish between strong and weak acids.
20. What is the significance of pH in our digestive system?
21. How does low pH cause tooth decay?
22. Why can baking soda provide relief from a bee sting?
23. What is acid rain and why is it harmful to aquatic organisms?
24. Why is soil pH important for plants?
25. Explain what is meant by a family of salts.
26. How does the acid/base strength affect the pH of a salt solution?
27. Explain the chlor-alkali process.
28. State the uses of the three products formed during the chlor-alkali process.
29. What are the uses of bleaching powder?
30. Why is baking soda useful in baking?
31. Explain two uses of baking soda other than baking.
32. State four uses of washing soda.
33. Explain water of crystallisation using copper sulphate as an example.
34. What happens when gypsum is heated?
35. What happens when Plaster of Paris is mixed with water?
SECTION H — GIVE REASONS
1. Acids turn blue litmus red.
2. Bases turn red litmus blue.
3. An acid solution conducts electricity.
4. Dry HCl gas does not change dry blue litmus.
5. Acid should be added to water and not water to concentrated acid.
6. Antacids are useful during indigestion caused by excess acid.
7. Toothpaste is generally basic.
8. Acid rain can harm aquatic life.
9. Baking soda can be used in antacids.
10. Baking soda is used in baking powder.
11. Washing soda is useful for removing permanent hardness of water.
12. Plaster of Paris should be kept in a moisture-proof container.
13. Copper sulphate crystals turn white when heated.
14. Blue colour returns to heated copper sulphate when water is added.
15. Metallic oxides are called basic oxides.
SECTION I — COMPLETE AND BALANCE THE EQUATIONS
Complete and balance the following.
1. Zn + H₂SO₄ → ______ + ______
2. NaOH + HCl → ______ + ______
3. Na₂CO₃ + HCl → ______ + ______ + ______
4. NaHCO₃ + HCl → ______ + ______ + ______
5. Ca(OH)₂ + CO₂ → ______ + ______
6. CaCO₃ + CO₂ + H₂O → ______
7. CuO + HCl → ______ + ______
8. NaOH + Zn → ______ + ______
9. HCl + H₂O → ______ + ______
10. NaOH → ______ + ______
11. 2NaCl + 2H₂O → ______ + ______ + ______
12. Ca(OH)₂ + Cl₂ → bleaching powder products
13. NaHCO₃ —heat→ ______ + ______ + ______
14. CaSO₄·2H₂O —heat→ ______ + water
15. CaSO₄·½H₂O + water → ______
SECTION J — IDENTIFY THE REACTION TYPE
Identify the type of reaction represented by each equation.
1. HCl + NaOH → NaCl + H₂O
2. Zn + H₂SO₄ → ZnSO₄ + H₂
3. NaHCO₃ + HCl → NaCl + H₂O + CO₂
4. CuO + 2HCl → CuCl₂ + H₂O
5. Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
6. 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
7. CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
SECTION K — OBSERVATION-BASED QUESTIONS
1. A student adds phenolphthalein to sodium hydroxide. What colour should be observed?
2. Hydrochloric acid is gradually added to the above solution. What happens to the colour?
3. Sodium hydroxide is added again after neutralisation. What change is expected?
4. Zinc granules are placed in dilute sulphuric acid. What visible observation is expected?
5. The gas evolved from the zinc-acid reaction is collected and tested with a flame. What observation confirms hydrogen?
6. Sodium carbonate reacts with dilute HCl and the gas is passed through lime water. What happens?
7. Excess CO₂ is then passed through the lime water. What further change occurs?
8. Blue copper sulphate crystals are heated. What happens to their colour?
9. Water is added to the heated copper sulphate. What happens?
10. Plaster of Paris is mixed with water. What happens to the material?
SECTION L — ACTIVITY-BASED QUESTIONS
Activity 1: Indicator Test
A student has three test tubes containing distilled water, an acid and a base. Only red litmus is available.
1. How can the basic solution be identified?
2. How can the acidic solution be distinguished from distilled water after identifying the base?
3. What colour does red litmus show in a basic solution?
Activity 2: Onion as an Olfactory Indicator
Onion strips are exposed separately to acidic and basic solutions.
1. What property of onion is being tested?
2. What are olfactory indicators?
3. Name two other substances mentioned in the chapter that can behave as olfactory indicators.
Activity 3: Acid + Metal
Zinc is treated with dilute sulphuric acid.
1. What gas is released?
2. Why are bubbles seen?
3. Write the balanced equation.
4. How would you confirm the identity of the gas?
Activity 4: Conductivity
A student tests HCl, sulphuric acid, glucose and alcohol solutions using a battery and bulb.
1. Which solutions are expected to make the bulb glow?
2. Why does the bulb glow?
3. What does this experiment tell us about acids in water?
Activity 5: pH Testing
Different household solutions are tested using universal indicator paper.
1. What does the universal indicator tell us?
2. Which solution is more acidic: pH 3 or pH 5?
3. Which has greater OH⁻ concentration: pH 9 or pH 12?
4. Which pH represents neutrality?
SECTION M — CASE-BASED QUESTIONS
Case 1 — Acidity and Antacids
A student overeats and experiences discomfort due to excess stomach acid. A mild basic substance can be used to neutralise the excess acid.
1. What type of medicine is used for such acidity?
2. What is the chemical nature of an antacid?
3. Name the mild base mentioned in the chapter.
4. Write the general reaction responsible for neutralisation.
5. Why should a strong acid not be used to treat excess stomach acid?
Case 2 — Tooth Decay
Bacteria in the mouth can produce acids from sugars and food particles left after eating. When the pH falls sufficiently, tooth enamel can be damaged.
1. Below approximately what pH does tooth decay begin?
2. What produces the acidic conditions?
3. Why can basic toothpaste help?
4. Give one practical way to prevent this problem.
5. Is the harmful environment acidic or basic?
Case 3 — Chlor-Alkali Process
An aqueous solution of sodium chloride is electrolysed. Three useful products are obtained.
1. What is the aqueous sodium chloride solution called?
2. Name the process.
3. Name all three products.
4. At which electrode is chlorine released?
5. At which electrode is hydrogen released?
Case 4 — Baking Soda
A compound used in baking is mixed with an edible weak acid. A gas is produced, making cakes and bread rise.
1. Identify the compound.
2. Give its formula.
3. Name the gas produced.
4. Why does the baked product become soft and spongy?
5. Give two other uses of this compound.
Case 5 — Water of Crystallisation
A student heats blue copper sulphate crystals. They become white. A few drops of water are then added and the blue colour returns.
1. What was removed during heating?
2. What is this water called?
3. Give the formula of hydrated copper sulphate.
4. What happens when water is added again?
5. Does water of crystallisation mean that the crystal is simply wet? Explain.
SECTION N — ASSERTION AND REASON
Choose:
A. Both A and R are true, and R correctly explains A.
B. Both A and R are true, but R does not correctly explain A.
C. A is true, but R is false.
D. A is false, but R is true.
1.
Assertion: Acidic solutions conduct electricity.
Reason: Acids produce ions in aqueous solution.
2.
Assertion: Dry HCl gas does not show acidic behaviour with dry litmus.
Reason: Water is needed for the formation of hydronium ions.
3.
Assertion: A solution with pH 2 is more acidic than one with pH 5.
Reason: Lower pH corresponds to higher hydronium ion concentration.
4.
Assertion: All bases are alkalis.
Reason: Alkalis are bases soluble in water.
5.
Assertion: Baking soda is useful as an antacid.
Reason: Baking soda is a mild basic salt.
6.
Assertion: Washing soda is useful for removing permanent hardness of water.
Reason: Washing soda is sodium carbonate decahydrate.
7.
Assertion: Toothpaste can help prevent tooth decay.
Reason: Toothpaste is generally basic and can neutralise excess acid.
8.
Assertion: Acid rain can affect aquatic organisms.
Reason: Acid rain can lower the pH of water bodies.
9.
Assertion: Heating hydrated copper sulphate changes its colour.
Reason: Water of crystallisation is removed during heating.
10.
Assertion: Plaster of Paris is stored in moisture-proof containers.
Reason: It can react with moisture and convert back into gypsum.
11.
Assertion: CO₂ turns lime water milky.
Reason: Calcium carbonate is formed.
12.
Assertion: A strong acid produces more H⁺ ions than a weak acid of the same concentration.
Reason: Strong acids ionise to a greater extent.
SECTION O — APPLICATION-BASED QUESTIONS
1. A student finds that a liquid turns blue litmus red and has pH 3. What can you conclude?
2. A solution has pH 11. Predict its effect on red litmus.
3. A farmer finds that his field soil is too acidic. Which substances from the chapter could be considered for treatment?
4. A person has excessive stomach acidity. Explain chemically why a mild base can provide relief.
5. A student accidentally adds water quickly to concentrated acid. Why can this be dangerous?
6. Why would an acid react with marble/chalk and release bubbles?
7. A gas turns lime water milky. What can you infer?
8. A student heats baking soda and notices gas evolution. Which gas is expected?
9. Why is washing soda useful in households?
10. Why would a plaster cast harden after water is added to Plaster of Paris?
11. Why does the same salt family concept apply to NaCl and Na₂SO₄?
12. A solution changes red litmus to blue. Would you expect its pH to be above or below 7? Explain.
SECTION P — COMPETENCY-BASED QUESTIONS
1. Four solutions have pH values 2, 6, 7 and 12.
Answer:
a. Which is most acidic?
b. Which is neutral?
c. Which is most alkaline?
d. Arrange them from acidic to basic.
2. Solution A has pH 4 and solution B has pH 8.
a. Which has greater H₃O⁺ concentration?
b. Which is acidic?
c. Which is basic?
d. What happens to H₃O⁺ concentration when an acid is diluted?
3. A student is given NaCl, NaHCO₃ and Na₂CO₃·10H₂O.
a. Identify the common salt.
b. Identify baking soda.
c. Identify washing soda.
d. Which one is used for removing permanent hardness?
4. A student has CuSO₄·5H₂O and CaSO₄·2H₂O.
a. Identify each compound.
b. Which one is associated with gypsum?
c. Which one is blue?
d. What is meant by the water in these formulae?
5. A chemical reaction produces salt, water and carbon dioxide.
a. Which type of reactants could produce these products?
b. Give one example.
c. How could the CO₂ be tested?
SECTION Q — LOGICAL / NUMERICAL-TYPE QUESTIONS
1. A solution has pH 4 while another has pH 7. Which has the greater hydronium ion concentration?
2. Five solutions have pH values:
A = 4
B = 1
C = 11
D = 7
E = 9
Identify:
a. Neutral solution
b. Strongly acidic solution
c. Strongly alkaline solution
d. Weakly acidic solution
e. Weakly alkaline solution
3. Arrange the following in increasing order of hydrogen-ion concentration:
pH 9, pH 4, pH 7, pH 1, pH 11.
4. A solution’s pH changes from 3 to 6 after dilution. Has its hydronium ion concentration increased or decreased?
5. Two acids have the same concentration. Acid X produces more H⁺ ions than Acid Y. Which is stronger? Explain.
6. Equal amounts of magnesium react separately with hydrochloric acid and acetic acid of the same concentration. Which reaction is expected to show more vigorous fizzing, and why?
7. A neutralisation experiment requires 8 mL of HCl solution to neutralise 10 mL of NaOH solution. Assuming the same concentrations and reaction conditions, what volume of the same HCl solution would be needed for 20 mL of the NaOH solution?
SECTION R — HOTS QUESTIONS
1. A compound contains hydrogen, but its aqueous solution does not show acidic behaviour. Does this contradict the definition of an acid? Explain.
2. A student says, “A solution with pH 6 is neutral because 6 is close to 7.” Is the statement correct? Explain.
3. Two solutions have equal concentration. One is HCl and the other is acetic acid. Explain why their acidic strength may differ.
4. Why is the presence of H⁺ alone not enough to explain the behaviour of acids in water? What form does hydrogen ion take in water?
5. If a solution has OH⁻ ions, can it still contain H⁺ ions? Explain why the solution may nevertheless be basic.
6. Why does dilution reduce the concentration of H₃O⁺ ions without necessarily removing all acidic character?
7. Why does excess CO₂ make the milkiness of lime water disappear?
8. A student says that water of crystallisation is simply moisture trapped inside salt crystals. Explain why this is an incomplete explanation.
9. Why is sodium hydrogencarbonate called a basic salt even though it is a salt rather than a base?
10. Explain why a salt need not always have a neutral pH.
11. Why can a non-metallic oxide behave similarly to an acid when reacting with a base?
12. A solution changes from pH 5 to pH 8. Has it become more acidic or more basic? Explain using ion concentration.
SECTION S — LONG ANSWER QUESTIONS
1. Explain the chemical properties of acids under the following headings:
a. Reaction with metals
b. Reaction with metal carbonates
c. Reaction with metal hydrogencarbonates
d. Reaction with bases
e. Reaction with metallic oxides
Give suitable balanced equations.
2. Explain why acids show acidic character only in aqueous solution. Include the role of H₃O⁺ ions and electrical conductivity.
3. Explain the pH scale and discuss its importance in:
a. digestion
b. tooth decay
c. acid rain
d. soil
e. animal/plant defence
4. Explain the chlor-alkali process with:
a. definition of brine
b. chemical equation
c. three products
d. electrode at which chlorine is produced
e. electrode at which hydrogen is produced
f. formation/use of sodium hydroxide
5. Describe baking soda in detail, including:
a. chemical name
b. formula
c. preparation
d. reaction on heating
e. use in baking
f. use as an antacid
g. use in fire extinguishers
6. Explain washing soda under the following headings:
a. formula
b. relation with sodium carbonate
c. basic nature
d. industrial uses
e. domestic use
f. role in removing permanent hardness
7. Explain water of crystallisation with the help of copper sulphate and gypsum.
8. Explain the preparation, formula, reaction with water and uses of Plaster of Paris.
9. Explain the relationship among acids, bases and salts through neutralisation reactions.
10. Describe how indicators can be used to distinguish acids and bases. Include natural, synthetic and olfactory indicators.
SECTION T — MIXED REVISION QUESTIONS
1. Define acid.
2. Define base.
3. Define alkali.
4. Define indicator.
5. Define neutralisation.
6. Define pH.
7. Define acid rain.
8. Define water of crystallisation.
9. Define strong acid.
10. Define weak acid.
11. What is brine?
12. What is the chlor-alkali process?
13. What is baking soda?
14. What is washing soda?
15. What is Plaster of Paris?
16. Why does an acid react with zinc to produce hydrogen?
17. Why does an acid react with sodium carbonate to produce CO₂?
18. Why is neutralisation useful in everyday life?
19. Why does pH matter in agriculture?
20. Why is pH important in the mouth?
21. Why is pH important in the stomach?
22. Why is baking soda considered mildly basic?
23. Why is washing soda considered a basic salt?
24. Why does hydrated copper sulphate lose its blue colour on heating?
25. Why does the blue colour return when water is added?
SECTION U — EXAM-STYLE INTEGRATED QUESTIONS
Question 1 — 5 Marks
a. What happens when zinc reacts with dilute sulphuric acid?
b. Write the balanced equation.
c. Name the gas evolved.
d. Give one test for this gas.
e. State the general reaction of an acid with a metal.
Question 2 — 5 Marks
a. Define neutralisation.
b. Give one chemical equation.
c. What happens to H⁺ and OH⁻ ions during neutralisation?
d. Name one everyday application of neutralisation.
e. Why is an antacid useful during indigestion?
Question 3 — 5 Marks
A solution has pH 3.
a. Is it acidic or basic?
b. Is its H₃O⁺ concentration relatively high or low?
c. What would happen to its pH after dilution?
d. What happens to H₃O⁺ concentration on dilution?
e. Name an instrument/material used to estimate pH.
Question 4 — 5 Marks
a. What is common salt?
b. What is brine?
c. Name the process in which brine is electrolysed.
d. Write its chemical equation.
e. Name the three products.
Question 5 — 5 Marks
a. Give the chemical formula of baking soda.
b. What happens when it is heated?
c. Name the gas produced.
d. Explain its role in baking powder.
e. Give one medicinal use.
Question 6 — 5 Marks
a. What is water of crystallisation?
b. Give the formula of hydrated copper sulphate.
c. What happens when it is heated?
d. How can its original colour be restored?
e. Give the formula of gypsum.
SECTION V — ANSWER KEY
MCQs 1–25
1-C
2-D
3-B
4-C
5-B
6-C
7-C
8-B
9-C
10-B
11-B
12-C
13-C
14-B
15-C
16-C
17-B
18-C
19-B
20-C
21-A
22-C
23-B
24-A
25-C
MCQs 26–50
26-B
27-C
28-B
29-A
30-C
31-B
32-C
33-B
34-B
35-B
36-A
37-B
38-B
39-B
40-B
41-B
42-B
43-C
44-B
45-B
46-B
47-B
48-B
49-A
50-B
MCQs 51–70
51-A
52-C
53-B
54-B
55-A
56-A
57-B
58-A
59-B
60-A
61-C
62-A
63-A
64-A
65-A
66-C
67-A
68-A
69-B
70-A
FILL IN THE BLANKS — ANSWERS
- red
- blue
- H₃O⁺ / H⁺(aq)
- OH⁻
- alkali
- neutralisation
- salt, water
- salt, hydrogen
- salt, carbon dioxide, water
- milky
- 7
- acidic
- basic/alkaline
- lower
- 5.6
- 5.5
- NaCl
- chlor-alkali
- hydrogencarbonate
- NaHCO₃
- decahydrate
- Na₂CO₃·10H₂O
- carbon dioxide
- Ca(ClO)₂
- five
- CaSO₄·2H₂O
- hemihydrate
- CaSO₄·½H₂O
- acetic
- lactic
TRUE/FALSE — ANSWERS
- True
- False
- False
- True
- True
- True
- True
- False
- True
- False
- True
- True
- False
- True
- True
- False
- True
- True
- True
- False
- True
- True
- True
- True
- True
MATCH THE COLUMNS — ANSWERS
Set 1
1-c, 2-d, 3-b, 4-a
Set 2
1-b, 2-c, 3-a, 4-d
Set 3
1-c, 2-a, 3-d, 4-b
Set 4
1-c, 2-a, 3-b, 4-d
Set 5
1-c, 2-a, 3-b, 4-d
ASSERTION–REASON — ANSWERS
1-A
2-A
3-A
4-D
5-A
6-B
7-A
8-A
9-A
10-A
11-A
12-A
NUMERICAL / LOGICAL ANSWERS
1. pH 4 solution has greater H₃O⁺ concentration.
2.
- Neutral → D (7)
- Strongly acidic → B (1)
- Strongly alkaline → C (11)
- Weakly acidic → A (4)
- Weakly alkaline → E (9)
3. Increasing H⁺ concentration:
pH 11 < pH 9 < pH 7 < pH 4 < pH 1
4. H₃O⁺ concentration decreases.
5. Acid X is stronger because it produces more H⁺ ions at the same concentration.
6. Hydrochloric acid is expected to react more vigorously because it produces more H⁺ ions than acetic acid under the stated comparison.
7. 16 mL of HCl solution.
MUST-PRACTISE EQUATIONS
For board preparation, students should be able to write and balance these without looking:
- Zn + H₂SO₄ → ZnSO₄ + H₂
- NaOH + HCl → NaCl + H₂O
- Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
- NaHCO₃ + HCl → NaCl + H₂O + CO₂
- Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
- CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
- CuO + 2HCl → CuCl₂ + H₂O
- 2NaOH + Zn → Na₂ZnO₂ + H₂
- HCl + H₂O → H₃O⁺ + Cl⁻
- NaOH → Na⁺ + OH⁻
- 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
- 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
- CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
- CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
FINAL REVISION CHECKLIST
Before considering this chapter fully prepared, a Class 10 student should be able to:
☐ Identify acids and bases using indicators
☐ Explain olfactory indicators
☐ Write acid + metal reactions
☐ Identify and test hydrogen gas
☐ Write acid + carbonate reactions
☐ Explain the lime-water test for CO₂
☐ Explain neutralisation
☐ Explain basic and acidic oxides
☐ Explain H₃O⁺ formation
☐ Explain why dry HCl is not acidic
☐ Explain electrical conductivity of acids/bases
☐ Read and compare pH values
☐ Distinguish strong and weak acids/bases
☐ Explain pH in digestion
☐ Explain tooth decay and pH
☐ Explain acid rain
☐ Explain soil pH
☐ Identify naturally occurring acids
☐ Explain salt families
☐ Predict whether certain salts are acidic/basic/neutral
☐ Explain the chlor-alkali process
☐ Recall uses of bleaching powder
☐ Explain baking soda and its uses
☐ Explain washing soda and its uses
☐ Define water of crystallisation
☐ Explain hydrated copper sulphate
☐ Explain gypsum and Plaster of Paris
☐ Write all important balanced equations
☐ Solve pH-based reasoning questions
☐ Answer application and case-based questions