Class 10 Science – Chapter 2: Acids, Bases and Salts
Intext and Exercise Questions with Answers from NCERT Book
Intext Questions and Answers
Page 18
1. Q1: You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Dip the red litmus paper in each test tube:
- In acid: Red litmus remains red.
- In base: Red litmus turns blue.
- In distilled water: Red litmus does not change (neutral).
Page 22
2. Q1: Why should curd and sour substances not be kept in brass and copper vessels?
Because they contain acids which react with the metals to form toxic compounds.
3. Q2: Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Hydrogen gas is liberated.
Example: Zn + H2SO4 → ZnSO4 + H2↑
Test: Burning matchstick gives pop sound.
4. Q3: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation and name the type of reaction.
A = CaCO₃
Reaction: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
Type: Acid-carbonate reaction.
Page 25
5. Q1: Why do HCl, HNO₃ show acidic character in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Because they release H⁺ ions in water; alcohol and glucose do not.
6. Q2: Why does an aqueous solution of an acid conduct electricity?
Due to free H⁺ ions which conduct current.
7. Q3: Why does dry HCl gas not change the colour of the dry litmus paper?
Dry HCl has no H⁺ ions as it lacks water.
8. Q4: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
To prevent violent exothermic reactions and splashing.
9. Q5: How is the concentration of H₃O⁺ ions affected when the solution of an acid is diluted?
It decreases, making the solution less acidic.
10. Q6: How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide?
It increases, making the solution more basic.
Exercise Questions and Answers
11. Q1: A solution turns red litmus blue, its pH is likely to be –
Answer: (d) 10
12. Q2: A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains –
Answer: (b) HCl
13. Q3: 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given HCl solution. If we take 20 mL of the same NaOH solution, the amount of HCl solution required to neutralise it will be –
Answer: (d) 16 mL
14. Q4: Which one of the following types of medicines is used for treating indigestion?
Answer: (c) Antacid
15. Q5: Write word equations and then balanced equations for the reactions taking place when –
(a) Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
Balanced: H₂SO₄ + Zn → ZnSO₄ + H₂↑
(b) Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
Balanced: 2HCl + Mg → MgCl₂ + H₂↑
(c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
Balanced: 3H₂SO₄ + 2Al → Al₂(SO₄)₃ + 3H₂↑
(d) Hydrochloric acid + Iron → Iron chloride + Hydrogen
Balanced: 6HCl + 2Fe → 2FeCl₃ + 3H₂↑
16. Q6: Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.
Set up an apparatus with a bulb, battery, wires and electrodes in a solution of glucose or alcohol. Bulb does not glow → no free H⁺ ions → no conductivity.
17. Q7: Why does distilled water not conduct electricity, whereas rain water does?
Distilled water lacks ions; rainwater has dissolved CO₂ → forms acids → releases ions → conducts.
18. Q8: Why do acids not show acidic behaviour in the absence of water?
Because acids need to ionise (release H⁺ ions), and ionisation occurs only in water.
19. Q9: Five solutions A, B, C, D and E have pH values of 0, 3, 5, 8 and 14 respectively. Which solution is:
(a) Most acidic: A
(b) Strongly alkaline: E
(c) Weakly acidic: C
(d) Weakly alkaline: D
(e) Neutral: None
20. Q10: Equal lengths of magnesium ribbon are taken in test tubes A and B. HCl is added to A, and acetic acid to B. Which one will react more vigorously and why?
Test tube A (with HCl) reacts more vigorously because HCl is a strong acid and ionises more than acetic acid.
21. Q11: Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain.
pH will decrease due to formation of lactic acid (curd is more acidic).
22. Q12: A milkman adds a very small amount of baking soda to fresh milk.
(a) To prevent curdling by shifting pH slightly to basic.
(b) Milk takes longer to set as curd due to neutralisation of lactic acid.
23. Q13: Plaster of Paris should be stored in a moisture-proof container. Explain why?
Plaster of Paris absorbs moisture and becomes hard gypsum, making it unusable.
24. Q14: What is a neutralization reaction? Give two examples.
Reaction of acid with base to form salt and water.
Examples:
NaOH + HCl → NaCl + H₂O
NH₄OH + HNO₃ → NH₄NO₃ + H₂O
25. Q15: Give two important uses of washing soda and baking soda.
Washing soda: softening water, glass/soap industry
Baking soda: baking agent, used in fire extinguishers
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