NCERT Solutions for Class 10 Science Chapter 2: Acids, Bases and Salts – Exercise Questions and Answers

CH-2 Acids , Bases and Salts

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Introduction

NCERT Solutions for Class 10 Science Chapter 2 – Acids, Bases and Salts (Exercise Questions and Answers) provide clear, accurate, and step-by-step explanations for all the questions given in the NCERT textbook. These solutions help students understand important concepts such as the properties of acids and bases, the pH scale, chemical reactions involving acids and bases, salts, indicators, washing soda, baking soda, and plaster of Paris.

Prepared according to the latest CBSE syllabus, these answers are written in simple language to make learning easier and more effective. By practicing these NCERT exercise questions and answers, students can strengthen their conceptual understanding, improve problem-solving skills, and prepare confidently for school examinations as well as board exams.

This comprehensive guide serves as a valuable study resource for quick revision and better understanding of Chapter 2 – Acids, Bases and Salts.

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CH-2 Acids , Bases and Salts

EXERCISE SOLUTION

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Ques 1:- A solution turns red litmus blue, its pH is likely to be

(a) 1      (b) 4      (c) 5      (d) 10

Ans:- (d) The solution which turns red litmus blue is basic. Hence, its pH should be greater than 7.

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Ques 2:- A solution reacts with crushed egg shells to give a gas that turns lime water milky. The solution contains

(a) NaCl           (b) HCl      (c) LiCl      (d) KCl

Ans:- (b) HCl

• The egg-shells are made of calcium carbonate and the gas which turns lime- water milky is carbon dioxide.

• Carbon dioxide gas can be formed by action of an acid solution on calcium carbonate (or egg-shells). So, the solution contains HCl.

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Ques 3:- 10 mL of solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be

(a) 4 mL           (b) 8 mL      (c) 12 mL      (d) 16 mL

Ans:- (d) 16 ml - In this case the amount of the same HCl solution required to neutralize. it is also double,

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Ques 4:- Which one or the following types, of medicines is used Tor treating.

(a) Antibiotic           (b) Analgesic      (c) Antacid      (d) Antiseptic.

Ans:- (c) Antacid.

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Ques 5:- Write word equations and then balanced equations for the reactions taking place when

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Ques (a):- Dilute sulphuric acid reacts with zinc granules.

Ans:-

Sulphuric acid (aq) + Zinc (s) → Zinc sulphate (aq) + Hydrogen (g)

H₂SO₄(aq) + Zn(s) → ZnSO₄(aq) + H₂(g)

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Ques (b):- dilute hydrochloric acid reacts with magnesium ribbon.

Ans:-

Hydrochloric acid (aq) + Magnesium (s) → Magnesium chloride(aq) + Hydrogen (g)

2HCl(aq) + Mg(s) → MgCl₂(aq) + H₂(g)

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Ques (c):- dilute sulphuric acid reacts with aluminium powder.

Ans:-

Sulphuric acid (aq) +Aluminium (s) → Aluminium sulphate (aq) + Hydrogen (g)

2HCl(aq) + 2Al(s) → Al₂ (SO₄)₃(aq) + H₂(g)

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Ques (d):- dilute hydrochloric acid reacts with cross fillings.

Ans:-

(d) Hydrochloric acid (aq) + Iron (s) → Iron chloride (aq) + Hydrogen (g)

2HCl(aq) + Fe (s) → FeCl₂ (aq) + H₂(g)

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Ques 6:- Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.

The following activity can be carried out to prove it.

Activity :- Materials Required :- Beaker, rubber cork, nail, 6 V battery, connecting wires, bulb, switch, ethyl alcohol.

Procedure :- :- Set Up the apparatus

• Take ethyl alcohol in the beaker such that the upper ends of the nail remain 2 cm above the level of alcohol.

• When the switch is turned on, we observe that the bulb does not glow.

• Repeat the experiment by taking glucose solution in place of alcohol. Again, we observe that the bulb does not glow.

• This shows that the flow of current does not take place in both the cases. This proves that there are no H+ ions in alcohol and glucose solution. as electricity is conducted through the ions (H+ ions) in solution.

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Ques 7:- Why does distilled water not conduct electricity, whereas rain water does?

Ans:-

• Rain water contains dissolved gases and salts. Due to the presence of ions (including H⁺ ions formed from dissolved acidic gases), it can conduct electricity.

• Distilled water is pure water and contains almost no dissolved salts or ions.

• Since electricity is conducted through the movement of ions, distilled water does not conduct electricity, whereas rain water does.

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Ques 8:- Why do acids not show acidic behaviour in the absence of water?

Ans:-

• Acids produce H⁺ ions only in the presence of water.

• These H⁺ ions combine with water molecules to form hydronium ions (H₃O⁺), which are responsible for the acidic behaviour of acids.

For example:

HCl + H₂O → H₃O⁺ + Cl⁻

• In the absence of water, hydronium ions are not formed. Therefore, acids do not show acidic behaviour in the absence of water.

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Ques 9:- Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively.

Which solution is:

(a) Neutral?    (b) Strongly alkaline?    (c) Strongly acidic?

(d) Weakly acidic?    (e) Weakly alkaline?

Arrange the pH in increasing order of hydrogen ion concentration.

Ans:-

(a) The solution D having pH 7 is neutral.

(b) The solution C having pH 11 is strongly alkaline.

(c) The solution B having pH 1 is strongly acidic.

(d) The solution A having pH 4 is weakly acidic.

(e) The solution E having pH 9 is weakly alkaline.

Increasing order of hydrogen ion (H⁺) concentration:

C < E < D < A < B

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Ques 10:- Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and Why ?

Ans:-

HCl is a stronger acid than CH₃COOH. Therefore, the concentration of H⁺ ions in test tube A is greater than in test tube B. Magnesium reacts faster with hydrochloric acid, producing hydrogen gas at a higher rate.

Hence, fizzing will occur more vigorously in test tube A because hydrogen gas is evolved more rapidly.

Reaction:

Mg + 2HCl → MgCl₂ + H₂↑

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Ques 11:- Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your answer.

Ans:-

When milk turns into curd, bacteria convert lactose (milk sugar) into lactic acid. The formation of lactic acid increases the acidity of the curd. Therefore, the pH decreases from 6 to a lower value (less than 6) as milk changes into curd.

This happens because acids have lower pH values than neutral substances.

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Ques 12:- A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the milk from 6 to slightly alkaline?

Ans:- (a)

• A milkman adds a small amount of baking soda (sodium hydrogen carbonate) to fresh milk because it is basic in nature. This makes the milk slightly alkaline and increases its pH from 6 to a value above 7.

• As a result, more lactic acid must be produced before the milk becomes acidic, which delays souring and curdling of the milk.

This is why the pH of the milk is shifted from 6 to slightly alkaline.

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(b) Why does this milk take a long time to set as curd?

Ans:- (b)

• During the formation of curd, bacteria produce lactic acid. The sodium hydrogen carbonate (baking soda) added to the milk neutralizes this lactic acid.

• Therefore, more lactic acid has to be produced before the milk becomes sufficiently acidic to set into curd. Hence, the milk takes a longer time to set as curd.

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Ques 13:- Plaster of Paris should be stored in a moisture proof container. Explain why?

Ans:-

Plaster of Paris (POP) reacts with moisture present in the air to form gypsum. As a result, it hardens and loses its ability to be moulded into different shapes.

Therefore, Plaster of Paris should be stored in a moisture-proof container to prevent it from absorbing moisture and setting into a hard mass.

Reaction:

CaSO₄·½H₂O + 3/2 H₂O → CaSO₄·2H₂O

Plaster of Paris :- CaSO₄·½H₂O
Chemical name:- Calcium sulphate hemihydrate

Gypsum :- CaSO₄·2H₂O
Chemical name:- Calcium sulphate dihydrate

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Ques 14:- What is a neutralisation? Give two examples.

Ans:- The reaction between an acid and a base to form salt and water is called a neutralisation reaction.

Examples:

1. NaOH + HCl → NaCl + H₂O

2. KOH + HNO₃ → KNO₃ + H₂O

Neutralisation can also be represented by the ionic equation:

H⁺ (aq) + OH⁻(aq) → H₂O(l)

Here, the H⁺ ions from the acid combine with the OH⁻ ions from the base to form water.

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Ques 15:- Give two important uses of washing soda and baking soda.

Ans:-

Uses of Washing Soda (Na₂CO₃·10H₂O):

(i) It is used as a cleansing agent for domestic purposes and for removing the permanent hardness of water.

(ii) It is used in the manufacture of glass, soap and paper.

Uses of Baking Soda (NaHCO₃):

(i) It is used for making baking powder, which is a mixture of sodium hydrogen carbonate and a mild edible acid such as tartaric acid.

(ii) It is used as an ingredient in antacids to neutralise excess acid in the stomach.

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Conclusion

The NCERT Solutions for Class 10 Science Chapter 2 – Acids, Bases and Salts (Exercise Questions and Answers) help students develop a strong understanding of important concepts related to acids, bases, salts, pH, indicators, and their everyday applications. These well-explained solutions make learning easier and assist students in solving textbook questions with confidence.

Regular practice of these exercise questions improves conceptual clarity, strengthens exam preparation, and helps students achieve better academic performance. Students can use these solutions for quick revision and effective preparation for school and board examinations.

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Frequently Asked Questions (FAQs)

Q1. Why are NCERT Solutions for Class 10 Science Chapter 2 important?

These solutions help students understand the concepts of acids, bases, salts, pH, indicators, and their applications in a simple and systematic manner.

Q2. What topics are covered in Chapter 2 – Acids, Bases and Salts?

The chapter covers acids, bases, indicators, pH scale, neutralisation reactions, salts, washing soda, baking soda, and plaster of Paris.

Q3. Are these NCERT solutions useful for CBSE board exam preparation?

Yes, these solutions are based on the latest CBSE syllabus and help students prepare effectively for school tests and board examinations.

Q4. What is the importance of the pH scale in Chapter 2?

The pH scale helps determine whether a substance is acidic, basic, or neutral and indicates its strength.

Q5. Can these solutions be used for quick revision before exams?

Yes, the step-by-step answers and concise explanations make these solutions an excellent resource for quick revision and last-minute exam preparation.

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