TOPIC 8 OF 50

Acids, Bases and Salts – NCERT Exercises

Q: How do I solve NCERT Class 10 Science Chapter 2 (Acids, Bases and Salts) exercise questions for the CBSE board exam?

Solve NCERT Chapter 2 u2014 Acids, Bases and Salts u2014 exercise questions by first reading the question carefully, writing down the given data, recalling the relevant concepts like acids, bases, pH, and applying them step by step. This Part 4 covers every intext and end-of-chapter exercise from the NCERT textbook. Write balanced equations, label diagrams clearly and show each step u2014 CBSE Class 10 board examiners award step marks even if the final answer has a small slip. Practising these solutions strengthens conceptual clarity and builds speed for the board exam.

Q: How many marks does Chapter 2 u2014 Acids, Bases and Salts u2014 carry in the Class 10 Science CBSE paper?

Chapter 2 u2014 Acids, Bases and Salts u2014 is part of the Class 10 Science syllabus and typically contributes 5u20139 marks in the CBSE board paper, depending on the annual weightage. Questions are drawn from definitions, reasoning, numerical/descriptive problems and diagrams on topics like acids, bases, pH. Solving the NCERT exercises in this part is essential because CBSE directly references NCERT for question design.

🎓 Class 10 Science CBSE Theory Ch 2 — Acids, Bases and Salts ⏱ ~21 min

🌐 Language: [gtranslate]

🧠 AI-Powered MCQ Assessment ▲

This MCQ module is based on: Acids, Bases and Salts – NCERT Exercises

No. of Questions:

Difficulty Level:

Myaischool Lt Science Assessment ▲

[myaischool_lt_science_assessment grade_level="class_10" science_domain="chemistry" difficulty="intermediate"]

Chapter Summary

Acids are substances that produce H⁺(aq) ions when dissolved in water. Bases produce OH^-(aq) ions.
Indicators such as litmus, turmeric, methyl orange and phenolphthalein help identify acids and bases.
Acids react with metals to give a salt and hydrogen gas. Certain metals (Zn, Al) also react with bases to give hydrogen.
An acid reacts with a base to form salt and water — this is called neutralisation.
Metal carbonates and bicarbonates react with acids to give salt, water and CO₂.
Acids in water release H⁺ (or H₃O⁺), which is responsible for their acidic character. Water is essential for acids to show acidic behaviour.
The pH scale (0-14) measures the strength of acids and bases. pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic.
pH is important in everyday life: digestive system, tooth decay, soil treatment, self-defence by animals, factory effluent treatment.
While diluting acids, always add acid to water (never water to acid) as the process is highly exothermic.
Common salt (NaCl) is the raw material for NaOH, bleaching powder, baking soda, and washing soda.
The chlor-alkali process electrolyses brine to produce NaOH, Cl₂, and H₂.
Baking soda (NaHCO₃) is used in cooking, as an antacid, and in fire extinguishers.
Washing soda (Na₂CO₃·10H₂O) is used for cleaning, softening hard water, and in glass/soap manufacturing.
Bleaching powder (CaOCl₂) is used for water purification and textile bleaching.
Plaster of Paris (CaSO₄·½H₂O) is made by heating gypsum; it sets hard when mixed with water.
Water of crystallisation is a fixed number of water molecules in the crystal structure of a salt (e.g., CuSO₄·5H₂O).

Key Terms

AcidProduces H⁺(aq) ions in water; turns blue litmus red

BaseProduces OH^-(aq) ions in water; turns red litmus blue

AlkaliA base that is soluble in water (e.g., NaOH, KOH)

IndicatorSubstance that changes colour/odour in acid or base

NeutralisationAcid + Base → Salt + Water (exothermic)

pH ScaleScale from 0-14 measuring hydrogen ion concentration

Hydronium IonH₃O⁺ — formed when H⁺ combines with H₂O

Chlor-Alkali ProcessElectrolysis of brine → NaOH + Cl₂ + H₂

Baking SodaNaHCO₃ — cooking, antacid, fire extinguisher

Washing SodaNa₂CO₃·10H₂O — cleaning, water softening

Bleaching PowderCaOCl₂ — water purification, textile bleaching

Plaster of ParisCaSO₄·½H₂O — casts, moulds, decoration

Water of CrystallisationFixed water molecules in crystal structure of a salt

GypsumCaSO₄·2H₂O — raw material for Plaster of Paris

NCERT Textbook Exercises

Q1. A solution turns red litmus blue. What is its pH likely to be — 5, 7, or 12?

Answer: pH = 12. A solution that turns red litmus blue is basic in nature. Among the given options, only pH 12 is above 7 (basic). pH 5 would be acidic (turns blue litmus red) and pH 7 would be neutral (no colour change).

Q2. A solution reacts with crushed egg shells to give a gas that turns lime water milky. The solution contains:

Answer: The solution contains an acid. Egg shells are made of calcium carbonate (CaCO₃). When an acid reacts with CaCO₃, it produces CO₂ gas, which turns lime water milky.
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
The gas (CO₂) turns lime water milky: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O.

Q3. Ten mL of NaOH solution is found to be completely neutralised by 8 mL of a given HCl solution. If we take 20 mL of the same NaOH solution, what volume of HCl would be needed to neutralise it?

Answer: 16 mL of HCl. Since 10 mL NaOH requires 8 mL HCl, the ratio is 10:8 or 5:4. For 20 mL NaOH (which is double), we need double the HCl = 2 × 8 = 16 mL of the same HCl solution.

Q4. For the reaction of sodium hydroxide with hydrochloric acid, write: (i) the word equation, and (ii) the balanced chemical equation with state symbols.

Answer:
(i) Word equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
(ii) Balanced equation:

\(\text{NaOH}(aq) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l)\)

This is a neutralisation reaction (acid + base → salt + water).

Q5. How is the concentration of H₃O⁺ ions affected when a solution of an acid is diluted?

Answer: When an acid solution is diluted (by adding water), the concentration of H₃O⁺ (hydronium) ions per unit volume decreases. The total number of H₃O⁺ ions remains the same, but they are now spread over a larger volume of solution. As a result, the pH of the solution increases (moves closer to 7), meaning the solution becomes less acidic.

Q6. Why should curd and sour substances not be kept in brass and copper vessels?

Answer: Curd and sour substances contain acids (lactic acid in curd, citric acid in lemon, etc.). These acids react with the metals — brass (alloy of copper and zinc) and copper — to form toxic metallic salts. For example, copper reacts with acids to form copper compounds that are poisonous and harmful to health. This is why such food items should always be stored in glass or stainless steel vessels.

Q7. Which type of medicines are used for treating indigestion caused by acidity? How do they work?

Answer: Antacids (anti-acid medicines) are used to treat indigestion caused by excess acid in the stomach. Common antacids include milk of magnesia — Mg(OH)₂, and baking soda — NaHCO₃. They work by neutralising the excess hydrochloric acid (HCl) produced in the stomach. Being mild bases, they react with the acid to form salt and water, thereby reducing the acidity and providing relief from pain and discomfort.

Q8. Why do acids not show acidic behaviour in the absence of water?

Answer: Acids show their characteristic acidic behaviour (sour taste, colour change of indicators, reaction with metals, etc.) only because they produce H⁺(aq) ions when dissolved in water. Without water, the acid molecules cannot dissociate into ions — they remain as undissociated molecules. Since it is the H⁺(aq) ion that is responsible for all acidic properties, acids cannot show acidic behaviour in the absence of water. For example, dry HCl gas does not change the colour of dry litmus paper, but when moisture is present, it turns blue litmus red.

Q9. Five solutions A, B, C, D and E, when tested with universal indicator, showed pH values of 4, 1, 11, 7 and 9 respectively. Which solution is: (a) neutral? (b) strongly alkaline? (c) strongly acidic? (d) weakly acidic? (e) weakly alkaline?

Answer:

Solution	pH	Nature
A	4	(d) Weakly acidic
B	1	(c) Strongly acidic
C	11	(b) Strongly alkaline
D	7	(a) Neutral
E	9	(e) Weakly alkaline

pH 7 = neutral; pH far below 7 = strongly acidic; pH slightly below 7 = weakly acidic; pH far above 7 = strongly alkaline; pH slightly above 7 = weakly alkaline.

Q10. Equal lengths of magnesium ribbons are taken in two 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?

Answer: Fizzing will occur more vigorously in test tube A (containing HCl). This is because HCl is a strong acid — it dissociates completely in water, producing a higher concentration of H⁺ ions. Acetic acid is a weak acid — it only partially dissociates, producing fewer H⁺ ions. Since the rate of reaction with magnesium depends on the concentration of H⁺ ions, the reaction is faster and more vigorous with HCl. Both reactions produce hydrogen gas (fizzing), but HCl produces it much more rapidly.
Mg + 2HCl → MgCl₂ + H₂↑ (vigorous)
Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂↑ (slow)

Q11. Fresh milk has a pH of 6. How does the pH change as it turns to curd? Explain.

Answer: The pH decreases (becomes more acidic) as fresh milk turns to curd. Fresh milk has pH 6, which is slightly acidic. When milk turns to curd, the lactose (milk sugar) is converted to lactic acid by the action of Lactobacillus bacteria. This additional acid increases the H⁺ ion concentration, causing the pH to drop below 6 (typically around pH 4-5). The more the milk sours, the lower the pH.

Q12. A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a longer time to set as curd?

Answer:
(a) Baking soda (NaHCO₃) is a mild base. Adding it to fresh milk (pH 6) increases the pH to above 7 (slightly alkaline). This makes the milk mildly basic, which prevents the milk from becoming sour quickly because lactic acid produced by bacteria gets neutralised by the base. This is done to increase the shelf life of milk, especially in hot weather.
(b) The milk takes longer to set as curd because the added NaHCO₃ neutralises the lactic acid as it is being formed by bacteria. Since curd formation requires the accumulation of lactic acid (which lowers pH and causes the milk proteins to coagulate), the neutralisation slows this process down.

Q13. Plaster of Paris should be stored in a moisture-proof container. Explain why.

Answer: Plaster of Paris (CaSO₄·½H₂O) has the ability to absorb water (moisture) from the surroundings. When it absorbs water, it undergoes a chemical reaction and converts back into gypsum (CaSO₄·2H₂O), which is a hard solid mass:

\(\text{CaSO}_4 \cdot \tfrac{1}{2}\text{H}_2\text{O} + \tfrac{3}{2}\text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2\text{H}_2\text{O}\)

Once it sets as gypsum, it becomes useless for casting, moulding, or other purposes. Therefore, it must be stored in an air-tight, moisture-proof container to prevent premature setting.

Q14. What is a neutralisation reaction? Give two examples.

Answer: A neutralisation reaction is a chemical reaction in which an acid and a base react to form a salt and water. It is an exothermic process (releases heat).

Example 1:

\(\text{NaOH}(aq) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l)\)

Sodium hydroxide (base) + Hydrochloric acid → Sodium chloride (salt) + Water

Example 2:

\(\text{KOH}(aq) + \text{HNO}_3(aq) \rightarrow \text{KNO}_3(aq) + \text{H}_2\text{O}(l)\)

Potassium hydroxide (base) + Nitric acid → Potassium nitrate (salt) + Water

Q15. Give two important uses each of: (i) washing soda, and (ii) baking soda.

Answer:
(i) Uses of Washing Soda (Na₂CO₃·10H₂O):
1. It is used as a cleaning agent for domestic purposes — removing grease and stains from clothes and utensils.
2. It is used for softening hard water by removing dissolved calcium and magnesium salts. It reacts with them to form insoluble carbonates that can be filtered out.

(ii) Uses of Baking Soda (NaHCO₃):
1. It is used as an ingredient in baking powder — when heated, it releases CO₂ gas that makes bread and cakes soft and fluffy.
2. It is used as an antacid to neutralise excess stomach acid and relieve indigestion.

Group Activity: Make Your Own Indicator

Make a Natural Indicator from Red Cabbage or Beetroot

You can make your own acid-base indicator at home using red cabbage or beetroot. Here is how:

Take a few leaves of red cabbage (or slices of beetroot) and chop them finely.
Place them in a beaker and add enough water to cover the pieces. Boil for 10-15 minutes.
Filter the coloured solution into a clean bottle. This is your indicator.
Now test different household substances:
- Lemon juice, vinegar (acidic)
- Tap water (neutral)
- Soap solution, baking soda solution (basic)
Add a few drops of your indicator to each sample and record the colour changes.

Expected results with red cabbage indicator:

Solution	Nature	Colour
Lemon juice	Acidic	Red / Pink
Vinegar	Acidic	Red / Pink
Water	Neutral	Purple (no change)
Baking soda	Basic	Blue / Green
Soap solution	Basic	Green / Yellow

This activity demonstrates that many natural substances can act as pH indicators, changing colour in acidic versus basic environments.

Frequently Asked Questions — NCERT Exercises & Intext Questions

How do I solve NCERT Class 10 Science Chapter 2 (Acids, Bases and Salts) exercise questions for the CBSE board exam?

Solve NCERT Chapter 2 — Acids, Bases and Salts — exercise questions by first reading the question carefully, writing down the given data, recalling the relevant concepts like acids, bases, pH, and applying them step by step. This Part 4 covers every intext and end-of-chapter exercise from the NCERT textbook. Write balanced equations, label diagrams clearly and show each step — CBSE Class 10 board examiners award step marks even if the final answer has a small slip. Practising these solutions strengthens conceptual clarity and builds speed for the board exam.

Are the NCERT intext questions from Acids, Bases and Salts important for the Class 10 board exam?

Yes, NCERT intext questions for Chapter 2 Acids, Bases and Salts are highly important for the CBSE Class 10 Science board exam. Many board questions are directly lifted or only slightly modified from these intext questions, and they test the foundational concepts — acids, bases, pH — that chapter-end questions build on. Attempt every intext question first, then move on to the exercises. This practice ensures complete NCERT coverage, which is the CBSE exam's primary source.

What types of questions from Acids, Bases and Salts are asked in the CBSE Class 10 Science board exam?

The CBSE Class 10 board paper asks a mix of question types from Acids, Bases and Salts: 1-mark MCQ and assertion-reason, 2-mark short answers, 3-mark explanations, 5-mark long answers with diagrams or derivations, and 4-mark competency-based / case-study questions. These test understanding of acids, bases, pH, salts. Practising every NCERT exercise and intext question prepares you to answer all of these formats with confidence.

How many marks does Chapter 2 — Acids, Bases and Salts — carry in the Class 10 Science CBSE paper?

Chapter 2 — Acids, Bases and Salts — is part of the Class 10 Science syllabus and typically contributes 5–9 marks in the CBSE board paper, depending on the annual weightage. Questions are drawn from definitions, reasoning, numerical/descriptive problems and diagrams on topics like acids, bases, pH. Solving the NCERT exercises in this part is essential because CBSE directly references NCERT for question design.

Where can I find step-by-step NCERT solutions for Chapter 2 Acids, Bases and Salts Class 10 Science?

You can find complete, step-by-step NCERT solutions for Chapter 2 Acids, Bases and Salts Class 10 Science on MyAiSchool. Every intext and end-of-chapter exercise question is solved with full working, labelled diagrams and CBSE-aligned mark distribution. Solutions highlight key points about acids, bases, pH that examiners look for. This makes revision quick and exam-focused for Class 10 CBSE board students.

What is the best way to revise Acids, Bases and Salts before the Class 10 Science board exam?

The best way to revise Acids, Bases and Salts for the CBSE Class 10 Science board exam is a three-pass approach. First pass: skim the chapter and note down key terms like acids, bases, pH in a one-page mind map. Second pass: solve every NCERT intext and exercise question without looking at the solution, then self-check. Third pass: attempt previous CBSE board questions and competency-based questions under timed conditions. This structured revision secures full marks for this chapter.

AI Tutor

Science Class 10 — NCERT (2024-25)

Ready

Hi! 👋 I'm Gaura, your AI Tutor for Acids, Bases and Salts – NCERT Exercises. Take your time studying the lesson — whenever you have a doubt, just ask me! I'm here to help.