Question Bank — Acids, Bases and Salts

NCERT Class 10 Science · Chapter 2 · CBSE Board Pattern

Class 10 Science Chapter 2 Question Bank CBSE Board Pattern

Section A — MCQs (10 questions, 1 mark each)

  1. Which of the following will turn blue litmus red?
    (a) NaOH solution (b) NH₄OH solution (c) CH₃COOH solution (d) Na₂CO₃ solution

  2. When zinc granules react with dilute H₂SO₄, the gas evolved is
    (a) oxygen (b) hydrogen (c) carbon dioxide (d) sulphur dioxide

  3. Assertion (A): Dry HCl gas does not change the colour of dry blue litmus paper.
    Reason (R): Hydrogen ions are produced only in the presence of water.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  4. A solution has pH = 9. The solution is
    (a) strongly acidic (b) weakly acidic (c) neutral (d) weakly basic

  5. Bleaching powder is prepared by the action of chlorine on
    (a) dry slaked lime (b) washing soda (c) baking soda (d) rock salt

  6. Assertion (A): Sodium carbonate is a basic salt.
    Reason (R): It is formed from a strong base and a weak acid.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  7. Which of the following is an olfactory indicator?
    (a) Phenolphthalein (b) Methyl orange (c) Vanilla essence (d) Litmus

  8. Plaster of Paris is obtained by heating gypsum at
    (a) 373 K (b) 473 K (c) 573 K (d) 673 K

  9. When excess CO₂ is passed through lime water, the precipitate formed
    (a) remains insoluble (b) dissolves to form calcium hydrogencarbonate (c) forms calcium chloride (d) forms calcium oxide

  10. The pH of a neutral solution is
    (a) 0 (b) 7 (c) 10 (d) 14

Section B — Very Short Answer (6 questions, 2 marks each)

  1. Why should curd or sour substances not be kept in brass or copper vessels? Give the chemical reason.

  2. Name the products formed when sodium hydrogencarbonate is heated. Write the balanced chemical equation.

  3. What is meant by water of crystallisation? Give one example of a salt that contains water of crystallisation.

  4. Distinguish between a strong acid and a weak acid on the basis of the number of H⁺ ions produced in aqueous solution.

  5. Write the chemical formula of washing soda. How is it obtained from sodium carbonate?

  6. What happens when a metal oxide reacts with an acid? Give one example with balanced equation.

Section C — Short Answer (3 marks each)

  1. A student added dilute HCl to sodium carbonate in one test tube and to sodium hydrogencarbonate in another. Write the observations and balanced equations for both reactions. How will the gas evolved be tested?

  2. With the help of a labelled diagram, describe the activity to show that an acid solution in water conducts electricity. Name the ions responsible for conduction.

  3. What is the chlor-alkali process? Write the chemical equation involved and state the uses of any two products obtained.

  4. Explain why the pH of the mouth falling below 5.5 leads to tooth decay. How can this be prevented?

  5. A farmer finds that the soil in his field is too acidic. Which substances would you suggest he add to the soil and why? Name two such substances.

Section D — Long Answer (3 questions, 5 marks each)

  1. (a) Draw a neat labelled diagram of the apparatus used to show the reaction of zinc granules with dilute sulphuric acid and to test the gas evolved. (3 marks)
    (b) Write the balanced chemical equation for the reaction. (1 mark)
    (c) What happens when the same experiment is repeated with sodium hydroxide solution instead of the acid? (1 mark)

  2. (a) What are the different types of salts on the basis of the strength of the acid and base from which they are formed? Give one example of each type with approximate pH. (3 marks)
    (b) How will you prepare bleaching powder? Write the balanced equation and state two uses. (2 marks)

  3. Describe the preparation of sodium hydroxide from common salt. Name the process and write the balanced chemical equation. State the industrial importance of the three products obtained in this process.

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

A student collected soil samples from different parts of a garden and tested their pH using universal indicator paper. He observed that the soil from the rose bed had pH 5.5 while the soil from the spinach patch had pH 7.5. He also noted that plants in the rose bed were not growing well.

Sub-questions:
(i) Which soil sample is acidic and which is basic?
(ii) Which substance would you advise the student to add to the rose-bed soil to improve plant growth?
(iii) Why do different plants require different soil pH for healthy growth?
(iv) Name one natural indicator that could have been used instead of universal indicator paper.

Case 2

During a laboratory activity, a teacher demonstrated that when concentrated sulphuric acid is added slowly to water in a beaker, the beaker becomes hot. She warned students never to add water to concentrated acid.

Sub-questions:
(i) What type of process is taking place when an acid is mixed with water?
(ii) Why is it dangerous to add water to concentrated acid?
(iii) How does dilution affect the concentration of H₃O⁺ ions?
(iv) Name another substance whose dissolution in water is also highly exothermic.

Section F — HOTS and Application (4 questions, 3 marks each)

  1. Predict-and-justify: What would happen if excess sodium hydroxide solution is added to a solution of copper(II) sulphate? Justify your answer with a balanced chemical equation and state the nature of the final solution.

  2. Analyse an unexpected observation: In an experiment, two solutions of equal concentration—one of HCl and the other of CH₃COOH—were taken in separate test tubes and zinc granules were added. More vigorous fizzing was observed in the HCl test tube. Explain this observation.

  3. Apply to an unfamiliar real-life situation: A person accidentally spills concentrated NaOH pellets on the laboratory table. Suggest the safest way to clean the spill using substances commonly available in a chemistry laboratory. Give reasons for your choice.

  4. Compare two situations: Two test tubes contain equal volumes of dilute HCl. In the first test tube, a few drops of phenolphthalein are added and NaOH solution is added dropwise until the solution turns pink. In the second test tube, the same amount of NaOH is added without indicator. In which test tube will the final solution show a higher pH and why?

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Section A

  1. (c)
  2. (b)
  3. (a)
  4. (d)
  5. (a)
  6. (a)
  7. (c)
  8. (a)
  9. (b)
  10. (b)

Section B

  1. Acids present in curd/sour substances react with metals (Cu, Zn) of the vessel forming poisonous salts. (definition + reason — 2 marks)
  2. Na₂CO₃ + H₂O + CO₂ (or balanced equation) — 1 mark; products named — 1 mark.
  3. Fixed number of water molecules in one formula unit of salt; example CuSO₄·5H₂O — 2 marks.
  4. Strong acid produces more H⁺ ions; weak acid produces fewer H⁺ ions in same concentration — 2 marks.
  5. Na₂CO₃·10H₂O; by recrystallisation of Na₂CO₃ — 2 marks.
  6. Salt + water formed (general equation); example CuO + 2HCl → CuCl₂ + H₂O — 2 marks.

Section C

  1. Both produce CO₂ (effervescence) — 1 mark; equations — 1 mark; test with lime water — 1 mark.
  2. Diagram with nails, battery, bulb — 2 marks; glowing shows conduction; H⁺ and anions carry current — 1 mark.
  3. Electrolysis of brine (chlor-alkali) — 1 mark; equation — 1 mark; uses of NaOH and Cl₂/H₂ — 1 mark.
  4. Below pH 5.5 enamel (calcium hydroxyapatite) corrodes; bacteria produce acids from food; prevented by brushing with basic toothpaste — 3 marks.
  5. Quick lime or slaked lime or chalk (any two) — 1 mark; they neutralise excess acid, raise pH — 2 marks.

Section D

  1. (a) Labelled diagram (test tube, delivery tube, soap solution, candle) — 3 marks; (b) Zn + H₂SO₄ → ZnSO₄ + H₂ — 1 mark; (c) H₂ also evolved (NaOH + Zn → sodium zincate + H₂) — 1 mark.
  2. (a) Three types with examples and pH — 3 marks; (b) Ca(OH)₂ + Cl₂ → Ca(ClO)₂ + …; two uses — 2 marks.
  3. Chlor-alkali process description + equation — 3 marks; industrial uses of three products — 2 marks.

Section E

Case 1: (i) Rose-bed acidic, spinach basic — 1 mark; (ii) slaked lime/quick lime — 1 mark; (iii) each plant has optimum pH range for nutrient absorption — 1 mark; (iv) red cabbage/turmeric — 1 mark.
Case 2: (i) Exothermic — 1 mark; (ii) violent splashing/burns — 1 mark; (iii) H₃O⁺ concentration decreases — 1 mark; (iv) NaOH — 1 mark.

Section F

  1. Blue ppt of Cu(OH)₂ forms; CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄; final solution basic — reasoning chain.
  2. HCl is strong acid → more H⁺ ions → faster reaction; CH₃COOH weak → fewer H⁺ ions.
  3. Cover with sand/dilute acid slowly or wash with plenty of water; avoid direct contact.
  4. First test tube (with indicator) will have exactly pH 7 (neutralisation complete); second will be basic (excess NaOH) — comparison and justification.
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All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.