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Common salt is a very… (Class 10 Science 2025, Q37)

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ScienceCBSE Class 10 · Board exam 2025, set 31/4/1 · 4 marks · Case-based

CBSE Class 10 Science 2025: question 37

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedAcids, Bases and Salts

Common salt is a very important chemical compound for our daily life. It's chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.

  1. (i)

    Name the acid and the base from which common salt can be obtained.

    1 mark
  2. (ii)

    State the nature (acidic/basic/neutral) of sodium chloride. Give reason for the justification for your answer.

    1 mark
  3. (iii)(A)

    What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained.

    2 marks

  4. OR

    (iii)(B)

    How is washing soda obtained from sodium chloride? Give chemical equation of the reactions involved in the process.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

A salt forms when an acid neutralises a base; split NaCl into its two parts to find them.

Hint 2

The pH of a salt depends on whether its parent acid and base are strong or weak.

Hint 3

For (iii), recall the chlor-alkali process, and how baking soda is heated and then recrystallised.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) Acid: hydrochloric acid (HCl). Base: sodium hydroxide (NaOH).

    1 mark

  2. (ii) Sodium chloride is neutral (pH 7), because it is a salt of a strong acid (HCl) and a strong base (NaOH).

    1 mark

  3. (iii)(A) When electricity is passed through brine, it decomposes (chlor-alkali process):

    ½ mark

  4. (iii)(A) Products and where they form: chlorine gas at the anode, hydrogen gas at the cathode, and sodium hydroxide solution near the cathode.

    1½ marks

  5. (iii)(B) Step 1: Brine is treated with ammonia and carbon dioxide, giving baking soda:

    ½ mark

  6. (iii)(B) Step 2: Sodium hydrogencarbonate is heated to give sodium carbonate:

    ½ mark

  7. (iii)(B) Step 3: Sodium carbonate is recrystallised from water to give washing soda.

    ½ mark

  8. (iii)(B) (washing soda)

    ½ mark

Answer: (i) HCl and NaOH; (ii) Neutral – salt of a strong acid and a strong base; (iii)(A) Brine decomposes: Cl₂ at the anode, H₂ at the cathode, NaOH near the cathode; (iii)(B) NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃; 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ on heating; Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O.

Where the marks are

  • Names HCl and NaOH (½ + ½ mark)
  • Nature neutral (½ mark) with reason: strong acid and strong base (½ mark)
  • States that brine decomposes on electrolysis (½ mark)
  • Cl₂ at anode, H₂ at cathode, NaOH near cathode (½ × 3 marks)
  • Washing soda: reaction forming NaHCO₃, heating to Na₂CO₃, recrystallisation, and the Na₂CO₃·10H₂O equation (½ × 4 marks)

Revise the chapter

Practise this chapterBoard-style questions from Acids, Bases and Salts, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/4/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.