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(a) State the following… (Class 12 Chemistry 2025, Q23)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2025: question 23

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section C, question 23, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 3 marks · Short answerElectrochemistry

(a) State the following :
(i) Kohlrausch law of independent migration of ions and
(ii) Faraday's first law of electrolysis.
(b) Using of X and Y given below, predict which is better for coating the surface of iron to prevent corrosion and why ?
Given V, V, V

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 56/1/1.

Hints

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

Hint 1

Kohlrausch's law concerns Λm° at infinite dilution and the ions' separate contributions.

Hint 2

Faraday's first law links the amount deposited to the charge passed.

Hint 3

A metal that protects iron must be oxidised more easily than iron. Compare the E° values.

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. (a)(i) Kohlrausch's law: the limiting molar conductivity of an electrolyte equals the sum of the individual contributions of its cation and anion, i.e. .

    1 mark

  2. (a)(ii) Faraday's first law: the amount of chemical reaction (mass of substance deposited or liberated) at an electrode during electrolysis is directly proportional to the quantity of electricity passed, i.e. .

    1 mark

  3. (b) X is better for coating iron.

    ½ mark

  4. V is more negative than V, so X is oxidised more readily than iron. X corrodes sacrificially and protects iron. Y ( V) is less easily oxidised than Fe and would not give this protection.

    ½ mark

Answer: (a) Statements of Kohlrausch's law and Faraday's first law; (b) X, since it has a more negative E° (higher oxidation potential) than Fe

Where the marks are

  • Correct statement of Kohlrausch's law (1 mark)
  • Correct statement of Faraday's first law (1 mark)
  • Chooses X (½ mark)
  • Reason: E° of X is more negative than that of Fe, so X is oxidised preferentially (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Electrochemistry, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 56/1/1: 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.