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(i) A solution is prepared… (Class 12 Chemistry 2026, Q31b)

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ChemistryCBSE Class 12 · Board exam 2026, set 56/5/1 · 5 marks · Long answer

CBSE Class 12 Chemistry 2026: question 31(b)

Set in the CBSE Class 12 board exam of 2026, paper 56/5/1, section E, question 31(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q31(b) · 5 marks · Long answerSolutions

(i) A solution is prepared by dissolving 0·025 g of potassium sulphate in 2 L of water at C. Assuming potassium sulphate is completely dissociated, determine its osmotic pressure. (3)
(Given : R = 0·082 L atm K mol, Molar mass of = 174 g mol)
(ii) What type of azeotrope will be formed by a solution of acetone and chloroform ? Give reason. (2)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 56/5/1.

Hints

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

Hint 1

Find from the ions given by K₂SO₄ and convert 27 °C to kelvin.

Hint 2

For (ii), think about whether acetone and chloroform attract each other more or less than their own molecules, and what that does to the vapour pressure.

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) , so .

    ½ mark

  2. , so

    ½ mark

  3. (with K)

    1 mark

  4. 1 mark

  5. (ii) Acetone and chloroform form a maximum boiling azeotrope.

    1 mark

  6. Reason: the mixture shows a large negative deviation from Raoult's law. The H of hydrogen-bonds with the O of acetone, so acetone–chloroform interactions are stronger than those in the pure liquids. The vapour pressure is therefore lowered and the boiling point is raised.

    1 mark

Answer: (i) π ≈ 5.3 × 10⁻³ atm; (ii) maximum boiling azeotrope (negative deviation due to H-bonding)

Where the marks are

  • i = 3 (½ mark)
  • Formula π = i n RT / V (½ mark)
  • Correct substitution (1 mark)
  • π = 5.3 × 10⁻³ atm (1 mark)
  • Maximum boiling azeotrope (1 mark)
  • Negative deviation / stronger acetone–chloroform interactions (1 mark)

Revise the chapter

  • Chapter: Solutions (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Solutions, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 56/5/1: 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.