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A 5% solution of… (Class 12 Chemistry SQP 2023-24, Q18)

questionbuddy.in/q/cbse-12-chemistry-2023-24-sqp-q18-solution-isotonic-solution-non-electrolytic

ChemistryCBSE Class 12 · Sample paper, session 2023-24 · 2 marks · Very short answer

CBSE Class 12 Chemistry sample paper 2023-24: question 18

From the official CBSE sample question paper for 2023-24, section B, question 18, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18 · 2 marks · Very short answerSolutions

A 5% solution of (MW = 322) is isotonic with 2% solution of non-electrolytic, non volatile substance X. Find out the molecular weight of X.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Isotonic means equal osmotic pressure at the same temperature.

Hint 2

The salt is an electrolyte — count the ions it gives to find i.

Hint 3

Both solutions are per 100 mL, so moles = mass/molar mass can be compared directly.

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. Isotonic solutions have equal osmotic pressure: , i.e. , so .

    ½ mark

  2. , so ; X is a non-electrolyte, .

    ½ mark

  3. Taking 100 mL of each solution:

    ½ mark

  4. ½ mark

Answer: Molecular mass of X ≈ 42.9 g mol⁻¹

Where the marks are

  • Uses equal osmotic pressure for isotonic solutions, iC₁ = C₂ (½ mark)
  • Takes i = 3 for Na₂SO₄·10H₂O (½ mark)
  • Correct substitution 3 × 5/322 = 2/M (½ mark)
  • M = 42.9 g mol⁻¹ (½ 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 paperSample paper 2023-24: 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.