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1 mole of liquid A and 2… (Class 12 Chemistry 2023, Q7)

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ChemistryCBSE Class 12 · Board exam 2023, set 56/5/1 · 1 mark · MCQ

CBSE Class 12 Chemistry 2023: question 7

Set in the CBSE Class 12 board exam of 2023, paper 56/5/1, section A, question 7, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q7 · 1 mark · MCQSolutions

1 mole of liquid A and 2 moles of liquid B make a solution having a total vapour pressure 40 torr. The vapour pressure of pure A and pure B are 45 torr and 30 torr respectively. The above solution

  1. (A)is an ideal solution.
  2. (B)shows positive deviation.
  3. (C)shows negative deviation.
  4. (D)is a maximum boiling azeotrope.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 56/5/1.

Hints

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

Hint 1

Find the mole fractions of A and B first.

Hint 2

Use Raoult's law to work out what the vapour pressure would be if the solution were ideal.

Hint 3

The ideal value is 35 torr. The observed 40 torr is higher, so which kind of deviation is this?

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. Mole fractions: , .

  2. Ideal (Raoult's law) vapour pressure: torr.

  3. The observed vapour pressure (40 torr) is greater than the ideal value (35 torr), so the solution shows positive deviation from Raoult's law. Answer: (b).

    1 mark

Answer: (b) shows positive deviation

Where the marks are

  • Identifies option (b): observed VP 40 torr > ideal VP 35 torr, so positive deviation (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 paper2023 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.