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Define Azeotrope. What… (Class 12 Chemistry 2025, Q17B)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 2 marks · Very short answer

CBSE Class 12 Chemistry 2025: question 17(B)

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section B, question 17(B), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q17(B) · 2 marks · Very short answerSolutions

Define Azeotrope. What type of Azeotrope is formed by negative deviation from Raoult's law ? Give an example.

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

Think of a mixture that distils over without any change in composition.

Hint 2

Negative deviation lowers the vapour pressure; what does that do to the boiling point?

Hint 3

A common example involves nitric acid and water.

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. Azeotropes are binary liquid mixtures that have the same composition in the liquid phase and in the vapour phase and boil at a constant temperature. They therefore cannot be separated by fractional distillation.

    1 mark

  2. A solution showing large negative deviation from Raoult's law forms a maximum boiling azeotrope.

    ½ mark

  3. Example: nitric acid and water, about 68% and 32% water by mass, which boils at about 393.5 K.

    ½ mark

Answer: Azeotrope: a constant-boiling mixture with the same composition in liquid and vapour; negative deviation gives a maximum boiling azeotrope, e.g. 68% HNO₃ + 32% H₂O

Where the marks are

  • Definition: same composition in liquid and vapour, boils at constant temperature (1 mark)
  • Maximum boiling azeotrope (½ mark)
  • Correct example, e.g. HNO₃–water (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 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.