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On diluting two… (Class 12 Chemistry 2023, Q20a)

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ChemistryCBSE Class 12 · Board exam 2023, set 56/1/1 · 2 marks · Very short answer

CBSE Class 12 Chemistry 2023: question 20(a)

Set in the CBSE Class 12 board exam of 2023, paper 56/1/1, section B, question 20(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q20(a) · 2 marks · Very short answerElectrochemistry

On diluting two electrolytes 'A' and 'B', the of 'A' increases 25 times while that of 'B' increases by 1·5 times. Which of the two electrolytes is strong ? Justify your answer graphically.

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

Hints

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

Hint 1

A strong electrolyte is almost completely ionised even at moderate concentration.

Hint 2

Which electrolyte's degree of ionisation would change a lot on dilution?

Hint 3

Plot against for both types and compare the shapes.

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. 'B' is the strong electrolyte. A strong electrolyte is already almost fully ionised, so dilution only slightly increases (here by 1·5 times). Ion–ion attraction decreases on dilution, which raises a little. A weak electrolyte ('A') ionises much more on dilution, so its rises steeply (25 times).

    1 mark

  2. **Graph ( on the y-axis vs on the x-axis):**

    • For B (strong electrolyte) the graph is a straight line with a small negative slope. It obeys and can be extrapolated to to give .
    • For A (weak electrolyte) the curve stays low at higher concentrations. It then rises very sharply as and cannot be extrapolated.
    1 mark

Answer: B is the strong electrolyte (Λm rises only slightly and linearly with dilution; A shows a steep rise and is weak).

Where the marks are

  • Identifies B as the strong electrolyte with reason (1 mark)
  • Correct graph of vs : linear, gentle slope for B and steep curve near zero for A (1 mark)

Revise the chapter

  • Chapter: Electrochemistry (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Electrochemistry, one at a time, marked against the answer key and marking points.Back to the full paper2023 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.