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(i) Distinguish with a… (Class 12 Chemistry 2023, Q35b)

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ChemistryCBSE Class 12 · Board exam 2023, set 56/1/1 · 5 marks · Long answer

CBSE Class 12 Chemistry 2023: question 35(b)

Set in the CBSE Class 12 board exam of 2023, paper 56/1/1, section E, question 35(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q35(b) · 5 marks · Long answerAldehydes, Ketones and Carboxylic Acids

(i) Distinguish with a suitable chemical test :
(1) and
(2) Ethanal and Ethanoic acid
(ii) Write the structure of oxime of acetone.
(iii) Identify A to D.
, and B D

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

For (i), look for a structural feature that only one compound in each pair has: a group in the first pair, an acidic –COOH group in the second.

Hint 2

For (ii), an oxime forms when replaces the carbonyl oxygen, and water is lost.

Hint 3

For (iii), recall what does to –COOH and what the Rosenmund reduction makes. Then decide whether a Grignard reagent or acting on an aldehyde gives a primary or a secondary alcohol.

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)(1) Butanone vs butanal: iodoform test

    Warm each compound with and NaOH solution.

    • Butanone, , is a methyl ketone, so it gives a yellow precipitate of iodoform:

    • Butanal, , has no group, so no yellow precipitate forms.

    (Tollens' test also works: butanal gives a silver mirror and butanone does not.)

    1 mark

  2. (i)(2) Ethanal vs ethanoic acid: sodium hydrogencarbonate test

    Add solution to each.

    • Ethanoic acid gives brisk effervescence of :

    • Ethanal gives no effervescence.

    (Alternatively, ethanal gives a silver mirror with Tollens' reagent and ethanoic acid does not.)

    1 mark

  3. (ii) Oxime of acetone

    Acetone condenses with hydroxylamine () with loss of water:

    The oxime (acetoxime) is .

    1 mark

  4. (iii) Identifying A and B

    • converts the acid into its acid chloride. **A = ** (ethanoyl chloride).
    • over Pd– (Rosenmund reduction) reduces the acid chloride to an aldehyde. **B = ** (ethanal).
    1 mark

  5. Identifying C and D

    • adds to ethanal, and hydrolysis then gives a secondary alcohol:

    . C = propan-2-ol.

    • reduces the aldehyde to a primary alcohol. **D = ** (ethanol).
    1 mark

Answer: (i)(1) Iodoform test: butanone gives a yellow ppt of , butanal does not; (i)(2) test: ethanoic acid gives effervescence, ethanal does not; (ii) ; (iii) A = , B = , C = , D =

Where the marks are

  • Correct test for butanone vs butanal (e.g. iodoform) with the observation for each compound (1 mark)
  • Correct test for ethanal vs ethanoic acid (e.g. ) with the observation for each compound (1 mark)
  • Structure of acetone oxime, (1 mark)
  • A = (½ mark)
  • B = (½ mark)
  • C = (½ mark)
  • D = (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Aldehydes, Ketones and Carboxylic Acids, 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.