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The presence of… (Class 12 Chemistry SQP 2024-25, Q21)

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ChemistryCBSE Class 12 · Sample paper, session 2024-25 · 2 marks · Very short answer

CBSE Class 12 Chemistry sample paper 2024-25: question 21

From the official CBSE sample question paper for 2024-25, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerBiomolecules

The presence of Carbonyl group in glucose is confirmed by its reaction with hydroxylamine. Identify the type of carbonyl group present and its position. (1) Give a chemical reaction in support of your answer. (1)

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

Ketones are not oxidised by mild oxidising agents, but aldehydes are.

Hint 2

Which mild reagent converts glucose into a six-carbon monocarboxylic acid?

Hint 3

Name that acid and see which carbon carries its –COOH group.

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. The carbonyl group in glucose is an aldehyde (–CHO) group.

    ½ mark

  2. It is present at the C-1 (terminal) carbon of the six-carbon chain.

    ½ mark

  3. Supporting reaction: a mild oxidising agent, bromine water, oxidises glucose to gluconic acid, a six-carbon acid with –COOH at C-1. Only an aldehyde is oxidised so easily without breaking the chain, which confirms –CHO at C-1.
    (gluconic acid)

    1 mark

Answer: Aldehydic group at C-1; confirmed by oxidation with bromine water to gluconic acid

Where the marks are

  • Identifies the carbonyl group as aldehyde (½ mark)
  • Position C-1 (½ mark)
  • Reaction with bromine water giving gluconic acid, with equation (1 mark)

Revise the chapter

  • Chapter: Biomolecules (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Biomolecules, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: 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.