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(a) CH_3-CH(OH)-CH_3 PCl_5… (Class 12 Chemistry 2023, Q22)

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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 22

Set in the CBSE Class 12 board exam of 2023, paper 56/1/1, section B, question 22, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 2 marks · Very short answerHaloalkanes and Haloarenes

(a)
(b)
Identify 'A' and 'B' in the above reactions.

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

PCl₅ converts an alcohol into an alkyl chloride.

Hint 2

AgCN is covalent, so think about which atom of the cyanide group bonds to carbon.

Hint 3

Alcoholic KOH eliminates HX; then apply Markovnikov's rule for HBr addition.

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. (a) replaces –OH by –Cl. **A = (2-chloropropane).**

    ½ mark

  2. AgCN is mainly covalent, so it attacks through the nitrogen atom and gives an isocyanide. **B = (2-propyl isocyanide / isopropyl isocyanide).**

    ½ mark

  3. (b) Alcoholic KOH causes dehydrohalogenation. **A = (propene).**

    ½ mark

  4. HBr adds by Markovnikov's rule, so Br goes to the carbon with fewer H atoms. **B = (2-bromopropane).**

    ½ mark

Answer: (a) A = 2-chloropropane, B = 2-propyl isocyanide (CH₃CH(NC)CH₃); (b) A = propene, B = 2-bromopropane

Where the marks are

  • (a) A = 2-chloropropane (½ mark)
  • (a) B = isopropyl isocyanide (½ mark)
  • (b) A = propene (½ mark)
  • (b) B = 2-bromopropane (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Haloalkanes and Haloarenes, 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.