Skip to content

Arrange the products… (Class 12 Chemistry SQP 2025-26, Q26)

questionbuddy.in/q/cbse-12-chemistry-2025-26-sqp-q26-arrange-products-obtained-cases-increasing

ChemistryCBSE Class 12 · Sample paper, session 2025-26 · 3 marks · Short answer

CBSE Class 12 Chemistry sample paper 2025-26: question 26

From the official CBSE sample question paper for 2025-26, section C, question 26, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26 · 3 marks · Short answerAldehydes, Ketones and Carboxylic Acids

Arrange the products obtained in the following cases in the increasing order of their pKa values:
A. Oxidation of ethanol in presence of acidified potassium dichromate
B. Reaction of propanoic acid with in the presence of red Phosphorus
C. Reaction of isopropyl magnesium bromide with carbon dioxide, followed by hydrolysis.
D. Reaction of propanoic acid with in the presence of red Phosphorous.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Identify each product first; B and D are HVZ reactions, and C is a Grignard reagent reacting with CO₂.

Hint 2

Lower pKa means a stronger acid; compare the –I effects of Cl and Br with the +I effect of alkyl groups.

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. (ethanoic acid)

    ½ mark

  2. B. (2-bromopropanoic acid; HVZ reaction)

    ½ mark

  3. C. (2-methylpropanoic acid)

    ½ mark

  4. D. (2-chloropropanoic acid)

    ½ mark

  5. Halogen at the α-carbon withdraws electrons (–I), stabilising the carboxylate ion; Cl (more electronegative) does this more than Br. Alkyl groups (+I) destabilise the anion. Acid strength: D > B > A > C, so the increasing order of pKa is:

    1 mark

Answer: pKa: CH₃CHClCOOH (D) < CH₃CHBrCOOH (B) < CH₃COOH (A) < (CH₃)₂CHCOOH (C)

Where the marks are

  • Product A: CH₃COOH (½ mark)
  • Product B: CH₃CHBrCOOH (½ mark)
  • Product C: (CH₃)₂CHCOOH (½ mark)
  • Product D: CH₃CHClCOOH (½ mark)
  • Correct increasing order of pKa (1 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 paperSample paper 2025-26: 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.