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Raina while doing… (Class 10 Science SQP 2023-24, Q34b)

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ScienceCBSE Class 10 · Sample paper, session 2023-24 · 5 marks · Long answer

CBSE Class 10 Science sample paper 2023-24: question 34(b)

From the official CBSE sample question paper for 2023-24, section D, question 34(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(b) · 5 marks · Long answerCarbon and its Compounds

Raina while doing certain reactions observed that heating of substance 'X' with vinegar like smell with a substance 'Y' (which is used as an industrial solvent) in presence of conc. Sulphuric acid on a water bath gives a sweet-smelling liquid 'Z' having molecular formula . When heated with caustic soda (), 'Z' gives back the sodium salt of and the compound 'Y'.

Identify 'X', 'Y', and 'Z'. Illustrate the changes with the help of suitable chemical equations.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Which acid is present in vinegar? Which common alcohol is used as an industrial solvent?

Hint 2

An acid and an alcohol heated with conc. sulphuric acid give a sweet-smelling ester. Count the carbon atoms to fit .

Hint 3

Heating an ester with NaOH is saponification. It gives the sodium salt of the acid and the alcohol back.

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. Identifying X: X has a vinegar-like smell. Vinegar is a dilute (5–8%) solution of ethanoic acid, so X is **ethanoic acid (acetic acid), **.

    1 mark

  2. Identifying Y: Y is used as an industrial solvent and reacts with an acid to give an ester, so Y is an alcohol: **ethanol (ethyl alcohol), **.

    1 mark

  3. Identifying Z: A sweet-smelling liquid formed from an acid and an alcohol is an ester. With formula , Z is **ethyl ethanoate, **. Check: carbons , hydrogens , oxygens .

    1 mark

  4. Formation of Z (esterification):

    The acid (X) and the alcohol (Y) give the ester (Z). Conc. acts as the catalyst.

    1 mark

  5. Action of caustic soda on Z (saponification):

    The ester gives back sodium ethanoate (the sodium salt of X) and ethanol (Y).

    1 mark

Answer: X = ethanoic acid (); Y = ethanol (); Z = ethyl ethanoate (). Esterification: (conc. ). Saponification: .

Where the marks are

  • Identifies X as ethanoic acid (1 mark)
  • Identifies Y as ethanol (1 mark)
  • Identifies Z as ethyl ethanoate (ester) (1 mark)
  • Correct esterification equation with conc. (1 mark)
  • Correct equation for hydrolysis of the ester by NaOH giving sodium ethanoate and ethanol (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Carbon and its Compounds, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2023-24: 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.