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Answer the following. (Class 10 Science 2023, Q34B)

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ScienceCBSE Class 10 · Board exam 2023, set 31/4/1 · 5 marks · Long answer

CBSE Class 10 Science 2023: question 34(B)

Set in the CBSE Class 10 board exam of 2023, paper 31/4/1, 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

Answer the following.

  1. (i)

    What happens when a small piece of sodium is dropped in ethanol ? Write the equation for this reaction.

    1½ marks
  2. (ii)

    Why is glacial acetic acid called so ?

    1 mark
  3. (iii)

    What happens when ethanol is heated at 443 K in the presence of conc. ? Write the role of conc. in this case.

    1½ marks
  4. (iv)

    Write an equation showing saponification.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/4/1.

Hints

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

Hint 1

Think of what an active metal releases when it reacts with a compound having an –OH group.

Hint 2

For (ii), recall what happens to pure ethanoic acid around 290 K in winter.

Hint 3

At 443 K, hot conc. H₂SO₄ pulls water out of ethanol. For saponification, react an ester with NaOH.

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) Sodium reacts with ethanol, forming sodium ethoxide, and hydrogen gas is evolved with brisk effervescence.

    ½ mark

  2. (i) Equation: (sodium ethoxide + hydrogen)

    1 mark

  3. (ii) Pure ethanoic acid has a low melting point of 290 K (about 17 °C). In cold climates during winter it freezes into an ice-like solid, so it is called glacial acetic acid.

    1 mark

  4. (iii) Ethanol is dehydrated to ethene:

    1 mark

  5. (iii) Role of conc. : it acts as a dehydrating agent. It removes a water molecule from ethanol.

    ½ mark

  6. (iv) Saponification is the alkaline hydrolysis of an ester: (ethyl ethanoate gives sodium ethanoate and ethanol).

    1 mark

Answer: (i) H₂ gas evolves and sodium ethoxide forms: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂; (ii) it freezes at 290 K in winter, looking like ice; (iii) ethene forms, and conc. H₂SO₄ acts as a dehydrating agent; (iv) CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH

Where the marks are

  • States that hydrogen gas is evolved and sodium ethoxide is formed (½ mark)
  • Writes the equation for sodium and ethanol (1 mark)
  • Explains that the low melting point (290 K) makes the acid freeze in winter (1 mark)
  • States that ethene forms, with the equation (1 mark)
  • Gives the role of H₂SO₄ as a dehydrating agent (½ mark)
  • Writes the saponification equation of an ester with NaOH (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 paper2023 board paper, set 31/4/1: 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.