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A saturated organic compound… (Class 10 Science 2023, Q34a)

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

CBSE Class 10 Science 2023: question 34(a)

Set in the CBSE Class 10 board exam of 2023, paper 31/1/1, section D, question 34(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

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

A saturated organic compound 'A' belongs to the homologous series of alcohols.
On heating 'A' with concentrated sulphuric acid at 443 K, it forms an unsaturated compound 'B' with molecular mass 28 u.
The compound 'B' on addition of one mole of hydrogen in the presence of Nickel, changes to a saturated hydrocarbon 'C'.

  1. (i)

    Identify A, B and C.

    0 marks
  2. (ii)

    Write the chemical equations showing the conversion of A into B.

    0 marks
  3. (iii)

    What happens when compound C undergoes combustion ?

    0 marks
  4. (iv)

    State one industrial application of hydrogenation reaction.

    0 marks
  5. (v)

    Name the products formed when compound A reacts with sodium.

    0 marks

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

Hints

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

Hint 1

Use the molecular mass 28 u of B to find which alkene it is.

Hint 2

An alkene forms from an alcohol by losing water. Which alcohol has the same number of carbons as B?

Hint 3

Adding H₂ across a double bond gives the alkane. Alcohols react with Na much as water does, giving an alkoxide and H₂.

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) B is an unsaturated compound with molecular mass 28 u. For an alkene : . So **B = ethene, **.

    ½ mark

  2. Ethene is formed by dehydration of an alcohol with the same number of carbon atoms. So **A = ethanol (ethyl alcohol), **.

    ½ mark

  3. Adding one mole of (Ni catalyst) to ethene gives a saturated hydrocarbon. So **C = ethane, **: .

    ½ mark

  4. (ii) Dehydration of ethanol with hot concentrated sulphuric acid. The acid acts as a dehydrating agent and removes water:

    1 mark

  5. (iii) Ethane burns in air or oxygen to give carbon dioxide and water. A large amount of heat (and light) is released:

    1 mark

  6. (iv) Hydrogenation is used in industry to convert vegetable oils into vegetable ghee (solid fats), using a nickel catalyst.

    ½ mark

  7. (v) Ethanol reacts with sodium to give sodium ethoxide and hydrogen gas:

    1 mark

Answer: (i) A = ethanol (CH₃CH₂OH), B = ethene (CH₂=CH₂), C = ethane (C₂H₆); (ii) CH₃CH₂OH → CH₂=CH₂ + H₂O (hot conc. H₂SO₄, 443 K); (iii) CO₂ and H₂O are formed with release of a lot of heat; (iv) converting vegetable oils into vegetable ghee (fats); (v) sodium ethoxide and hydrogen

Where the marks are

  • Identifies A as ethanol (½ mark)
  • Identifies B as ethene (½ mark)
  • Identifies C as ethane (½ mark)
  • Equation for dehydration of ethanol with conc. H₂SO₄ at 443 K (1 mark)
  • States that CO₂ and water form with release of a large amount of heat; an unbalanced equation is accepted (1 mark)
  • Hydrogenation of vegetable oils to fats/ghee (½ mark)
  • Names sodium ethoxide and hydrogen (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 31/1/1: 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.