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Answer the following. (Class 10 Science 2023, Q34A)

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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(A)

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

Answer the following.

  1. (i)

    Draw the structure of the following compounds : (a) Butanoic acid (b) Chloropentane

    2 marks
  2. (ii)

    How are structure (i) and structure (ii) given below related to one another ? Give reason to justify your answer. Draw one more possible structure for above case. Structure (i): written as CH3 with CH–CH linked, i.e. . Structure (ii): .

    2 marks
  3. (iii)

    Differentiate between saturated and unsaturated carbon compounds on the basis of their general formula.

    1 mark

Figure in the paper: Structure (i): a central C–C bond with each carbon bearing two CH3 groups drawn as a condensed structural formula: CH3 at top-left and top-right, CH–CH bonded in middle, CH3 at bottom-left and bottom-right. Structure (ii): a central quaternary carbon bonded to three CH3 groups (top, left, bottom) and to CH2CH3 on the right. See it in the official paper.

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

'But-' means 4 carbons and 'pent-' means 5 carbons. The suffix '-oic acid' puts –COOH at the chain end.

Hint 2

Count the C and H atoms in both given structures. What do you notice?

Hint 3

Alkanes, alkenes and alkynes each have their own general formula in terms of n.

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)(a) Butanoic acid (): a chain of 4 carbons with the –COOH group on the end carbon.

    Expanded: H₃C–CH₂–CH₂–C(=O)–O–H. Each of the first three carbons carries its H atoms (3, 2, 2), and the last carbon has a double bond to O and a single bond to –OH.

    1 mark

  2. (b) Chloropentane (1-chloropentane, ): a 5-carbon chain with Cl on the end carbon.

    Expanded: each carbon has four single bonds; carbons 2–4 carry 2 H each, C-5 carries 2 H and Cl, and C-1 carries 3 H.

    1 mark

  3. (ii) Structure (i), , and structure (ii), , are structural isomers (chain isomers).

    ½ mark

  4. Reason: both have the same molecular formula but different arrangements of carbon atoms (different structures).

    ½ mark

  5. Another possible isomer is n-hexane:

    (or 2-methylpentane, )

    1 mark

  6. (iii) Saturated compounds (alkanes) have the general formula . Unsaturated compounds have (alkenes) or (alkynes). So in saturated compounds the number of H atoms is more than twice the number of C atoms; in unsaturated compounds it is equal to or less than twice.

    1 mark

Answer: (i) ; ; (ii) Isomers (same formula , different structures); e.g. n-hexane; (iii) Saturated , unsaturated /

Where the marks are

  • Correct structure of butanoic acid (1 mark)
  • Correct structure of chloropentane (1 mark)
  • Identifies them as isomers (½ mark)
  • Reason: same molecular formula, different structures (½ mark)
  • Draws one more correct isomer of (1 mark)
  • General formulae of saturated vs unsaturated compounds (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.