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Answer the following. (Science 2024 31/2/1 Q34a)

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ScienceCBSE Class 10 · Board exam 2024, set 31/2/1 · 5 marks · Long answer

CBSE Class 10 Science 2024: question 34(a)

Set in the CBSE Class 10 board exam of 2024, paper 31/2/1, 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)

    Give reason why carbon can neither form cations nor anions but form covalent compounds.

    0 marks
  2. (ii)

    What is homologous series of carbon compound ? Write the molecular formula of any two consecutive members of homologous series of aldehydes.

    0 marks
  3. (iii)

    Draw the structure of the molecule of cyclohexane ().

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/2/1.

Hints

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

Hint 1

Compare the energy needed to lose 4 electrons with the difficulty of holding 4 extra electrons.

Hint 2

Aldehydes have the –CHO group; consecutive members differ by one .

Hint 3

Cyclohexane is a saturated ring of six carbons; count the hydrogens on each carbon.

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) Carbon has 4 valence electrons. To form it would have to lose 4 electrons, which needs a very large amount of energy. To form it would have to gain 4 electrons, and a nucleus with only 6 protons would find it hard to hold 10 electrons.

    1 mark

  2. So carbon completes its octet by sharing its valence electrons with other atoms, forming covalent bonds and covalent compounds.

    1 mark

  3. (ii) A homologous series is a series of carbon compounds in which the same functional group replaces hydrogen in a carbon chain. Members have similar chemical properties, and successive members differ by a unit (14 u in mass).

    1 mark

  4. Two consecutive aldehydes: ethanal, (), and propanal, (). Methanal, HCHO, and ethanal, , are also correct.

    1 mark

  5. (iii) Structure of cyclohexane (described): Six carbon atoms are joined by single bonds in a closed hexagonal ring. Each carbon is bonded to its two neighbouring carbons and to two hydrogen atoms, so each corner is a group. In total there are 6 C–C single bonds and 12 C–H bonds.

    1 mark

Answer: (i) Losing or gaining 4 electrons is energetically too difficult, so carbon shares electrons and forms covalent bonds; (ii) homologous series: same functional group, similar properties, successive members differ by ; e.g. and ; (iii) hexagonal ring of six groups joined by single bonds.

Where the marks are

  • Explains why and do not form (1 mark)
  • States that carbon shares electrons and forms covalent compounds (1 mark)
  • Definition of homologous series (1 mark)
  • Two consecutive aldehyde formulae (½ + ½ mark)
  • Correct structure of cyclohexane with all 12 H atoms (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 paper2024 board paper, set 31/2/1: 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.