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Science · 2022 · 3 marks
CBSE 2022 · Region 3 · Set 1 · Q9
(a) State the reason why (i) carbon compounds have low melting and boiling points. (ii) carbon compounds do not conduct electricity. (iii) carbon can…
(a)
State the reason why
(i)
carbon compounds have low melting and boiling points.
(ii)
carbon compounds do not conduct electricity.
(iii)
carbon can form only covalent compounds.
OR
(b)
What is a homologous series? Find the difference in molecular mass between the two consecutive members of a homologous series. State how in a homologous series of carbon compounds the following properties vary with increase in molecular mass:
(i)
Melting and boiling points
(ii)
Chemical properties
Marking-scheme solution
(a)
(i) The forces of attraction between the molecules are weak.
(ii) Bonding in carbon compounds does not give rise to any charged particles.
(iii) Carbon only shares electrons with other atoms. It is not able to lose four electrons or gain four electrons.
A series of compounds in which some functional groups substitute for hydrogen in a carbon chain / the succeeding members differ by \(\displaystyle -\mathrm{CH}_{2}\) unit ($\displaystyle 14$ u)
Difference of \(\displaystyle \mathrm{CH}_{2}=12 \mathrm{u}+2 \mathrm{u}=14 \mathrm{u}\)
(i) Melting and boiling points increase with increase in molecular mass.
(ii) Chemical properties, determined by the functional group remain same in a homologous series.
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CBSE Class 10 Science past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.