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Science · 2026 · 5 marks
CBSE 2026 · Region 1 · Set 1 · Q29
(a) (i) Give reasons for the following: (I) Covalent compounds are poor conductor of electricity. (II) Soap does not form lather in hard water. (III)…
(i)
Give reasons for the following :
(I)
Covalent compounds are poor conductor of electricity.
(II)
Soap does not form lather in hard water.
(III)
Carbon shows catenation but silicon does not.
(ii)
Write chemical equations for the following :
(I)
Oxidation of ethanol by acidified $\displaystyle \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$.
(II)
Hydrogenation of ethene.
Mohan heated ethanol with a compound 'X' in the presence of a few drops of conc. $\displaystyle \mathrm{H}_{2} \mathrm{SO}_{4}$ and observed a sweet smelling compound 'Y' is formed. When 'Y' is treated with sodium hydroxide it gives back ethanol and a compound 'Z'.
(i)
Identify 'X', 'Y' and 'Z'.
(ii)
Write the role of conc. $\displaystyle \mathrm{H}_{2} \mathrm{SO}_{4}$ in the reaction.
(iii)
Write the chemical equations involved and name the reactions.
Marking-scheme solution
(i)
(I)
They do not give rise to charged particles/ ions.
(II)
Soap reacts with calcium and magnesium salts present in
hard water and forms insoluble substances called Scum.
(III)
$\displaystyle \mathrm{C}-\mathrm{C}$ bonds are strong and stable whereas $\displaystyle \mathrm{Si}-\mathrm{Si}$ bonds are
relatively weak.
(ii)(I)
$\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \xrightarrow{\text { acidified } \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\text { heat }} \mathrm{CH}_{3} \mathrm{COOH}$
(II)
$\displaystyle \mathrm{CH}_{2}=\mathrm{CH}_{2}+\mathrm{H}_{2} \xrightarrow{\mathrm{Ni}} \mathrm{CH}_{3}-\mathrm{CH}_{3}$
(i)
$\displaystyle \mathrm{X}-\mathrm{CH}_{3} \mathrm{COOH} /$ ethanoic acid /acetic acid
$\displaystyle \mathrm{Y}-\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5} / \mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3} /$ ester $\displaystyle /$ ethyl ethanoate
$\displaystyle \mathrm{Z}-\mathrm{CH}_{3} \mathrm{COONa} /$ sodium ethanoate $\displaystyle /$ sodium acetate
(ii)
Catalyst/ dehydrating agent
(iii)
Esterification reaction
$\displaystyle \mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{NaOH} \rightarrow \mathrm{CH}_{3} \mathrm{COONa}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$
Saponification reaction/ De-esterification reaction
All Carbon and its Compounds questions2026 question paperNCERT solutions: Carbon and its CompoundsPractice Carbon and its Compounds →
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CBSE Class 10 Science past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.