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Science · 2025 · 5 marks
CBSE 2025 · Region 4 · Set 1 · Q34
(A) A carbon compound 'A' on heating with excess conc. H_2 SO_4 forms a compound 'B', which on addition of one mole of hydrogen gas in the presence…
A carbon compound 'A' on heating with excess conc. $\displaystyle \mathrm{H}_{2} \mathrm{SO}_{4}$ forms a compound 'B', which on addition of one mole of hydrogen gas in the presence of nickel catalyst forms a compound 'C'. 'C' on combustion in air forms $\displaystyle 2$ moles of carbon dioxide and $\displaystyle 3$ moles of water. Identify 'A', 'B' and 'C' and write their structures. Give chemical equations of the reactions involved. Also state the role of concentrated sulphuric acid in the formation of 'B' from 'A'.
A carbon compound 'A' is widely used as a preservative in pickles and has a molecular formula $\displaystyle \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}$. This compound reacts with ethanol to form a sweet smelling compound 'B'.
(i)
Identify the compound 'A' and write its structure.
(ii)
Write the chemical equation for the reaction of 'A' with ethanol to form compound 'B'. State the role of presence of an acid in the reaction.
(iii)
How can we get compound 'A' back from 'B' ?
(iv)
How can 'A' be obtained from ethanol ?
(v)
Name the gas produced when compound 'A' reacts with washing soda.
Marking-scheme solution
Compound A: Ethanol / Ethyl alcohol ; / \(\displaystyle \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\)
Compound B: Ethene ; / \(\displaystyle \mathrm{C}_{2}\mathrm{H}_{4}\)
Compound C: Ethane ; / \(\displaystyle \mathrm{C}_{2}\mathrm{H}_{6}\)
\[\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH} \xrightarrow{\text{Hot Conc } \mathrm{H}_{2}\mathrm{SO}_{4}} \mathrm{CH}_{2}=\mathrm{CH}_{2} + \mathrm{H}_{2}\mathrm{O}
\]
'A' \(\) 'B'
Conc. \(\displaystyle \mathrm{H}_{2}\mathrm{SO}_{4}\) is a dehydrating agent.
\(\displaystyle +\ \mathrm{H}_{2} \xrightarrow{\text{Ni}} \mathrm{CH}_{3}-\mathrm{CH}_{3}\)
'B' \(\) 'C'
\[\mathrm{C}_{2}\mathrm{H}_{6} + 7/2\ \mathrm{O}_{2} \longrightarrow 2\mathrm{CO}_{2} + 3\mathrm{H}_{2}\mathrm{O}
\]
(i)
A - Ethanoic acid ; / \(\displaystyle \mathrm{CH}_{3}\mathrm{COOH}\)
(ii)
\[\mathrm{CH}_{3}\mathrm{COOH} + \mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH} \xrightarrow{\text{acid}} \mathrm{CH}_{3}\mathrm{COOC}_{2}\mathrm{H}_{5}
\]
'A' \(\displaystyle \) 'B' \(\) Role of acid - As a catalyst
(iii) By adding dil. NaOH to B (ester) / saponification / by adding water with acid or base / on addition of NaOH, sodium salt of acid is produced which is further hydrolysed to form 'A'.
(iv) By adding solution of alkaline potassium permanganate or acidified potassium dichromate in warm ethanol. /
\[\mathrm{CH}_{3}-\mathrm{CH}_{2}\mathrm{OH} \xrightarrow[\text{Or acidified } \mathrm{K}_{2}\mathrm{Cr}_{2}\mathrm{O}_{7} + \text{Heat}]{\text{Alkaline } \mathrm{KMnO}_{4}} \mathrm{CH}_{3}\mathrm{COOH}
\]
(v) Carbon dioxide / \(\displaystyle \mathrm{CO}_{2}\)
All Carbon and its Compounds questions2025 question paperNCERT solutions: Carbon and its CompoundsPractice Carbon and its Compounds →
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.