(A) A carbon compound 'A' on heating with excess conc. $H_2SO_4$ 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 2 moles of carbon dioxide and 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'.

OR

(B) A carbon compound 'A' is widely used as a preservative in pickles and has a molecular formula $C_2H_4O_2$. 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.

(A) The compound 'A' is ethanol $CH_3CH_2OH$. On heating with excess conc. $H_2SO_4$, it forms ethene $CH_2=CH_2$ (compound 'B'). Ethene on addition of one mole of hydrogen gas in the presence of nickel catalyst forms ethane $CH_3CH_3$ (compound 'C'). Ethane on combustion in air forms 2 moles of carbon dioxide and 3 moles of water.

$CH_3CH_2OH {->[H_2SO_4]} CH_2=CH_2 {->[H_2/Ni]} CH_3CH_3 {->[O_2]} 2CO_2 + 3H_2O$

Concentrated sulphuric acid acts as a dehydrating agent in the formation of ethene from ethanol.

OR

(B) (i) The compound 'A' is ethanoic acid $CH_3COOH$.

$CH_3COOH$

(ii) Ethanoic acid reacts with ethanol to form ethyl ethanoate $CH_3COOC_2H_5$ (compound 'B').

$CH_3COOH + C_2H_5OH {->[H^+]} CH_3COOC_2H_5 + H_2O$

The presence of an acid acts as a catalyst in the reaction.

(iii) Ethyl ethanoate on hydrolysis in the presence of an acid or a base gives back ethanoic acid.

$CH_3COOC_2H_5 + H_2O {->[H^+]} CH_3COOH + C_2H_5OH$

(iv) Ethanoic acid can be obtained from ethanol by oxidation.

$CH_3CH_2OH {->[O]} CH_3CHO {->[O]} CH_3COOH$

(v) The gas produced when ethanoic acid reacts with washing soda is carbon dioxide.

$CH_3COOH + Na_2CO_3 ightarrow CH_3COONa + H_2O + CO_2$