Question

(a) Write the functional groups present in an aldehyde and a carboxylic acid.
(b) How would you distinguish between an alcohol and a carboxylic acid?
(c) What happens when ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid? Write equation of the reaction involved.
(d) What happens when a piece of sodium metal is added to ethanol? Write equation of the reaction which takes place.
​(e) Describe how ethene can be prepared from ethanol? Give an equation of the reaction and state the conditions.

Answer 1

(a) The functional group present in an aldehyde will be carbonyl group and in carboxylic acid will be carboxyl group.

(b) Ethanol and ethanoic acid can be distinguished by reaction with sodium hydroxide. Ethanol does not react with sodium hydroxide, but ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.
${\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{H}}_2\mathrm{O}$
Ethanol has a sweet and pleasant smell but ethanoic acid has a pungent odour.

(c) When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, we will get a sweet smelling ester ethyl ethanoate.
${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{CH}}_3\mathrm{COOH}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}$

(d) When a piece of sodium metal is added to ethanol, sodium ethoxide is formed with the evolution of hydrogen gas.
$2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+2\mathrm{Na}\to 2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}+{\mathrm{H}}_2$

(e) By acidic hydrolysis of ethanol, dehydration of ethanol will occur which lead to the formation of ethene.
${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{{\mathrm{H}}^{+}/{\mathrm{H}}_2\mathrm{O}}{\to }{\mathrm{CH}}_2={\mathrm{CH}}_2$