Question

(a) How is ethanoic acid obtained from ethanol? Write down the chemical equation of the reaction involved.
(b) How would you distinguish between ethanol and ethanoic acid by chemical test?
(c) Explain the formation of scum when hard water is treated with soap.

Answer 1

(a) When ethanol (ethyl alcohol) is heated in the presence of alkaline potassium permanganate solution or acidified potassium dichromate solution, it gets oxidised to ethanoic acid. This reaction is known as oxidation reaction.

The chemical equation for the above reaction is:
${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}+2\left[\mathrm{O}\right]\underset{\mathrm{or}\mathrm{acidified}\mathrm{K}2\mathrm{Cr}2\mathrm{O}7}{\overset{\mathrm{alkaline}\mathrm{KMnO}4,\mathrm{Heat}}{\to }}{\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{H}}_2\mathrm{O}$

(b) Ethanoic acid releases carbon dioxide gas on reacting with sodium bicarbonate. It is represented by the following equation:
${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{NaHCO}}_3\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

On the other hand, ethanol does not give out a brisk effervescence (carbon dioxide) with sodium bicarbonate.

(c) Scum is formed when a soap is used in hard water. This happens because a large amount of soap is utilised in reacting with the magnesium and calcium ions of hard water. An insoluble curdy precipitate, scum, sticks to the clothes making them difficult to be cleaned.