Question

Give a chemical test to distinguish between:
(a) saturated and unsaturated compounds
(b) ethane and ethene
(c) ethene (ethylene) and ethyne (acetylene).

[3 MARKS]

Answer 1

Each Part: 1 Mark

(a) Add a few drops of alkaline $KMn{O}_4$ solution to the organic compound. If the purple colour of $KMn{O}_4$ doesn not fade, then the given organic compound is saturated and if the purple colour of $KMn{O}_4$ fades, then the given organic compound is unsaturated.

(b) To distinguish between ethane and ethene: Add a few drops of alkaline potassium permanganate $KMn{O}_4$ solution to the given hydrocarbons. The hydrocarbon in which no change in colour is observed is ethane and the hydrocarbon which purple colour of $KMn{O}_4$ fades is ethene.

(c) To distinguish between ethene and ethyne: Add a few drops of ammonical cuprous chloride to each of ethylene (ethene) and acetylene (ethyne). No change will be observed in the case of ethylene (ethene) but in the case of acetylene (ethyne), red precipitate of copper acetylide is formed.