Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.
Solution
Chemical test:- Bromine water test, if unsaturated hydrocarbons are added to it then the solution turns colourless. The unsaturated hydrocarbon decolourise bromine water. Whereas no change takes place to the solution when saturated hydrocarbons are added to bromine water.
Physical test:- Distinction between saturated and unsaturated hydrocarbons: Saturated hydrocarbons burn in the air with clear (blue) flame, whereas burning of unsaturated hydrocarbons (alkenes and alkynes) gives sooty (yellowish) flame. Saturated hydrocarbons contain less percentage of carbon as compared to unsaturated hydrocarbons; therefore, they get completely oxidised by the oxygen present in the air on burning. Unsaturated hydrocarbons require lot of oxygen for complete oxidation whose demand is not fulfilled by air. Due to this reason, unsaturated hydrocarbons burn with a sooty flame. The sooty flame contains partially burnt carbon in the form of soot.
