Question

How do we use bromine water to distinguish between saturated hydrocarbons, unsaturated hydrocarbons, and phenols?

Answer 1

Bromine Water test:

• Saturated hydrocarbons are those compounds in which all Carbons are attached to each other by a single bond. E.g. Methane, Ethane, etc.
• Unsaturated hydrocarbons are those compounds in which Carbons are attached to each other by a double bond. E.g. Ethene, Propene, etc.
• Phenol is an aromatic compound in which the Hydroxy group($-\mathrm{OH}$) is attached to the Benzene ring.
• The test used to distinguish between them is the Bromine water test.
• Bromine dissolved in the water is called Bromine water. It is a reddish-brown-coloured solution.
• If Bromine water is added to the solution of saturated compounds like alkanes, the reaction mixture is not decolourized.

$\mathrm{Saturated}\mathrm{hydrocarbon}+\mathrm{Bromine}\mathrm{water}\to \mathrm{No}\mathrm{change}\mathrm{in}\mathrm{color}\mathrm{of}\mathrm{solution}$

• If bromine water is mixed with unsaturated hydrocarbons like alkenes, the mixture is decolourized.

$\mathrm{Unsaturated}\mathrm{hydrocarbon}+\mathrm{Bromine}\mathrm{water}\to \mathrm{Decolorization}$

• If Phenol and Bromine water are mixed together, then white-coloured precipitate is present along with decolourization of the reaction mixture.

$\mathrm{Phenol}+\mathrm{Bromine}\mathrm{water}\to \mathrm{White}\mathrm{precipitate}$

Hence, the Bromine-water test is used to distinguish saturated hydrocarbons, unsaturated hydrocarbons, and Phenols.