9.4 Distinguishing saturated and unsaturated hydrocarbons

9.4 Distinguishing saturated and unsaturated hydrocarbons

To distinguish between saturated and unsaturated hydrocarbons, you can perform the bromine water test. This test involves adding bromine water (Br in water, which is an orange- brown solution) to the hydrocarbon and observing the colour change.

Procedure

Observations

Saturated hydrocarbons (alkanes) will not react with bromine water. The solution will remain orange- brown. Unsaturated hydrocarbons (alkenes and alkynes) will react with bromine water. The solution will decolourize (turn colourless) because the bromine reacts with the double or triple bonds.

Symbol Equations

For an alkene (unsaturated hydrocarbon)

Ethene reacts with bromine to form dibromoethane.

Ethene (colourless) (Reddish- brown) 1,2- Dibromo ethane (colourless)

Ethyne reacts with bromine to form tetrabromoethane.)