Describe the test which differentiates alkanes from alkenes

The test for telling the difference between a saturated alkane and unsaturated alkene involves adding bromine water, which is brown in colour - the unsaturated alkene has a double bond and can react with the bromine, causing a colour change to colourless. As alkanes do not have a double bond, they are unable to react with the bromine and hence the brown colouration will persist.