What happens when an alkane mixes with bromine water?

Bromine water does not react with alkanes under standard conditions. Bromine water is used to tell the difference between alkanes and alkenes, as it reacts with alkenes to produce a brominated hydrocarbon and to turn the bromine water from yellow-brown to colorless.

Alkanes react with bromine water if ultraviolet light is present. In this case, they produce a brominated hydrocarbon with hydrogen bromide. If the alkane in question has more than two carbon atoms, a variety of compounds is formed. Alkynes, hydrocarbons with at least one carbon-carbon triple bond, also undergo bromination, so this method cannot be used to determine the difference between them and alkenes.