Describe what happens when an alkene reacts with bromine water. What observation can be made during this reaction?

When an alkene reacts with bromine water, the bromine adds across the double bond, resulting in the formation of a dibromoalkane. The observation during this reaction is that the bromine water, which is initially orange-brown, becomes decolorised.

This question evaluates the student's ability to describe a specific reaction involving alkenes and to identify observable changes, reinforcing their understanding of addition reactions and the properties of alkenes. This response is aligned to Reactions of alkenes because it explains describe the reactions and conditions for the addition of hydrogen, water and halogens to alkenes using the correct AQA GCSE Chemistry organic context. Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.