Displacement reactions can be used to determine the relative reactivity of the halogen elements

This demonstration by Nigel Baldwin on YouTube shows the reactions between chlorine, bromine and iodine ions with potassium chloride, potassium bromide and potassium iodide respectively. You will see a colour change where a reaction has occurred. The reactivity trend of these three halogens can be deduced from the reactions that take place.

Mr Baldwin has produced clear colour changes for the purposes of filming by using higher concentrations of solutions than would be appropriate in the classroom. If students are going to carry this practical out in a school laboratory then CLEAPSS suggests that 0.002M bromine water is suitable for halogen/halide displacements. Solutions should also be decanted into smaller bottles for better handling to avoid spillages.

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