Displacement reactions involving the halogens
3 marks · NormalExplain why chlorine can displace bromine from potassium bromide solution, but bromine cannot displace chlorine from potassium chloride solution. In your answer, refer to the reactivity trend of halogens.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Also accept: May use the term 'higher tendency to gain electrons' as a supporting point
Common mistakes: Misidentifying the trend (thinking reactivity increases down the group); Not referring to position in the group
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States that halogen reactivity decreases down the group.
M2 · 1 mark · States that a more reactive halogen displaces a less reactive halide from solution.
A1 · 1 mark · Correctly applies this to chlorine/bromine: chlorine is above bromine, so it can displace bromine.
Worked solution
Halogen reactivity decreases as you go down group 7. Chlorine is above bromine in the group, so it is more reactive and can displace bromine from potassium bromide solution. Bromine cannot displace chlorine from potassium chloride, because it is less reactive than chlorine.