Reactions of the halogens
4 marks · NormalThe halogens react with metals and can also displace each other from solutions of their salts.
State what is meant by a displacement reaction involving the halogens.
Write a word equation for the reaction between bromine and potassium iodide solution.
Explain why chlorine can displace bromine from sodium bromide solution, but iodine cannot.
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(a) A more reactive halogen replaces a less reactive halogen from its compound. · must show States requirement of more reactive halogen replacing less reactive halogen from salt/solution
(b) Bromine + potassium iodide 3e potassium bromide + iodine · must show Correct formation of potassium bromide and iodine
(c) Chlorine is more reactive than bromine, so it can displace bromine from sodium bromide solution. Iodine is less reactive than bromine, so it cannot displace bromine. · must show Chlorine more reactive than bromine; iodine less reactive than bromine; explanation of displacement ability
Common mistakes: Wrong order of reactivity; Mixing up halide ions and halogens
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Marking points
B1 (a) · 1 mark · Correct definition of halogen displacement reaction (must mention more reactive replacing less reactive)
B2 (b) · 1 mark · Correct word equation: bromine + potassium iodide 3e potassium bromide + iodine
B3 (c) · 1 mark · Chlorine is more reactive than bromine, so can displace bromine (or equivalent statement for first mark)
B4 (c) · 1 mark · Iodine is less reactive than bromine, so cannot displace bromine (or equivalent statement for second mark)
Worked solution
a) A displacement reaction is when a more reactive halogen replaces a less reactive halogen from a compound (usually a solution of its salt).
b) bromine + potassium iodide 3e potassium bromide + iodine
c) Chlorine is more reactive than bromine, so chlorine can displace bromine from sodium bromide solution. Iodine is less reactive than bromine, so it cannot displace bromine.