Displacement reactions as redox reactions
4 marks · NormalThe table shows observations from adding different halogen solutions to various potassium halide solutions:
| Halogen solution | Potassium halide solution | Observation |
|---|---|---|
| Chlorine | Potassium iodide | Brown solution formed |
| Bromine | Potassium chloride | No change |
| Iodine | Potassium bromide | No change |
| Chlorine | Potassium bromide | Orange solution formed |
Identify which pairs in the table show a displacement reaction.
For one of the pairs that show a displacement, write the ionic equation for the reaction.
Explain why no change is observed in the reaction between bromine and potassium chloride.
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
(a) Chlorine with potassium iodide and chlorine with potassium bromide · must show Both displacement reactions identified
(b) · must show Ionic equation, correct species and state symbols
(c) Bromine is less reactive than chlorine and cannot displace chloride ions. · must show Reference to bromine’s reactivity and inability to displace chloride
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies both pairs where a new colour appears as displacement reactions.
M1 (b) · 1 mark · Writes correct ionic equation for one pair: or
A1 (b) · 1 mark · All correct state symbols.
B2 (c) · 1 mark · Correct explanation that bromine cannot displace chloride ions because it is less reactive than chlorine.
Worked solution
a) Displacement reactions occur where there is a colour change: chlorine with potassium bromide and chlorine with potassium iodide.
b) For chlorine and potassium bromide: 2Br−(aq) + Cl2(aq) → 2Cl−(aq) + Br2(aq)
c) Bromine cannot displace chloride ions from potassium chloride because it is less reactive than chlorine.