Displacement reactions as redox reactions
4 marks · NormalTwo students discuss the reaction between chlorine and potassium iodide solution.
Write the ionic equation for this reaction, including state symbols.
Explain, using the meanings of oxidation and reduction, which substance is oxidised and which is reduced in this reaction.
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(a) · must show Ionic species, correct state symbols, balanced equation
(b) Iodide ions are oxidised (lose electrons) to form iodine; chlorine is reduced (gains electrons) to form chloride ions. Oxidation is loss of electrons; reduction is gain of electrons. · must show Correct identification of oxidised and reduced substances, electron transfer, definitions
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Marking points
M1 (a) · 1 mark · Correct reactants and products written as ions and molecules.
A1 (a) · 1 mark · All state symbols correct and present.
M2 (b) · 1 mark · States iodide ions are oxidised (lose electrons) and chlorine is reduced (gains electrons).
A2 (b) · 1 mark · Defines oxidation as loss and reduction as gain of electrons, or equivalent explanation.
Worked solution
a) The ionic equation is:
b) The iodide ions, I−, are oxidised because they lose electrons to become I2. Chlorine, Cl2, is reduced because it gains electrons to become Cl−. Oxidation is loss of electrons, and reduction is gain of electrons.