Inorganic Chemistry
8 marks · NormalThis question is about electronically explaining group reactivity and redox displacement.
Explain why potassium is more reactive than sodium, referring to electronic structure.
The reaction between chlorine and iodide ions is a redox displacement. Write the ionic equation for this reaction and state which substance is oxidised and which is reduced.
Using electronic configurations, explain why chlorine is able to displace iodine from a solution of potassium iodide.
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(a) Potassium has more electron shells than sodium. Its outer electron is further from the nucleus, experiences weaker nuclear attraction, and is lost more easily, making potassium more reactive. · must show More shells, Weaker attraction, Easier to lose electron
(b) 2I^-(aq) + Cl2(aq) → 2Cl^-(aq) + I2(aq); Iodide ions are oxidised to iodine; chlorine is reduced to chloride ions. · must show Correct ionic equation, States I^- oxidised, States Cl2 reduced
(c) Chlorine can gain an electron more easily because its atoms are smaller and the added electron is closer to the nucleus, so chlorine is more reactive and displaces iodine. · must show Smaller atom, Added electron closer to nucleus, Stronger attraction for electrons
Common mistakes: Mixing up oxidation/reduction; Not stating electronic shell reason for reactivity
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Marking points
M1 (a) · 1 mark · Mentions potassium has more electron shells than sodium
M2 (a) · 1 mark · States outer electron is further from nucleus or weaker attraction
A1 (a) · 1 mark · Concludes potassium loses electron more easily, so is more reactive
M3 (b) · 1 mark · Correct ionic equation written
A2 (b) · 1 mark · Correctly identifies I^- as oxidised
A3 (b) · 1 mark · Correctly identifies Cl2 as reduced
M4 (c) · 1 mark · Chlorine is smaller/higher electron attraction than iodine
A4 (c) · 1 mark · Chlorine gains electron more easily or explains why displacement occurs
Worked solution
a. Potassium has more electron shells than sodium, so its outer electron is further from the nucleus and is held less tightly. This makes it easier to lose the outer electron and therefore potassium is more reactive than sodium.
b. The ionic equation is 2I^-(aq) + Cl2(aq) → 2Cl^-(aq) + I2(aq). Iodide ions lose electrons and are oxidised to iodine; chlorine gains electrons and is reduced to chloride ions.
c. Chlorine is smaller than iodine. Its atoms gain electrons more easily because the added electron is closer to the nucleus and more strongly attracted, so chlorine is more reactive and can displace iodine from a solution.