CAIE A Level Chemistry 9701 · Electrochemistry

Electrochemistry: describe question

Describe7 marksChallenge

Standard electrode potentials for three half-reactions are given.

FeX3+(aq)+eX−⇌FeX2+(aq)\ce{Fe^{3+}(aq) + e^- <=> Fe^{2+}(aq)} E∘=+0.77E^\circ = +0.77 V

IX2(s)+2 eX−⇌2 IX−(aq)\ce{I2(s) + 2e^- <=> 2I^-(aq)} E∘=+0.54E^\circ = +0.54 V

CeX4+(aq)+eX−⇌CeX3+(aq)\ce{Ce^{4+}(aq) + e^- <=> Ce^{3+}(aq)} E∘=+1.44E^\circ = +1.44 V

(a) Define the terms standard electrode potential and standard cell potential.

(b) Describe the standard hydrogen electrode and how it can be used to measure the standard electrode potential of the FeX3+/FeX2+\ce{Fe^{3+}/Fe^{2+}} half-cell.

(c) When a cell is constructed by connecting the FeX3+/FeX2+\ce{Fe^{3+}/Fe^{2+}} half-cell and the IX2/IX−\ce{I2/I^-} half-cell, deduce the polarity of each electrode and state the direction of electron flow in the external circuit.

(d) Construct the overall redox equation for the reaction that occurs in the cell in (c).

(e) Predict whether CeX4+(aq)\ce{Ce^{4+}(aq)} ions can oxidise IX−(aq)\ce{I^- (aq)} ions under standard conditions. Use the data to justify your answer and state which is the stronger oxidising agent.

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