Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

As shown, chlorine gas reacts with iron(II) ions in aqueous solution. $\text{Cl}_2(g) + 2\text{Fe}^{2+}(aq) \rightarrow 2\text{Cl}^-(aq) + 2\text{Fe}^{3+}(aq)$
(a(i))[4]

Complete and label the diagram to show how the standard cell potential, $E^\circ_{\text{cell}}$, for the reaction above can be measured under standard conditions.

(a(ii))[1]

Calculate the $E^\circ_{\text{cell}}$ for this reaction using the Data Booklet.

(b)[1]

What colour change would you observe when chlorine gas is bubbled through a solution containing $\text{Fe}^{2+}(aq)$ ions until the reaction is complete?

(c)[2]

Predict the effect, if any, of decreasing the concentration of $\text{Cl}^-(aq)$ on the size of the cell potential in a(i). Explain your answer.

(d(i))[2]

A fuel cell is an electrochemical cell used to generate electrical energy. In the alkaline hydrogen-oxygen fuel cell, $\text{H}_2(g)$ and $\text{O}_2(g)$ are supplied to two inert electrodes dipped in an alkaline solution. Write the half-equations for the reactions occurring at each of these electrodes. Hydrogen electrode ................. Oxygen electrode .................

(d(ii))[1]

Construct the equation for the overall reaction.

(d(iii))[1]

Suggest one possible advantage of a hydrogen-oxygen fuel cell compared with a conventional ‘simple cell’ battery.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Fe$^{2+}$/Fe$^{3+}$ and Cl$^-$/Cl$_2$ half-cells fitted with Pt electrodes

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