Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

(a)[2]

What is meant by the term standard electrode potential, SEP?

(b)[5]

Draw a fully labelled diagram of the apparatus that could be used to measure the SEP of the $\text{Fe}^{3+}/\text{Fe}^{2+}$ electrode.

(c)

The reaction between $\text{Fe}^{3+}$ ions and $\text{I}^-$ ions is an equilibrium reaction: $2\text{Fe}^{3+}(aq) + 2\text{I}^-(aq) \rightleftharpoons 2\text{Fe}^{2+}(aq) + \text{I}_2(aq)$.

(c(i))

Use the Data Booklet to work out the $E^\circ_{cell}$ for this reaction.

(c(ii))

Hence state, with a reason, whether there will be more products or more reactants at equilibrium.

(c(iii))

Write the expression for $K_c$ for this reaction, and state its units.

(c(iv))

An experiment used solutions of $\text{Fe}^{3+}(aq)$ and $\text{I}^-(aq)$ that had the same concentration. $100\,\text{cm}^3$ of each solution were combined and left until equilibrium was reached. The equilibrium concentrations of $\text{Fe}^{3+}(aq)$ and $\text{I}_2(aq)$ were: $[\text{Fe}^{3+}(aq)] = 2.0 \times 10^{-4}\,\text{mol dm}^{-3}$, $[\text{I}_2(aq)] = 1.0 \times 10^{-2}\,\text{mol dm}^{-3}$. Use these data, together with the equation given in (c), to calculate the concentrations of $\text{Fe}^{2+}(aq)$ and $I^-(aq)$ at equilibrium.

(c(v))[8]

Calculate the $K_c$ for this reaction.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: The potential of an electrode when compared with a standard hydrogen electrode (SHE), or the EMF of a cell made up of the test electrode and the SHE

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