Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

(a)[2]

What does the term standard electrode potential, SEP, mean?

(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 of $\text{Fe}^{3+}$ ions with $\text{I}^-$ ions is an equilibrium reaction.

(c(i))

Using the Data Booklet, Calculate the $E^{\theta}_{\text{cell}}$ for this reaction: $2\text{Fe}^{3+}\text{(aq)} + 2\text{I}^-\text{(aq)} \rightleftharpoons 2\text{Fe}^{2+}\text{(aq)} + \text{I}_2\text{(aq)}$.

(c(ii))

Hence state, with a reason, whether equilibrium will contain more products or more reactants.

(c(iii))

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

(c(iv))

Use these data, together with the equation given in (c), to work out the equilibrium concentrations of $\text{Fe}^{2+}\text{(aq)}$ and $\text{I}^-\text{(aq)}$. The equilibrium concentrations were $[\text{Fe}^{3+}\text{(aq)}] = 2.0 \times 10^{-4}\ \text{mol dm}^{-3}$ and $[\text{I}_2\text{(aq)}] = 1.0 \times 10^{-2}\ \text{mol dm}^{-3}$.

(c(v))[8]

Calculate the $K_c$ value 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: Potential of an electrode measured against a standard hydrogen electrode (SHE), or the EMF of a cell made from the test electrode and the SHE

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