Chemistry 9701 · AS & A Level · 9.1

9.1 — practice question

A Daniell cell is an electrochemical cell made up of a $\text{Cu}^{2+}(\text{aq})/\text{Cu}(\text{s})$ electrode together with a $\text{Zn}^{2+}(\text{aq})/\text{Zn}(\text{s})$ electrode.
(a)[2]

Define standard cell potential, $E^\ominus_{\text{cell}}$. State the standard conditions in your response.

(b(i))[3]

Draw a labelled diagram of this electrochemical cell. Include all necessary substances and the relevant apparatus required to measure the $E^\ominus_{\text{cell}}$. It is not necessary to state the conditions used.

(b(ii))[1]

State the charge carriers that transfer current through the solutions and through the wire. The solutions __________ The wire __________

(b(iii))[2]

The standard electrode potential, $E^\ominus$, for the $\text{Zn}^{2+}(\text{aq})/\text{Zn}(\text{s})$ electrode is $-0.76\text{ V}$. Water is added to a standard $\text{Zn}^{2+}(\text{aq})/\text{Zn}(\text{s})$ electrode. The new concentration of $\text{Zn}^{2+}(\text{aq})$ becomes $0.25\text{ mol dm}^{-3}$. Use the Nernst equation to work out the electrode potential, $E$, for this updated $\text{Zn}^{2+}(\text{aq})/\text{Zn}(\text{s})$ electrode.

(c(i))[1]

An electrochemical cell has a $\text{ZnO}/\text{Zn}$ electrode and a $\text{MnO}_2/\text{Mn}_2\text{O}_3$ electrode in an alkaline electrolyte. The standard cell potential, $E^\circ_{\text{cell}}$, for this cell is $+1.47\,\text{V}$. The half-equation at each electrode when this cell is discharging is shown. $\text{Zn} + 2\text{OH}^- \rightarrow \text{ZnO} + \text{H}_2\text{O} + 2e^-$ $2\text{MnO}_2 + \text{H}_2\text{O} + 2e^- \rightarrow \text{Mn}_2\text{O}_3 + 2\text{OH}^-$ Use this information to determine the change in oxidation state of manganese when this cell is discharging. from ........................ to ........................

(c(ii))[1]

Write the equation for the overall reaction that occurs when this cell is discharging.

(c(iii))[1]

The $E^\circ$ for the $\text{ZnO}/\text{Zn}$ electrode is $-1.28\,\text{V}$. Calculate the standard electrode potential, $E^\circ$, for the $\text{MnO}_2/\text{Mn}_2\text{O}_3$ electrode.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: potential difference / voltage / EMF AND across the two half-cells / the two electrodes in a cell

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