The electrochemical cell represented by the cell notation below is used to investigate the relationship between the concentration of $X^{2+}(aq)$ and the emf of the cell - NSC Physical Sciences - Question 8 - 2017 - Paper 2

A voltmeter or multimeter is required to measure the emf of the cell.

The salt bridge ensures electrical neutrality within the electrochemical cell.

The standard conditions required are:

• Temperature: 25 °C or 298 K
• Concentration: 1 mol·dm⁻³ for all ionic species.

The graph indicates that the emf increases as the concentration of the oxidizing agent, $X^{2+}(aq)$, increases. This relationship shows that the emf is directly proportional to the concentration of $X^{2+}(aq)$.

To identify electrode X, we can utilize the Nernst equation:

E = E^{ ext{o}} - rac{RT}{nF} ext{ln} rac{[X^{2+}]}{[Zn^{2+}]}

Given E^{ ext{o}} (standard electrode potential) values and measurements from the graph, we can solve for the concentration when the emf reaches certain values. Based on the values, we determine that $X$ corresponds to Copper (Cu), where the half-reaction at the cathode is: [ Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) ]

The overall cell reaction can be summarized as follows:

$Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$

This reflects the transfer of electrons from zinc to copper ions.