Electrochemistry (A Level only): Practice Questions

What is the oxidation state of sulfur in the thiosulfate ion, \(S_2O_3^{2-}\)?

A current of \(2.50\text{ A}\) is passed through an aqueous solution of copper(II) sulfate, \(CuSO_4\), for \(30.0\text{ minutes}\).
What mass of copper is deposited at the cathode?
(Faraday constant, \(F = 9.65 \times 10^4\text{ C mol}^{-1}\); \(A_r(Cu) = 63.5\))

A student carries out the electrolysis of aqueous sodium sulfate using a constant current of \(0.500 \text{ A}\) for \(30.0 \text{ minutes}\). What is the total volume of gas, measured at room temperature and pressure (r.t.p.), produced at the anode?
(Faraday constant \(F = 96500 \text{ C mol}^{-1}\); molar volume of gas at r.t.p. \(= 24.0 \text{ dm}^3 \text{ mol}^{-1}\))

What quantity of electric charge, in coulombs, is carried by \(0.20\text{ mol}\) of electrons?
(Faraday constant, \(F = 9.65 \times 10^4\text{ C mol}^{-1}\))

Using the standard electrode potentials provided, which statement regarding the feasibility of the reactions listed below is correct?

\(Fe^{3+}(aq) + e^{-} \rightleftharpoons Fe^{2+}(aq) \quad E^{\ominus} = +0.77 \text{ V}\)
\(Cl_{2}(g) + 2e^{-} \rightleftharpoons 2Cl^{-}(aq) \quad E^{\ominus} = +1.36 \text{ V}\)
\(Br_{2}(l) + 2e^{-} \rightleftharpoons 2Br^{-}(aq) \quad E^{\ominus} = +1.07 \text{ V}\)
\(I_{2}(s) + 2e^{-} \rightleftharpoons 2I^{-}(aq) \quad E^{\ominus} = +0.54 \text{ V}\)

(a) Define the term standard electrode (reduction) potential, $E^{\ominus}$. State the standard conditions required for its measurement.

(b) A standard electrochemical cell is set up using the standard hydrogen electrode (SHE) as a reference. Describe the construction of the standard hydrogen electrode, outlining the components and the role of platinum.

(c) Given the following standard electrode potentials:

Use these values to predict whether cadmium metal, $\text{Cd}(\text{s})$, can reduce $\text{Ag}^+(\text{aq})$ ions under standard conditions. Justify your answer.

Use the following standard electrode potentials ($E^{\ominus}$) to answer the questions below:

(a) Determine the standard cell potential, $E_{\text{cell}}^{\ominus}$, for the spontaneous reaction that occurs when these two standard half-cells are connected.

(b) Write the overall balanced ionic equation for the spontaneous reaction.

(c) Identify the species that acts as the strongest reducing agent and the species that acts as the strongest oxidising agent in this overall reaction.

(d) Calculate the standard Gibbs Free Energy change, $\Delta G^{\ominus}$, for this spontaneous reaction in $\text{kJ mol}^{-1}$ at $298 \text{ K}$.
($F = 96500 \text{ C mol}^{-1}$)