Reactivity 3.2—Electron transfer reactions: Practice Questions

In the following reaction, which species is being oxidized?

\( 2\text{Al}(s) + 3\text{Fe}^{2+}(aq) \rightarrow 2\text{Al}^{3+}(aq) + 3\text{Fe}(s) \)

Consider the following standard reduction potentials:
\( \text{Zn}^{2+}(aq) + 2e^- \rightleftharpoons \text{Zn}(s) \text{ } E^\theta = -0.76 \text{ V} \)
\( \text{Ag}^+(aq) + e^- \rightleftharpoons \text{Ag}(s) \text{ } E^\theta = +0.80 \text{ V} \)

What is the standard cell potential, \( E^\theta_{\text{cell}} \), for a voltaic cell constructed using these two half-cells?

What is the product formed at the cathode during the electrolysis of aqueous sodium sulfate, \( \text{Na}_2\text{SO}_4(aq) \), using inert electrodes?

What is the oxidation number of chromium in the dichromate ion, \( \text{Cr}_2\text{O}_7^{2-} \)?

In a voltaic cell, which statement correctly describes the flow of electrons and the process at the cathode?

Determine the average oxidation state of sulfur in the tetrathionate ion, \(S_4O_6^{2-}\), and identify which species is the oxidizing agent in the reaction: \(2S_2O_3^{2-}(aq) + I_2(aq) \rightarrow S_4O_6^{2-}(aq) + 2I^-(aq)\).

An unknown metal ion \(M^{n+}\) is reduced to the metal at the cathode. If 0.020 moles of electrons produce 0.486 g of Magnesium (Ar = 24.31), deduce the value of \(n\).

State the relationship between the standard electrode potential (\(E^\theta\)) of a metal and its strength as a reducing agent, and explain why potassium has a very negative \(E^\theta\) value.

A student performs a redox titration to determine the concentration of iron(II) ions in a solution. A 25.00 \(cm^3\) sample of the iron(II) solution was acidified and titrated against a 0.0200 \(mol\ dm^{-3}\) solution of potassium manganate(VII), \(KMnO_4\). The average titre was found to be 18.50 \(cm^3\).

(a) State the balanced ionic equation for the reaction between \(Fe^{2+}\) and \(MnO_4^-\) in acidic solution.
(b) Calculate the concentration of the \(Fe^{2+}\) ions in the original solution in \(mol\ dm^{-3}\).
(c) Explain why the titration is carried out in acidic conditions and identify the indicator used for this titration.

Consider the Standard Hydrogen Electrode (SHE).

(a) Describe the components and the conditions required for the Standard Hydrogen Electrode to operate at standard state.
(b) A voltaic cell is set up by connecting a SHE to a \(Ni^{2+}(aq)/Ni(s)\) half-cell. If the voltmeter reads 0.25 V and the SHE acts as the cathode, determine the standard electrode potential of the nickel half-cell.
(c) Explain why platinum is used as the electrode in the SHE and why the surface is often coated with "platinum black".