Question 12 – Electrode potentials and electrochemical cells (A-level only) - Questions

A standard hydrogen electrode acts as the primary reference for measuring electrode potentials.

State the substances, their concentrations (where applicable), and the conditions needed to set up a standard hydrogen electrode.

A student sets up an electrochemical cell to measure the standard electrode potential for the $VO2+(aq)/V(s)\text{VO}^{2+}(\text{aq})/\text{V}(\text{s})$ electrode using a standard $Cu2+(aq)/Cu(s)\text{Cu}^{2+}(\text{aq})/\text{Cu}(\text{s})$ electrode ( $VE^\theta = +0.34\text{ V}$ ) as a secondary reference standard.

To make $cm3250\text{ cm}^3$ of a standard solution containing $dm−31.0\text{ mol dm}^{-3}$ acidified $VO2+(aq)\text{VO}^{2+}(\text{aq})$ , the student dissolves solid vanadyl sulfate ( $VOSO4\text{VOSO}_4$ , $M_r = 163.0$ ) in $dm−30.50\text{ mol dm}^{-3}$ sulfuric acid.

Describe the experiment to find the standard electrode potential for the $VO2+(aq)/V(s)\text{VO}^{2+}(\text{aq})/\text{V}(\text{s})$ electrode. Your response should include details of:

How to prepare the $cm3250\text{ cm}^3$ solution of acidified $VO2+(aq)\text{VO}^{2+}(\text{aq})$ (including the calculation of the mass of solid needed).
How to set up and connect the half-cells.
How a voltmeter reading of $V1.14\text{ V}$ (with the copper electrode connected to the positive terminal) is used to find the standard electrode potential of the $VO2+(aq)/V(s)\text{VO}^{2+}(\text{aq})/\text{V}(\text{s})$ electrode.

Give the half-equation for the electrode reaction occurring at the $VO2+(aq)/V(s)\text{VO}^{2+}(\text{aq})/\text{V}(\text{s})$ electrode under acidic conditions.