Storage cells and fuel cells are types of electrochemical cells.
The standard electrode potentials for five redox systems are shown in the table below:
| Redox system | Half-equation | Eθ/VE^\theta / \text{V}Eθ/V |
|---|---|---|
| 1 | Fe2+(aq)+2e−⇌Fe(s)\text{Fe}^{2+}(\text{aq}) + 2\text{e}^- \rightleftharpoons \text{Fe}(\text{s})Fe2+(aq)+2e−⇌Fe(s) | −0.44-0.44−0.44 |
| 2 | O2(g)+2H2O(l)+4e−⇌4OH−(aq)\text{O}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l}) + 4\text{e}^- \rightleftharpoons 4\text{OH}^-(\text{aq})O2(g)+2H2O(l)+4e−⇌4OH−(aq) | +0.40+0.40+0.40 |
| 3 | Cu2+(aq)+e−⇌Cu+(aq)\text{Cu}^{2+}(\text{aq}) + \text{e}^- \rightleftharpoons \text{Cu}^+(\text{aq})Cu2+(aq)+e−⇌Cu+(aq) | +0.15+0.15+0.15 |
| 4 | Cu+(aq)+e−⇌Cu(s)\text{Cu}^+(\text{aq}) + \text{e}^- \rightleftharpoons \text{Cu}(\text{s})Cu+(aq)+e−⇌Cu(s) | +0.52+0.52+0.52 |
| 5 | VO2+(aq)+2H+(aq)+e−⇌VO2+(aq)+H2O(l)\text{VO}_2^+(\text{aq}) + 2\text{H}^+(\text{aq}) + \text{e}^- \rightleftharpoons \text{VO}^{2+}(\text{aq}) + \text{H}_2\text{O}(\text{l})VO2+(aq)+2H+(aq)+e−⇌VO2+(aq)+H2O(l) | +1.00+1.00+1.00 |
A student sets up an electrochemical cell based on redox systems 1 and 5.
Describe the key components of a labelled diagram showing how this cell could be set up in the laboratory.
Construct the equation for the overall cell reaction.
Copper(I) ions, Cu+(aq)\text{Cu}^+(\text{aq})Cu+(aq), undergo disproportionation in solution to form copper metal, Cu(s)\text{Cu}(\text{s})Cu(s), and copper(II) ions, Cu2+(aq)\text{Cu}^{2+}(\text{aq})Cu2+(aq).
Explain, in terms of oxidation numbers, why disproportionation has taken place.
Explain, in terms of electrode potentials and equilibrium shifts, why Cu+(aq)\text{Cu}^+(\text{aq})Cu+(aq) disproportionates. Use the information in the table.
An alkaline hydrogen-oxygen fuel cell is set up.
The overall equation for the cell reaction is:
2H2(g)+O2(g)→2H2O(l) 2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{H}_2\text{O}(\text{l}) 2H2(g)+O2(g)→2H2O(l)Redox system 2 in the table is the positive electrode of this cell.
Write the half-equation at the negative electrode.
The overall cell potential is 1.23 V1.23\text{ V}1.23 V. Calculate the standard electrode potential of the negative electrode.
State one important feature of a fuel cell that is different from a conventional storage cell.
