Question

An Al/Al3+ concentration cell is constructed where both electrodes are aluminum. The Al3+ concentrations in the electrolyte are 0.4M for half cell A and 0.02M for half cell B and the operation temperature is +10 C.

Write reactions for each half cell.

Answer 1

An Al/Al3+ concentration cell involves the reduction reaction, Al3+ (aq) + 3e- → Al (s), at the cathode of half-cell A and the oxidation reaction, Al (s) → Al3+ (aq) + 3e-, at the anode of half-cell B.

Step-by-step explanation:

The student is asking about the reactions at each half-cell of an aluminum concentration cell at +10°C with different concentrations of Al3+ ions in the electrolyte. For half-cell A with a concentration of 0.4M Al3+, the reaction would be:

• Al3+ (aq) + 3e- → Al (s) at the cathode (reduction)

For half-cell B with a concentration of 0.02M Al3+, the reaction is:

• Al (s) → Al3+ (aq) + 3e- at the anode (oxidation)

In the concentration cell, the aluminum metal is electrolysis at the cathode, where the Al3+ ions gain electrons to form solid aluminum. Over time, as the cell operates, the concentration of Al3+ ions in half-cell A will decrease while it will increase in half-cell B until equilibrium is reached.