1:59 (Triple only) write ionic half-equations representing the reactions at the electrodes during electrolysis and understand why these reactions are classified as oxidation or reduction

Oxidation: the loss of electrons or the gain of oxygen

Reduction: the gain of electrons or the loss of oxygen

 

Example: The electrolysis of lead (II) bromide, PbBr2

At the cathode (negative electrode):   Pb2+ (l) + 2e–  →  Pb (l)         (reduction)

At the anode (positive electrode):       2Br– (l)      →  Br2 (g) + 2e–       (oxidation)

 

Example: The electrolysis of aluminium oxide, Al2O3

At the cathode:   Al3+ + 3e–    →    Al         (reduction)

At the anode:      2O2-    →    O2 + 4e–       (oxidation)

 

Example: The electrolysis of sodium chloride solution (NaCl (aq))

At the cathode:   2H+ (aq) + 2e–  →  H2 (g)       (reduction)

At the anode:      2Cl– (aq)    →  Cl2 (g) + 2e–       (oxidation)

 

Example: The electrolysis of copper sulfate solution (CuSO4 (aq))

At the cathode:   Cu2+ (aq) + 2e–  →  Cu (s)      (reduction)

At the anode:      4OH– (aq)     →  O2 (g) + 2H2O (l) + 4e–       (oxidation)