Predict the product formed at the negative electrode during the electrolysis of sodium chloride solution.
Hydrogen will be produced because sodium is more reactive than hydrogen.
Predict the product formed at the negative electrode during the electrolysis of copper chloride solution.
Copper will be produced because copper is less reactive than hydrogen.
Oxygen is produced (from hydroxide ions) at the anode, unless halide ions (chloride, bromide or iodide ions) are present. In that case, the negatively charged halide ions lose electrons and form the corresponding halogen (chlorine, bromine or iodine).
The balanced half equation (higher tier only) for the formation of oxygen from hydroxide ions is:
4OH- → 2H2O + O2 + 4e-
The table summarises the product formed at the anode during the electrolysis of different electrolytes in solution.
|Negative ion from electrolyte||Element given off at anode|
|Chloride, Cl-||Chlorine, Cl2|
|Bromide, Br-||Bromine, Br2|
|Iodide, I-||Iodine, I2|
|Sulfate, SO42-||Oxygen, O2|
|Nitrate, NO3-||Oxygen, O2|
Predict the product formed at the positive electrode during the electrolysis of concentrated sodium chloride solution.
Chlorine will be produced.
Predict the product formed at the positive electrode during the electrolysis of concentrated sodium sulfate solution.
Oxygen will be produced.