The electrolysis of an aqueous solution of copper sulphate using copper electrodes (i.e. using active electrodes) results in transfer of copper metal from the anode to the cathode during electrolysis. The copper sulphate is ionised in aqueous solution.
CuSO4 ==> Cu(++) + SO4(-.-)The positively charged copper ions migrate to the cathode, where each gains two electrons to become copper atoms that are deposited on the cathode.
Cu(++) + 2e(-) ==> CuAt the anode, each copper atom loses two electrons to become copper ions, which go into solution.
Cu ==> Cu(++) + 2e(-)The sulphate ion does not take part in the reaction and the concentration of the copper sulphate in solution does not change. The reaction is completed when the anode is completely eaten away. This process is used in electroplating.
Electrolysis of an Aqueous Solution of Sodium SulphateThe electrolysis of an aqueous solution of sodium sulphate using inert electrodes produces hydrogen at the cathode and oxygen at the anode and a neutral solution of sodium sulphate remains unaltered by the electrolysis. Cathode Reaction : 4 H2O + 4 e(-) ==> 2 H2 + 4 OH(-)Anode Reaction : 2 H2O ==> O2 + 4 H(+) + 4 e(-)
The overall cell reaction is : 6 H2O ==> 2 H2 + O2 +4 H(+) +4 OH(-)
If the reaction is carried out in a <span>Hofmann </span>Voltammeter, with some universal indicator in the solution, it will be noticed that around the cathode the solution becomes alkaline and around that anode the solution becomes acidic. This is explained as follows :
<span>At the cathode :Hydrogen ions are being removed from solution, thereby leaving an excess of hydroxyl ions which makes the solution alkaline, andAt the anode :Hydroxyl ions are being removed, so leaving an excess of hydrogen ions which makes the solution acidic.</span>Electrolysis of a solution of dilute Sulphuric Acid<span>The electrolysis of an aqueous solution of dilute sulphuric acid is often carried out in a </span><span>Hofmann </span>Voltammeter, an apparatus in which the gases evolved at the anode and cathode can be collected in separate graduated tubes. When the solution is electrolyzed hydrogen is produced at the cathode and oxygen at the anode. These gases can be shown to be present in a 2 to 1 ratio and result from the electrolysis of water under acidic conditions.Sulphuric acid is a strong electrolyte is fully dissociated in aqueous solution.
H2SO4 ==> 2 H(+) + SO4(2 -)Water is a weak electrolyte and is only slightly dissociated
H2O ==> H(+) + OH(-)During electrolysis, the hydrogen ions migrates towards the cathode, and are discharged there (i.e. they gain an electron and are converted to hydrogen gas).
2 H(+) + 2 e(-) ==> H2At the anode the concentration of hydroxyl ions is too low to maintain a reaction and the sulphate ions are not oxidized but remain on in solution at the end. Water molecules must be the species reacting at the anode.
2 H2O ==> O2 + 4 H(+) + 4 e(-)The overall reaction is
<span>Cathode Reaction :2 H(+) + 2e(-) ==> H2 4 H(+) + 4e(-) ==> 2H2 Anode Reaction :<span>2 H2O ==> O2 + 4 H(+) + 4 e(-) </span>Overall Cell Reaction:4 H(+) + 2 H2O ==> 2 H2 + O2 + 4 H(+) </span>For every hydrogen ions discharged at the anode, another hydrogen ion is formed at the cathode. The net result is that the concentration of the sulphuric acid remains constant and this electrolysis consists of the decomposition of water with the overall reaction
2H2O ==> 2H2 + O2 <span></span>