Question

Give a reason for the following

The blue color of aqueous copper sulfate solution fades when it is electrolysed using platinum electrodes

Answer 1

The blue color of aqueous copper sulfate solution fades when it is electrolyzed using platinum electrodes because,

• When copper sulfate solution is electrolyzed with copper electrodes, the blue copper ions are discharged at the cathode and get deposited as copper. For every copper ion ${\mathrm{Cu}}^{+2}$ discharged from the cathode as the neutral copper atom$\mathrm{Cu}$, a copper ion ${\mathrm{Cu}}^{+2}$ is released or added to the solution from the anode and so the total number of ${\mathrm{Cu}}^{+2}$ ions remains the same in the solution. Therefore the blue color of ${\mathrm{CuSO}}_4$does not fade in electrolytic reaction.
• But if we use platinum electrodes, For every copper ion ${\mathrm{Cu}}^{+2}$ discharged from the cathode as the neutral copper atom$\mathrm{Cu}$, There will be no copper ions get discharged from the anode, since platinum electrodes don't provide copper ions. hence the concentration of copper ions decreases during electrolysis. so the blue color of aqueous copper sulfate solution fades when it is electrolyzed using platinum electrodes