Question

On what basis is the discharge potential of ion determined?

Answer 1

Discharge potential:

• The potential at which the ion is deposited or discharged is termed the discharge potential.
• Different ions have different values of discharge potential.
• Discharge potential is coined as the tendency of an ion to gain electrons and in turn to get reduced.
• Discharge potential depends upon the reduction potential.
• More is its tendency to get reduced, mole will be the value of reduction potential.
• The discharge potential can be explained as the potential at which an ion is discharged.
• In the electrolysis of an electrolytic solution that consists of more than two ions, all the ions are not discharged at the electrodes simultaneously but certain ions are liberated at the electrodes in preference to others. This can be explained by the preferential discharge theory.
• The preferential discharge theory states that if more than one type of ion is attracted towards a particular electrode, then the one discharged is the ion that requires the least energy.

Example:

• In the electrolysis of $\mathrm{NaCl}$ solution due to the ionization of water Sodium chloride, the solution contains ${\mathrm{H}}^{+}$ and ${\mathrm{OH}}^{–}$ ions apart from ${\mathrm{Na}}^{+}$ and ${\mathrm{Cl}}^{–}$ions.
• When the potential difference is applied between the two electrodes, ${\mathrm{Na}}^{+}$ and ${\mathrm{H}}^{+}$ ions move towards the cathode, and ${\mathrm{Cl}}^{–}$ and ${\mathrm{OH}}^{–}$ ions move towards the anode.
• Since Hydrogen has a higher reduction potential than Sodium ${\mathrm{H}}^{+}$ions get reduced at the cathode in preference to giving Hydrogen gas as Hydrogen has a higher reduction potential than Sodium likewise ${\mathrm{Cl}}^{–}$ ions are oxidized at the anode in preference to ${\mathrm{OH}}^{–}$ giving Chlorine gas.