(i) Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution :
${{Ag}^{+}}$(aq) +${{e}^{-}}$ -------» Ag(s); E° = + 0.80 V
${{H}^{+}}$(aq)+${{e}^{-}}$ -------> 1/2$H _{ 2 }$(g); E°=0.00V
On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why?
(ii) Define limiting molar conductivity. Why conductivity of an electrolyte solution decreases with the decrease in concentration ?
(i) Electrolysis of an aqueous solution of AgCl.
AgCl (aq) --------> ${{Ag}^{+}}$(aq) + ${{Cl}^{-}}${aq)
$H _{ 2 }O$ (/) ------->${{H}^{+}}$(aq) + ${{OH}^{-}}$(aq)
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On passing electricity, ${{Ag}^{+}}${aq) and ${{H}^{+}}$(aq) move towards the cathode. Since, the discharge potential of ${{Ag}^{+}}$ ion is lower than that of ${{H}^{+}}$ ions. In the other words, ${{Ag}^{+}}$ ions have more value of standard reduction potential. Therefore, Ag+ ions are discharged in preference to ${{H}^{+}}$ ions.
At cathode ${{Ag}^{+}}${aq) + ${{e}^{-}}$ -------> Ag(s)
At anode ${{Cl}^{-}}$ - ${{e}^{-}}$ ------> Cl
Cl +Cl ------> $Cl _{ 2 }$(g)
Hence, reduction of ${{Ag}^{+}}$ (ion) is feasible at cathode.
(ii) Limiting molar conductivity The molar conductivity of a solution at infinite dilution is called limiting molar conductivity and is represented by the symbol Am. Conductivity of an electrolyte solution decrease with the decrease in concentration due to the fact that the number of ions per unit volume that carry the current in a solution decreases on dilution.