Question

(a) Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution:
$A{g}^{+}\left(aq\right)+e\to Ag\left(s\right)E^{\circ }=+.80V$
$H^{+}\left(aq\right)+e^{-}\to \frac{1}{2}{H}_2\left(g\right)E^o=0.00V$
On the basis of their standard reduction electrode potential $\left(E^o\right)$ values, which reaction is feasible at the cathode and why?
(b) Define limiting molar conductivity. Why conductivity of an electrolyte solution decrease with decrease in concentration?

Answer 1

The relationship between the standard free energy change and emf of a cell reaction is given by:
$\Delta G^{\circ }=-nF{E}^{\circ }$
Thus, more positive the standard reduction potential of a reaction, the more negative is the standard free energy change associated with the process and, consequentely, the higher is the feasibility of the reaction .
Since, $E^{\circ }A{g}^{+}/Ag$ has a greater positive value than $E^{\circ }{H}^{+}/H$ the reaction which is feasible at the cathode is given by
$A{g}^{+}(aq{)}^{+}{e}^{-}\to Ag(s)$.
(b) The limiting molar conductivity of an electrolyte is defined as its molar conductivity when the concentration of the electrolyte in the solution approaches zero.
The conductivity of an electrolyte solution is the conductance of ions present in a unit volume of the solution. The number of ions (responsible for carrying current) decrease when the solution is diluted or the concentration of an electrolyte solution decrease with the decrease in concentration.