How will the pH of brine (aq NaCl solution) be affected when it is electrolysed?
The pH of the solution will rise as NaOH is formed in the electrolytic cell. Chemical reaction occurring at cell when aqueous brine solution is electrolysed are as follows
$$\begin{aligned} & \mathrm{NaCl}(a q) \xrightarrow{\mathrm{H}_2 \mathrm{O}} \mathrm{Na}^{+}(a q)+\mathrm{Cl}^{-}(a q) \\ & \text { Cathode } \mathrm{H}_2 \mathrm{O}(l)+e^{-} \longrightarrow \frac{1}{2} \mathrm{H}_2(g)+\mathrm{OH}^{-}(a q) \\ & \text { Anode Cl }(a q) \longrightarrow \frac{1}{2} \mathrm{Cl}_2(g)+e^{-} \\ \text{Net reaction}\quad& \mathrm{NaCl}(a q)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{Na}^{+}(a q)+\mathrm{OH}^{-}(a q)+\frac{1}{2} \mathrm{H}_2+\frac{1}{2} \mathrm{Cl}_2 \end{aligned}$$
Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why ?
Life time of any cell depends upon ions present in cell. Ions are not involved in the overall cell reaction of mercury cell. Hence, mercury cell has a constant cell potential throughout its useful life.
Solutions of two electrolytes $A$ and $B$ are diluted. The $\Lambda_m$ of ' $B$ ' increases 1.5 times while that of $A$ increases 25 times. Which of the two is a strong electrolyte ? Justify your answer.
Strong electrolytes dissociate almost completely even on high concentration. Therefore, concentration of such solutions remain almost same on dilution. Electrolyte ' $B$ ' is stronger than ' $A$ ' because in ' $B$ ' the number of ions remains the same on dilution, but only interionic attraction decreases.
Therefore, $\Lambda_m$ increases only 1.5 times. While in case of weak electrolyte on dilution, number of constituent ions increases.
When acidulated water (dil. $\mathrm{H}_2 \mathrm{SO}_4$ solution) is electrolysed, with pH of the solution be affected ? Justify your answer.
Since pH of solution depends upon concentration of $\mathrm{H}^{+}$presence in solutions. pH of the solution will not be affected as $\left[\mathrm{H}^{+}\right]$remains constant.
At anode $2 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{O}_2+4 \mathrm{H}^{+}+4 \mathrm{e}^{-}$
At cathode $4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \longrightarrow 2 \mathrm{H}_2$
In an aqueous solution how does specific conductivity of electrolytes change with addition of water?
Conductivity of solution due to total ions present in per unit volume of solution is known as specific conductivity. Specific conductivity decreases due to decrease in the number of ions per unit volume. We add water to aqueous solution, number of ions present in per unit volume decreases.