CBSE Class 12 Chemistry sample paper 2023-24: question 23

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1. (a) Yes, provided the ZnSO₄ concentrations in the two half-cells differ (a concentration cell). Then the two electrode potentials are unequal, giving $E_{cell}=\frac{0.059}{2}\log \frac{[Z{n}^{2+}{]}_{cathode}}{[Z{n}^{2+}{]}_{anode}}\ne 0$. With equal concentrations, $E_{cell}=0$.

   1 mark

2. (b) By Kohlrausch's law: ${\Lambda }_m^0(\mathrm{MgC}{\mathrm{l}}_2)={\lambda }_m^0(\mathrm{M}{\mathrm{g}}^{2+})+2{\lambda }_m^0(\mathrm{C}{\mathrm{l}}^{-})$, so $258.6=106+2{\lambda }_m^0(\mathrm{C}{\mathrm{l}}^{-})$ and ${\lambda }_m^0(\mathrm{C}{\mathrm{l}}^{-})=\frac{152.6}{2}=76.3\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$.

   1 mark

3. (c) $\kappa =\frac{G^{\ast }}{R}=\frac{0.146\mathrm{c}{\mathrm{m}}^{-1}}{1000\Omega }=1.46\times 10^{-4}\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$

   1 mark

Answer: (a) Yes, if ZnSO₄ concentrations differ (concentration cell); (b) 76.3 S cm² mol⁻¹; (c) 1.46 × 10⁻⁴ S cm⁻¹

Revise the chapter

• Chapter: Electrochemistry (notes, formulas, where marks are lost and every past question)