Q45 / 120 · NEET 2010 (Mains) · Chemistry

Which of the following expressions correctly represents the equivalent conductance at infinite dilution of $\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3$. Given that $\Lambda_{\mathrm{Al}^{3+}}^{\circ}$ and $\Lambda_{\mathrm{SO}_4^{2-}}^{\circ}$ are the equivalent conductances at infinite dilution of the respective ions?

  • A
    $2 \Lambda_{\mathrm{Al}^{3+}}^{\circ}+3 \mathrm{\Lambda}_{\mathrm{SO}_4^{2-}}^{\circ}$
  • Correct answer
    B
    $\Lambda_{\mathrm{Al}^{3+}}^{\circ}+\Lambda_{\mathrm{SO}_4^{2-}}^{\circ}$
  • C
    $\left(\Lambda_{\mathrm{Al}^{\circ+}}^{\circ}+3 \Lambda_{\mathrm{SO}_4^{2-}}^{\circ}\right) \times 6$
  • D
    $\frac{1}{3} \Lambda_{\mathrm{Al}^{3+}}^{\circ}+\frac{1}{2} \Lambda_{\mathrm{SO}_4^{2-}}^{\circ}$

Solution

$\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3 \rightleftharpoons 2 \mathrm{Al}^{3+}+3 \mathrm{SO}_4^{2-}$ Since equivalent conductances are given only for ions, the equivalent conductance at infinite dilution, $$ \Lambda_{\mathrm{eq}}^{\infty}=\Lambda_{\mathrm{Al}^{3+}}^{\circ}+\Lambda_{\mathrm{SO}_4^{2-}}^{\circ} $$

Hence, the correct answer is option: 'B'.

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