Q50 / 180 · KCET 2020 · Chemistry

The pair of electrolytes that posses same value for the constant $(A)$ in the Debye-Huckel-Onsager equation, $\Lambda_{m}=\Lambda_{m}^{\circ}-A \sqrt{C}$ is

  • A
    $\mathrm{MgSO}_{4}, \mathrm{NaSO}_{4}$
  • Correct answer
    B
    $\mathrm{NH}_{4} \mathrm{Cl}, \mathrm{NaBr}$
  • C
    $\mathrm{NaBr}, \mathrm{MgSO}_{4}$
  • D
    $\mathrm{NaCl}, \mathrm{CaCl}_{2}$

Solution

$\Lambda_{m}=\Lambda_{m}^{\circ}-A \sqrt{C}$ Out of all the given pairs, the pair having same (similar) charges will possess the same value of $A$. Here, $\mathrm{MgSO}_{4}$ and $\mathrm{Na}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Mg}^{2+}$ and $\mathrm{Na}^{+}$ $\mathrm{NH}_{4} \mathrm{Cl}$ and $\mathrm{NaBr} \rightarrow \mathrm{NH}_{4}^{+}$and $\mathrm{Na}^{+}$ $\mathrm{NaBr}$ and $\mathrm{MgSO}_{4} \rightarrow \mathrm{Na}^{+}$and $\mathrm{Mg}^{2+}$ $\mathrm{NaCl}$ and $\mathrm{CaCl}_{2} \rightarrow \mathrm{Na}^{+}$and $\mathrm{Ca}^{2+}$ So, only in $\mathrm{NH}_{4} \mathrm{Cl}$ and $\mathrm{NaBr}$, the charge is same on both the cations and hence, there will have same value of $A$.

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

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