Question

At $ 298\, K $ the molar conductivities at infinite dilution $ \left(\Lambda m^{\circ}\right) $ of $ NH_{4}Cl, KOH $ and $ KCl $ are $ 152.8 $ , $ 272.6 $ and $ 149.8 \, S \, cm^{2} \, mol^{-1} $ respectively. The $ \left(\Lambda m^{\circ}\right) $ of $ NH_{4}OH $ in $ S\, cm^{2} \, mol^{-1} $ and $ %\ $ dissociation of $ 0.01 \, M \, NH_{4}OH $ with $ \Lambda_{m}=25.1\, S\, cm^{2}\, mol^{-1} $ at the same temperature are

• A. 275.6, 0.91
• B. 275.6, 9.1
• C. 266.6, 9.6
• D. 30, 84

Answer 1

Answer: (B)

$ \Lambda_{m}^{\circ} NH _{4} OH =\Lambda_{m}^{\circ}\left( NH _{4} Cl + KOH \right)-\Lambda_{m}^{\circ}( KCl ) $

$=152.8+272.6-149.8 $

$=275.6 \,S \,cm ^{2} \,mol ^{-1} $

Degree of dissociation $(\alpha)=\frac{\Lambda_{m}}{\Lambda^{\circ}_{m}}=\frac{25.1}{275.6}$

$=0.091$

$\therefore \%$ degree of dissociation $=9.1 \%$