Question

The molar conductances of Ba(OH)$_2$, BaCl$_2$ and NH$_4$Cl at infinite dilution are 523.28, 280.0 and 129.8 S cm$^2$ mol$^{-1}$ respectively. The molar conductance of NH$_4$OH at infinite dilution will be

• A. 125.72 S cm$^2$ mol$^{-1}$
• B. 251.44 S cm$^2$ mol$^{-1}$
• C. 502.88 S cm$^2$ mol$^{-1}$
• D. 754.32 S cm$^2$ mol$^{-1}$

Hint:

Using a simple frame or just bolding for the box Key Points: Kohlrausch's Law: $\Lambda_m^0(\text{Electrolyte) = \nu_+ \lambda^0_+ + \nu_- \lambda^0_-$, where $\nu$ are stoichiometric coefficients. Limiting molar conductivity ($\Lambda_m^0$) of weak electrolytes can be found by algebraic manipulation of $\Lambda_m^0$ values of strong electrolytes containing the constituent ions. Ensure the ions you don't need (Ba$^{2+$, Cl$^-$) cancel out correctly. Pay attention to stoichiometry (e.g., using $\frac{1{2$ for Ba(OH)$_2$ and BaCl$_2$).