Question

The equivalent conductances of two strong electrolytes at infinite dilution in $H _2 O$ (where ions move freely through a solution) at $25^{\circ} C$ are given below :
$\Lambda_{ CH _3 COONa }^{\circ}=91.0 S cm ^2 /$ equivalent
$\Lambda_{ HCl }^{\circ}=426.2 S cm ^2 /$ equivalent.
What additional information/quantity one needs to calculate $\Lambda^{\circ}$ of an aqueous solution of acetic acid?

• A. $\Lambda^{\circ}$ of chloroacetic acid $ClCH _2 COOH$
• B. $\Lambda^{\circ}$ of $NaCl$
• C. $\Lambda^{\circ}$ of $CH _3 COOK$
• D. The limiting equivalent conductance of $H ^{+} \lambda_{ H ^{+}}^0$

Answer 1

Answer: (B)

According to Kohlrausch's law, the molar conductivity at infinite dilution $\Lambda^{\circ}$ for weak electrolyte, $CH _3 COOH$ is
$\Lambda_{ CH _3 COOH }^{\circ}=\Lambda_{ CH _3 COONa }^{\circ}+\Lambda_{ HCl }^{\circ}-\Lambda_{ NaCl }^{\circ}$
So, for calculating the value of $\Lambda_{ CH _3 COOH }^{\circ}$, value of $\Lambda_{ NaCl }^{\circ}$ should also be known.