Question

Match the List I with List II and select the correct answer using the code given below the lists :

List I	List II
P. $\Lambda_{m}^{∘} \left(NaNO_{3}\right)$	1. Can be obtained by Kohlrausch’s law
$Q.\Lambda_{m}^{∘} \left(C_{2}H_{5}COOH\right)$	2. Can be obtained by extrapolating $\Lambda_{m} \upsilon s$ $\left(molarity\right)^{1/2}$ graph to zero molarity
R.Ionic mobility	3. Contribution by the ion to $\Lambda_{m}^{∘}$
S. Ionic conductance	4. Velocity of the ion under electric field of 1 V $cm^{-1}$

$\begin{matrix}P&Q&R&S\end{matrix}$

• A. $\begin{matrix}4&1&2&3\end{matrix}$
• B. $\begin{matrix}3&1&2&4\end{matrix}$
• C. $\begin{matrix}1&2&3&4\end{matrix}$
• D. $\begin{matrix}2&1&4&3\end{matrix}$

Answer 1

Answer: (D)

For strong electrolytes, $Λ_{m}$ and molarity (C) are related by Onsager’s eq. as
$Λ_{m}=\Lambda_{m}^{∘}-A \sqrt{C}$
A plot of $Λ_{m} vs \sqrt{C}$ (abscissa) would be a straight line with intercept on y-axis =$\Lambda^{∘}_{m}$
(Q) For weak electrolytes (like $C_{2}H_{5}COOH$), $\Lambda_{m} vs \sqrt{C}$ is a curve which cannot be extrapolated to C = 0. From Kohlrausch law,
$\Lambda^{∘}c_{2}H_{5}COOH =\Lambda^{∘}c_{2}H_{5}COO^{-}+\wedge^{∘}H^{+}$