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. ${\Lambda }_m^{\circ }\left(NaN{O}_3\right)$	1. Can be obtained by Kohlrausch’s law
$Q.{\Lambda }_m^{\circ }\left(C_2{H}_{5}COOH\right)$	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 ${\Lambda }_m^{\circ }$
S. Ionic conductance	4. Velocity of the ion under electric field of 1 V $c{m}^{-1}$

$\begin{array}{cccc}P& Q& R& S\end{array}$

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

Answer 1

Answer: (D)

For strong electrolytes, ${\Lambda }_m$ and molarity (C) are related by Onsager’s eq. as
${\Lambda }_m={\Lambda }_m^{\circ }-A\sqrt{C}$
A plot of ${\Lambda }_{m}vs\sqrt{C}$ (abscissa) would be a straight line with intercept on y-axis =${\Lambda }_m^{\circ }$
(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,
${\Lambda }^{\circ }{c}_2{H}_{5}COOH={\Lambda }^{\circ }{c}_2{H}_{5}CO{O}^{-}+{\wedge }^{\circ }{H}^{+}$