Question

Which of the following graph is correct?

${\Lambda }_m$ - Molar conductivity
$C$ - concentration of electrolyte

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Variation in molar conductivity of strong electrolyte due to ion-ion interaction is given by an empirical relation proposed by kohlrausch.

${\Lambda }_m={\Lambda }_m^0-A\sqrt{C}$
${\Lambda }_m$ - Molar conductivity
${\Lambda }_m^0$ - Limiting molar conductivity
$C$ is concentration of electrolyte
$A$ is constant for a given solvent and temperature.

${\Lambda }_m={\Lambda }_m^0-A\sqrt{C}$
This equation is in the form of straight line equation,
$y=c+mx$
$\therefore$
Plot of ${\Lambda }_{m}vs\sqrt{C}$



Intercept : ${\Lambda }_m^0$
Slope : $-A$

All electrolytes of a particular type have the same value for ‘A’.
Since $KCl$ and $NaCl$ are of same type (equal charge on cation and anion), they have similar $A$ value which means they have a same slope. So, their will be of parallel to each other.


Thus, graph (c) is incorrect.

$KCl$ and $MgS{O}_4$ is of different type of electrolyte, charges on cations and anions are ,
$KCl\Rightarrow +1,-1MgS{O}_4\Rightarrow +2,-2$
So they have different slope hence, they dont have a parallel lines.
Thus, graph (b) is incorrect.

In graph (d), we have $C{H}_{3}COOH$ which is a weak electrolyte. Weak electrolyte will have a rectangular parabola curve and it does not intercept the y-axis.
Thus, graph (d) is also incorrect.

Hence, graph (a) is the correct one.