Question

Which of the following represent the plot of ${\Lambda }_m$ vs $\sqrt{C}$ for a strong electrolyte ($KCl$)?

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

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

For strong electrolyte molar conductivity increases with dilution due to decrease in ion- ion force of attraction.

As strong electrolytes are mostly in ionized state, no abrupt change in the number of ions with dilution.

Thus, ${\Lambda }_m$ increases slowly with dilution.

In concentrated solution there will be a strong attraction between ions which slows down the movement of ion.

On dilution of strong electrolyte, distance between the ions increases which results in decrease in ion-ion attraction. So, there will be overall increase in molar conductance of the solution.

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 : $-A$
Thus, the extrapolation of line gives ${\Lambda }_m^0$ for strong electrolytes.