Question

Define limiting molar conductivity. Why does the conductivity of an electrolyte solution decrease with the decrease in concentration?

Answer 1

Hint : The limiting molar conductivity is defined as molar conductivity of the solution at infinite dilution. Hence we can say that the conductivity of an electrolyte at approximately at zero concentration is called limiting molar conductivity. Value of limiting molar conductivity is always less than unity. It can be determined with the help of Kohlrausch’s law.

Complete step step solution:
> According to the Kohlrausch’s law at infinite dilution the molar conductivity of an electrolyte is the sum of the ionic conductivities of anions and cations. Mathematically the > Kohlrausch’s law can be represented as;
${\lambda _m} = {\lambda ^o}_m - K\sqrt c $; where ${\lambda ^o}_m$ is molar conductivity of electrolyte at infinite dilution, ${\lambda _a}$ is molar conductivity, $K = $ Kohlrausch coefficient, $c = $ concentration.
> We can determine the answer of this problem with the help of the above equation. For strong electrolyte molar conducting can be determined with the molar conductivity v/s concentration cure while for weak electrolyte it can not be determined by the curve. So from the above equation we can see that when concentration of electrolyte (which is represented by $c$ in the equation) decreases the value of molar conductivity will also be decreasing , Thus conductivity of an electrolyte solution decreases with the decrease in concentration.
> Theoretically we can say that the number of ions per unit volume decreases on dilution so conductivity decreases.

Note : We have learned that limiting molar conductivity is achieved when the concentration of the electrolyte in the solution approaches zero. As when the solution becomes very dilute then conductivity decreases because as the number of ions per unit volume decreases. As the result, the conductivity of an electrolyte solution decreases with the decrease in concentration.