Question

Consider the statements S1 and S2 :
S1 : Conductivity always increases with decrease in the concentration of electrolyte.
S2 : Molar conductivity always increases with decrease in the concentration of electrolyte.
The correct option among the following is:

• A. S1 is correct and S2 is wrong
• B. S1 is wrong and S2 is correct
• C. Both S1 and S2 are wrong
• D. Both S1 and S2 are correct

Answer 1

The correct option is B S1 is wrong and S2 is correct

The explanation of statements (S1 and S2 ) are as follows : In conductivity cell, conductivity $\left(\kappa \right)$ is equal to the sum of ionic conductances (c), of an electrolytic solution present is unit volume of the solution enclosed by two electrodes of unit area $(a\ne 1)$ separated by a unit length $(l=1)$.
$\kappa =c\times \frac{l}{a}$
$\kappa =c$ when $l=1,a=1$
So, with decrease in the concentration of electrolyte, number of ions in the given unit volume also decreases, i.e. $\kappa$ [conductivity] also decreases. Thus, statement S1 is wrong. S2 : Molar conductivity ${\lambda }_m$ is defined as the conducting power of all the ions present in a solution containing 1 mole of an electrolyte.
In a conductivity cell,
${\lambda }_m\propto \frac{1}{M}$
i.e. molar conductivity increases with decrease in the concentration (M) of electrolyte. Thus, statement S2 is correct.