Question

Select the incorrect statement(s) regarding conductivity of electrolytic (ionic) solution.

• A. It increases with increases in temperaure.
• B. It decreases with increase in viscosity of solvent
• C. It decreases with increases in temperaure.
• D. It increases with increase in size of solvated ions

Answer 1

Answer: (C), (D)

It increases with increase in size of solvated ions

Factor affecting electrolytic conductance/resistance:
(a) Solute- Solute interaction:
When inter–ionic force of attraction​ between solute is higher, the resistance will be higher. Thus, lower will be the conductance.
$\text{Attractive force}\propto \text{Charge of ions}$

(b) Solute - solvent interaction:
It is an interaction of a solute with the solvent. It restricts the free motion of ions, thus, decreasing conductance​. It is actually the solvation/ hydration of ions​.

Greater the solvation​, greater will be the resistance.

$\text{Solvation}\propto \text{Change on ions}\propto \frac{1}{\text{Size}}$

Smaller the size of ions, greater will be the solvation. Thus, greater the size of solvated ion, lower will be the resistance and greater will be the resistance.

On dilution, the solute - solvent interactions decrease​. Thus, the ionic mobility and ​conductance increases.​

(c) Solvent - Solvent interaction:
It is actually the viscosity of the solvent and it describes the internal ​friction of a moving fluid.

Greater the viscosity of solvent​, greater will be the resistance ​and lesser will be the ionic mobility and the conductance.

(d) Temperature
$\text{Temperature}\propto \frac{1}{\text{Resistance}}$

$\text{Temperature}\propto \text{Conductance}$

Thus, increase in temperature will increase the conductance.