What is the primary difference between metallic and electrolytic conductance?

The fundamental difference lies in the charge carriers and the mechanism of conduction. In metallic conductance, electricity is carried by the movement of free electrons within the metal lattice, without any material transport. The metal itself remains unchanged. In contrast, electrolytic conductance involves the movement of ions (cations and anions) through the solution. This movement is accompanied by the transport of matter, as ions physically migrate towards the electrodes, leading to chemical changes at the electrode surfaces (e.g., deposition, gas evolution). Metallic conductance generally decreases with increasing temperature, while electrolytic conductance generally increases.

Why does molar conductivity decrease with increasing concentration for both strong and weak electrolytes?

For strong electrolytes, as concentration increases, the interionic attractive forces (both ion-ion and ion-solvent) become more significant. These forces hinder the independent movement of ions, effectively reducing their mobility and thus decreasing the molar conductivity. For weak electrolytes, increasing concentration means a lower degree of dissociation (according to Ostwald's dilution law). Although there are more electrolyte molecules, a smaller fraction of them are dissociated into ions, leading to a decrease in the effective number of charge carriers per mole of electrolyte, hence a decrease in molar conductivity.

How does temperature affect electrolytic conductance?

Increasing temperature generally enhances electrolytic conductance. This is primarily due to two reasons: Firstly, higher temperatures increase the kinetic energy of the ions, causing them to move faster and more frequently. This increased mobility allows for more efficient charge transport. Secondly, an increase in temperature typically decreases the viscosity of the solvent, reducing the frictional resistance encountered by the moving ions. Both these factors contribute to a higher rate of ion migration and, consequently, increased conductance.

What is the significance of the cell constant in conductivity measurements?

The cell constant ($G^* = l/A$) is a crucial geometric factor that accounts for the specific dimensions of the conductivity cell used. Since conductivity ($\kappa$) is defined for a unit volume, the measured resistance ($R$) or conductance ($G$) of a solution in a cell needs to be normalized by the cell's geometry. The cell constant allows us to convert the measured conductance ($G$) into specific conductivity ($\kappa = G \cdot G^*$), making the conductivity value independent of the particular cell used. It ensures that conductivity measurements are comparable across different experimental setups.

Can Kohlrausch's Law be applied to strong electrolytes?

Yes, Kohlrausch's Law is fundamentally applicable to both strong and weak electrolytes, but its utility is most pronounced for weak electrolytes. For strong electrolytes, the law states that their molar conductivity at infinite dilution ($\Lambda_m^\circ$) is the sum of the limiting molar conductivities of their constituent ions. This is because strong electrolytes are completely dissociated even at moderate concentrations, and at infinite dilution, interionic interactions become negligible. For weak electrolytes, however, direct extrapolation of $\Lambda_m$ to infinite dilution is not possible, making Kohlrausch's Law an indispensable tool for calculating their $\Lambda_m^\circ$ indirectly using values from strong electrolytes.

Electrolytic Conductance

Chemistry

NEET UG

Version 1Updated 22 Mar 2026

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Electrolytic conductance refers to the ability of an electrolyte solution to conduct electricity due to the movement of ions. Unlike metallic conductors where charge is carried by electrons, in electrolytic solutions, it is the migration of positively charged cations towards the cathode and negatively charged anions towards the anode that facilitates the flow of current. This phenomenon is fundame…

Quick Summary

Electrolytic conductance is the ability of an electrolyte solution to conduct electricity through the movement of ions. Unlike metals, where electrons are charge carriers, in solutions, it's the migration of cations towards the cathode and anions towards the anode.

Key terms include resistance ( $R$ , in $\Omega$ ), its reciprocal conductance ( $G$ , in S), resistivity ( $\rho$ , in $\Omega \cdot \text{m}$ ), and its reciprocal conductivity ( $\kappa$ , in $\text{S} \cdot \text{m}^{-1}$ ).

Conductivity is related to conductance by the cell constant ( $G^* = l/A$ ), where $\kappa = G \cdot G^*$ . Molar conductivity ( $\Lambda_m$ ) normalizes conductivity by concentration ( $C$ ), given by $\Lambda_m = \kappa/C$ (or $\Lambda_m = (\kappa \times 1000)/C$ for common units).

Factors influencing conductance include the nature of the electrolyte (strong vs. weak), its concentration ( $\kappa$ increases with concentration, $\Lambda_m$ decreases), temperature (increases conductance), and the nature of the solvent.

Kohlrausch's Law states that at infinite dilution, each ion contributes independently to the total molar conductivity, allowing calculation of $\Lambda_m^\circ$ for weak electrolytes and their degree of dissociation.

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Key Concepts

Relationship between Resistance, Resistivity, Conductance, and Conductivity

These terms are interconnected and describe a material's ability to oppose or facilitate current flow.…

Molar Conductivity and its Variation with Concentration

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Applications of Kohlrausch's Law

Kohlrausch's Law is particularly powerful for determining the molar conductivity at infinite dilution…

Conductance (G): —

G = 1/R

(Units: S or

\Omega^{-1}

)

Conductivity ($\kappa$): —

\kappa = 1/\rho = G \cdot G^*

(Units:

\text{S} \cdot \text{m}^{-1}

\text{S} \cdot \text{cm}^{-1}

)

**Cell Constant (

G^*

):**

G^* = l/A

(Units:

\text{m}^{-1}

\text{cm}^{-1}

)

Molar Conductivity ($\Lambda_m$): —

\Lambda_m = \kappa/C

(SI Units:

\text{S} \cdot \text{m}^2 \cdot \text{mol}^{-1}

)

Common Units for $\Lambda_m$: —

\Lambda_m = (\kappa \times 1000)/C

(for

\kappa

\text{S} \cdot \text{cm}^{-1}

C

\text{mol/L}

\Lambda_m

\text{S} \cdot \text{cm}^2 \cdot \text{mol}^{-1}

)

Kohlrausch's Law: —

\Lambda_m^\circ = \nu_+ \lambda_+^\circ + \nu_- \lambda_-^\circ

Degree of Dissociation ($\alpha$): —

\alpha = \Lambda_m / \Lambda_m^\circ

Effect of Temperature: — Electrolytic conductance increases with temperature.

Effect of Concentration: —

\kappa

increases with concentration;

\Lambda_m

decreases with concentration.

To remember the factors affecting electrolytic conductance: 'N.C.T.S.I.'

Nature of electrolyte (Strong vs. Weak)

Concentration (

\kappa

up,

\Lambda_m

down with concentration)

Temperature (Conductance up with temperature)

Solvent (Nature of solvent, viscosity)

Ion size and solvation (Effective size of hydrated ions)