What is the primary difference between metallic and electrolytic conduction?

The fundamental difference lies in the charge carriers and the mechanism of conduction. In metallic conduction, free electrons are responsible for carrying the electric current, and there is no material transfer. In contrast, electrolytic conduction involves the movement of ions (cations and anions) through the solution. This ionic movement results in the transfer of matter, often leading to chemical changes at the electrodes (e.g., deposition or gas evolution). Additionally, metallic conduction generally decreases with increasing temperature, while electrolytic conduction typically increases with temperature due to enhanced ion mobility.

Why does molar conductivity increase with dilution for both strong and weak electrolytes?

For strong electrolytes, as dilution increases, the interionic attractive forces between ions decrease significantly. This allows ions to move more freely and with less hindrance, leading to an increase in their ionic mobility and thus an increase in molar conductivity. For weak electrolytes, dilution not only reduces interionic attractions but, more importantly, it increases the degree of dissociation ($alpha$) of the electrolyte. A higher degree of dissociation means more ions are formed per mole of electrolyte, which directly contributes to a higher molar conductivity.

How is the cell constant determined for a conductivity cell?

The cell constant ($G^* = l/A$) is a characteristic property of a specific conductivity cell and remains constant for that cell. It is typically determined by measuring the resistance ($R$) of the cell when it contains a standard solution of known conductivity ($kappa$). A common standard solution is a KCl solution of a specific concentration (e.g., 0.01 M, 0.1 M, or 1 M) at a particular temperature. Since $kappa = G cdot G^* = (1/R) cdot G^*$, the cell constant can be calculated as $G^* = kappa cdot R_{measured}$. Once determined, this cell constant can then be used to find the conductivity of any other solution by simply measuring its resistance in the same cell.

What is the significance of Kohlrausch's Law?

Kohlrausch's Law of Independent Migration of Ions is highly significant for two main reasons. Firstly, it allows us to calculate the limiting molar conductivity ($Lambda_m^0$) of weak electrolytes. Since $Lambda_m$ for weak electrolytes cannot be accurately determined by extrapolation from $Lambda_m$ vs. $sqrt{C}$ plots, Kohlrausch's law enables its calculation from the limiting molar conductivities of strong electrolytes. Secondly, it helps in determining the degree of dissociation ($alpha = Lambda_m / Lambda_m^0$) of weak electrolytes at any given concentration, which in turn allows for the calculation of their dissociation constants ($K_a$ or $K_b$). This law underscores the independent contribution of each ion to the total conductivity at infinite dilution.

Why does conductivity ($kappa$) decrease with dilution, while molar conductivity ($Lambda_m$) increases?

This is a common point of confusion. Conductivity ($kappa$) is defined as the conductance of a unit volume of solution. When a solution is diluted, the total number of ions in a given unit volume decreases. Even though the mobility of individual ions might increase slightly, the reduction in the number of charge carriers per unit volume is the dominant factor, leading to a decrease in $kappa$. Molar conductivity ($Lambda_m$), on the other hand, is defined as the conductivity produced by one mole of electrolyte. As dilution increases, the volume containing one mole of electrolyte increases, and the ions within that volume experience less interionic attraction and, for weak electrolytes, greater dissociation. Both these factors contribute to a net increase in the conducting power per mole of electrolyte, hence $Lambda_m$ increases.

Conductance in Electrolytic Solutions

Chemistry

NEET UG

Version 1Updated 22 Mar 2026

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Conductance in electrolytic solutions refers to the ability of a solution containing dissolved ions (electrolytes) to carry an electric current. Unlike metallic conductors where charge is carried by free electrons, in electrolytic solutions, the charge carriers are ions, which migrate towards oppositely charged electrodes. This phenomenon is fundamental to electrochemistry, enabling processes like…

Quick Summary

Conductance in electrolytic solutions describes the ability of a solution containing ions to carry electric current. Unlike metals where electrons are the charge carriers, here, dissolved ions migrate towards oppositely charged electrodes.

Electrolytes, substances that dissociate into ions in solution, are classified as strong (complete dissociation, high conductance) or weak (partial dissociation, low conductance). Key terms include resistance ( $R$ , opposition to flow), resistivity ( $ho$ , intrinsic resistance), conductance ( $G=1/R$ , ease of flow), and conductivity ( $kappa=1/\rho$ , specific conductance).

Conductivity is measured using a conductivity cell, and its value depends on the cell constant ( $G^* = l/A$ ), where $kappa = G cdot G^*$ . Molar conductivity ( $Lambda_m$ ) quantifies the conducting power of one mole of electrolyte, defined as $Lambda_m = kappa/C$ .

$Lambda_m$ increases with dilution for both strong (due to reduced interionic attraction) and weak electrolytes (due to increased dissociation). Kohlrausch's Law states that at infinite dilution, $Lambda_m^0$ is the sum of individual ionic conductivities, allowing calculation of $Lambda_m^0$ for weak electrolytes and their degree of dissociation.

Factors like temperature, concentration, and ion mobility significantly influence conductance.

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Key Concepts

Conductivity (

kappa

) and Cell Constant (

G^*

)

Conductivity, or specific conductance, is an intrinsic property of an electrolytic solution, indicating its…

Molar Conductivity (

Lambda_m

) and its dependence on concentration

Molar conductivity ( $Lambda_m$ ) is a measure of the conducting power of all the ions produced by one mole of…

Kohlrausch's Law and its applications

Kohlrausch's Law of Independent Migration of Ions states that at infinite dilution, where interionic…

Resistance ($R$): — Opposition to current flow (

Omega

Conductance ($G$): —

1/R

(S).

Resistivity ($ ho$): — Resistance of unit length/area (

Omega cdot m

Conductivity ($kappa$): —

1/\rho = G cdot G^*

(

S cdot m^{-1}

S cdot cm^{-1}

G^* = l/A

(cell constant).

Molar Conductivity ($Lambda_m$): —

kappa/C

. If

kappa

S cdot cm^{-1}

C

mol cdot L^{-1}

, then

Lambda_m = \frac{kappa \times 1000}{C}

(

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

Limiting Molar Conductivity ($Lambda_m^0$): —

Lambda_m

at infinite dilution.

Kohlrausch's Law: — $Lambda_m^0 =

u_+ lambda_+^0 + u_- lambda_-^0$.

Degree of Dissociation ($alpha$): —

alpha = Lambda_m / Lambda_m^0

Weak Electrolyte Dissociation Constant ($K_a$): —

K_a = \frac{Calpha^2}{1-alpha}

Trends: —

kappa

decreases with dilution.

Lambda_m

increases with dilution (for both strong and weak electrolytes).

To remember factors affecting electrolytic conductance: Nice Cats Try Solving Ions.

Nature of electrolyte (strong/weak)

Concentration

Temperature

Solvent properties (viscosity, dielectric constant)

Ion size and charge