Molar conductivity

Molar conductivity

Molar conductivity refers to the measure of the electrical conductivity of an electrolyte solution divided by the concentration of the electrolyte. It is a key parameter in understanding the behavior of ions in solution and is denoted by the symbol Λm. Molar conductivity increases with the decrease in concentration, reaching a maximum value at infinite dilution, where the ions are free from interionic interactions.

Definition

Molar conductivity, Λm, is defined as the conductivity (κ) of an electrolyte solution divided by the concentration (c) of the electrolyte, where the concentration is expressed in moles per liter (mol/L). Mathematically, it is given by:

\[ \Lambda_m = \frac{\kappa}{c} \]

where:

• \(\kappa\) is the conductivity of the solution in Siemens per meter (S/m),
• \(c\) is the concentration of the electrolyte in mol/L.

Units

The SI unit of molar conductivity is S m²/mol, although it is often expressed in more practical units such as mS cm²/mol for aqueous solutions at room temperature.

Factors Affecting Molar Conductivity

Several factors influence the molar conductivity of an electrolyte solution:

• **Concentration**: As the concentration decreases, molar conductivity increases due to the reduced interaction between ions.
• **Temperature**: Increasing the temperature generally increases molar conductivity because of the enhanced mobility of the ions.
• **Nature of the Electrolyte**: Strong electrolytes (which completely dissociate into ions in solution) have higher molar conductivities than weak electrolytes (which only partially dissociate).

Kohlrausch's Law

Kohlrausch's Law of Independent Migration of Ions states that at infinite dilution, each ion contributes to the conductivity of the electrolyte independently of the other ions present in the solution. The law allows for the calculation of the molar conductivity of a strong electrolyte at infinite dilution by summing the contributions of its individual ions.

Applications

Molar conductivity is used in various applications, including:

• Determining the degree of dissociation of electrolytes.
• Studying the kinetics of electrochemical reactions.
• Analyzing the purity of water and other solvents.

See Also

• Electrolyte
• Electrical Conductivity
• Kohlrausch's Law of Independent Migration of Ions
• Electrochemistry