Kohlrausch's Law, also known as the law of independent migration of ions, states that at infinite dilution, the equivalent conductivity of an electrolyte is the sum of the individual ionic conductivities of its cations and anions. This means that at very low concentrations, the movement of each ion is independent of the presence of other ions.
Understanding Kohlrausch's Law
The law is expressed mathematically as:
Λ₀ = λ₀⁺ + λ₀⁻
Where:
- Λ₀ is the limiting molar conductivity (conductivity at infinite dilution).
- λ₀⁺ is the limiting molar ionic conductivity of the cation.
- λ₀⁻ is the limiting molar ionic conductivity of the anion.
Practical Significance:
Kohlrausch's Law is crucial for determining the limiting molar conductivity of weak electrolytes. Since weak electrolytes don't fully dissociate, their conductivity at normal concentrations can't be directly used to calculate their limiting molar conductivity. Kohlrausch's Law allows us to extrapolate to infinite dilution, providing accurate values.
Applications:
- Determining the limiting molar conductivity of weak electrolytes: As mentioned above, this is a primary application. By knowing the limiting molar conductivities of strong electrolytes with similar ions, we can calculate the limiting molar conductivity of a weak electrolyte.
- Calculating the degree of dissociation of weak electrolytes: By comparing the measured molar conductivity with the limiting molar conductivity obtained from Kohlrausch's Law, we can determine the degree of dissociation of a weak electrolyte.
- Determining the ionic conductivity of individual ions: The law helps to determine the contribution of each ion to the overall conductivity of the electrolyte.
Examples:
- Consider the limiting molar conductivity of NaCl. By measuring the limiting molar conductivities of KCl and HCl, we can use Kohlrausch's Law to calculate the limiting molar conductivity of NaCl by subtracting the contribution of K⁺ from KCl and adding the contribution of Na⁺.
Different Names:
The law is also frequently referred to as the Law of Independent Migration of Ions, highlighting the core concept of independent ion movement at infinite dilution.
