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Electrolysis : Kohlrausch's Law
The independent movement of the ions of a salt assumed in the theory of electrolytic dissociation provides a simple explanation of a result discovered experimentally by in 1875 viz., that the equivalent conductivity of a salt at dilution is the sum of two parts, one depending only on the cation and the other only on the anion:
Λ∞ = lc + la.
This is known as Kohlrausch's law. For example:
KCl Λ∞ = 130.0
KNO3 Λ∞ = 126.3
NaCl Λ∞ = 108.9
NaNO3 Λ∞ = 105.2
Λ∞KCl - Λ∞KNO3 = 3.7
Λ∞KCl - Λ∞NaCl = 21.1
Λ∞NaCl - Λ∞NaNO3 = 3.7
Λ∞KNO3 - Λ∞NaNO3 = 21.1
The value 3.7 is the difference in la values for Cl and NO3, and the value 21.1 is the difference in lc values for K and Na: la and lc are called the mobilities of the anion and cation, respectively, expressed in conductivity units.
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