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In 1875-1879, Friedrich Kohlausch established that in dilute solutions, molar conductivity could be decomposed into contributions of the individual ions. This is known as Kohlrausch’s law.
A series of experiments by J. Kohlrausch in the 1870s regarding ionic conductivity at boundless dilution led to the formulation of Kohlrausch’s law, which relates the conductance of a solution containing a number of dissolved ions to their equivalent conductance, so that if all ions were completely dissociated (given the same concentrations as in their pure state), then the conductance would equal that corresponding to the sum of equivalent conductances of all ions. This is related to the common ion effect, where the addition of one type of ion can influence the electrical properties of another type.
Define Kohlausch’s Law
The equivalent conductance of a given electrolyte during unlimited dilution is equivalent to the total of the overall conductances of both the positive and negative ions, according to Kohlrausch’s law.
Molar conductivity in a solution is the given conductance of a specific volume of a specific solution containing a single mole of ions held in the middle of two electrodes with the same cross-sectional area and the same distance between them at a certain concentration. The conduction of moles in a solution rises as the special concentration of a given solution decreases. This sudden increase in overall volume due to a single mole of the electrolyte increases the molar conductivity. The conductivity is called limiting or restraining molar conductivity, m°, as the concentration of electrolyte approaches zero.
While investigating the value of restricting molar conductivities of various electrolytes, Kohlrausch witnessed some special patterns. Kohlrausch argued that “a total of the specific contributions of the ions present in the electrolyte may be expressed as the molar conductivity of an electrolyte” as per his observations.
Kohlrausch’s Law Formula
The mole ratio conductivities of strong electrolytes at low concentration are described by the equation m=0m – Kc1/2, where m is the molar conductivity, 0m is the given molar conductivity (the molar conductivity in the limit of zero concentration when the ions do not interact), K is a coefficient related to the electrolyte’s stoichiometric ratio, and c is the electrolyte’s concentration. It is feasible to represent 0m as the total of each of its ions’ contributions.
Application of Kohlrausch’s Law
Determination of weak electrolytes: Extrapolation cannot be utilized to calculate the molar conductivity in a weak electrolyte at boundless dilution. Kohlrausch’s equation, on the other hand, may be used to calculate values for electrolytes with weak concentrations.
Determination of a weak electrolyte’s degree of ionization: At any concentration, Kohlrausch’s law may be used to decide the amount of ionization of a weak electrolyte. If the molar conductivity in an electrolyte that is weak at any concentration is C, and the molar conductivity regarding the specific electrolyte at infinite dilution is κ, then the degree at which the ionization occurs is then determined by,
:κ /c
The degree of ionization at any concentration may thus be estimated by knowing the values of κ and C from Kohlrausch’s equation.
The law gives a detailed description of the conductance of cations and anions in a given medium and hence is the basis of modern electrolysis. Calculating the average solubility regarding a sparingly soluble salt: A sparingly soluble salt has very low solubility in a solvent. Even a saturated solution of such a salt is so dilute that endless dilution can be assumed. The relationship may then be used to calculate the molar conductivity in a sparingly soluble salt at boundless dilution.
Conclusion
Friedrich Kohlrausch, a German physicist, researched several electrolyte solutions to establish their conductivity qualities between 1874 and 1879. It was said that he was examining the conductivity characteristics of electrolytes in order to figure out how they behaved and what kind of anomalies they had.
The ‘Kohlrausch’s Law of Migration or Independent Migration of Ions’ resulted from the study of the solutions. He named the ‘individual contribution’ of a particular ion to the total molar conductivity in an electrolyte as ‘Molar ionic conductivity’ after concluding that every ion in an electrolyte makes a ‘definite’ contribution to the complete molar conductivity (total molar conductivity) of given electrolyte at boundless dilution, regardless of the type of another ion in it. In 1876, he proposed the generalization law known as Kohlrausch’s law based on his findings.
