Kohlrausch's Law

[ I ] The relationship between the concentration of a strong electrolyte in a dilute solution and the equivalent electrical conductivity is an empirical law discovered experimentally by FWG Kohlrausch. If the equivalent electrical conductivity at infinite dilution ^is Λ∞ , the equivalent electrical conductivity Λ at a concentration c (molar concentration) can be expressed as follows:

Λ ＝ Λ ^∞ － A

Here, A is a constant determined by the temperature, solvent, and type of electrolyte. This equation is called the square root law because Λ is linearly related to , and was later theoretically derived by L. Onsager (Onsager's equation). However, when the concentration is 0.001 mol L ^-1 or more, the measured value of Λ deviates from the above equation, so a semi-empirical equation has been proposed that adds a correction term to match the measured value as closely as possible. [ II ] In an infinitely dilute solution, the value of equivalent ionic conductivity is determined only by the properties of the solvent (temperature, pressure, viscosity, etc.) and the properties of the ions themselves, regardless of the types of coexisting ions. Therefore, this law, which was experimentally confirmed by Kohlrausch, states that the equivalent electrical conductivity of an electrolyte under infinitely dilute conditions is given by the sum of the equivalent ionic conductivities of the ions that make up the electrolyte. It is also called Kohlrausch's additivity law or the law of independent movement of ions.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

【Ⅰ】希薄溶液中における強電解質の濃度と当量電気伝導率との間の関係で，F.W.G. Kohlrauschにより実験的に見いだされた経験則．濃度c(モル濃度)における当量電気伝導率Λは，無限希釈における当量電気伝導率を Λ^∞ とすると，次のように表される．

Λ ＝ Λ^∞ － A

ここで，Aは温度，溶媒と電解質の種類により決まる定数である．この関係式は，Λがと直線関係にあるので平方根則とよばれ，のちに，L. Onsager(オンサガー)により理論的に導き出された(オンサガーの式)．なお，濃度が0.001 mol L^－1 以上になると，Λの実測値は上式よりはずれてくるので，実測値とできるだけ合うように補正項を加えた半実験式も提出されている．【Ⅱ】無限希釈溶液中では，当量イオン伝導率の値は，共存するイオンの種類には無関係に，溶媒の性質(温度，圧力，粘度など)とそのイオン自身の性質だけで定まり，したがって，無限希釈の状態下での電解質の当量電気伝導率は，電解質を構成するイオンの当量イオン伝導率の総和で与えられるという，Kohlrauschにより実験的に確かめられた法則．コールラウシュの加成則あるいはイオン独立移動の法則ともよばれる．

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