Name: Problem on Kohlrausch's Law
Uploaded: 2019-07-19
Duration: 24 min 21 s
Description: Kohlrausch's law is used to determine the total conductance offered by the electrolyte at infinite dilution. Watch the video and understand the problem based...

Question

State and explain Kohlrausch's law of independent migration of ions. The equivalent conductance at infinite dilution

\land_{eq}^{\infty}

for sodium acetate, sodium chloride, and hydrochloric acid are

78

,

109

and

384 {Ohm}^{- 1} {cm}^{2} g . {eq}^{- 1}

respectively. Calculate

\land_{eq}^{\infty}

acetic acid.

Accepted Answer

The individual contribution of an ion towards the total equivalent conductivity of the electrolyte is called the equivalent ionic conductivity. On the basis of this, Kohlrausch's gave a law that is known as Kolrausch's law of independent migration of ions. According to this law, the equivalent conductance of an electrolyte at infinite dilution can be expressed as the sum of the equivalent conductance of cations and anions at infinite dilution. For example, the equivalent conductance of sodium chloride $(NaCl)$ at infinite dilution is equal to the sum of the equivalent conductance of sodium ion and chloride ion at infinite dilution. This can be expressed as:

$\land_{eq (NaCl)}^{\infty} = λ_{{Na}^{+}}^{\infty} + λ_{{Cl}^{-}}^{\infty}$

Given:

The equivalent conductance of sodium chloride at infinite dilution $\land_{eq (NaCl)}^{\infty} = 109 {Ohm}^{- 1} {cm}^{2} g . {eq}^{- 1}$

The equivalent conductance of sodium acetate at infinite dilution $\land_{eq ({CH}_{3} COONa)}^{\infty} = 78 {Ohm}^{- 1} {cm}^{2} g . {eq}^{- 1}$

The equivalent conductance of Hydrochloric acid at infinite dilution $\land_{eq (HCl)}^{\infty} = 384 {Ohm}^{- 1} {cm}^{2} g . {eq}^{- 1}$

According to Kolrausch's law, the equivalent conductance of a weak electrolyte can be determined by the help of the equivalent conductivities of strong electrolytes.

So, $\land_{eq ({CH}_{3} COOH)}^{\infty} = \land_{eq ({CH}_{3} COONa)}^{\infty} + \land_{eq (HCl)}^{\infty} - \land_{eq (NaCl)}^{\infty}$

$= 78 + 384 - 109 = 353 S {cm}^{2} g . {eq}^{- 1}$

Hence, the equivalent conductance of acetic acid at infinite dilution is $353 S {cm}^{2} g . {eq}^{- 1}$ .

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