2021 ElectrochemistryKohlrausch's Law Medium Question 1 of 7 in Kohlrausch's Law

The molar conductance of NaCl, HCl and $CH_3COONa$ at infinite dilution are 126.45, 426.16 and 91.0 S cm$^2$ mol$^{-1}$ respectively. The molar conductance of $CH_3COOH$ at infinite dilution is. Choose the right option for your answer.

A $390.71\ S\ cm^2\ mol^{-1}$
B $698.28\ S\ cm^2\ mol^{-1}$
C $540.48\ S\ cm^2\ mol^{-1}$
D $201.28\ S\ cm^2\ mol^{-1}$

The answer is A.

Solution

By Kohlrausch's law: $\Lambda^\circ_{m(CH_3COOH)} = \Lambda^\circ_{m(CH_3COONa)} + \Lambda^\circ_{m(HCl)} - \Lambda^\circ_{m(NaCl)}$ $= 91.0 + 426.16 - 126.45 = 390.71\ S\ cm^2\ mol^{-1}$

Concept limiting molar conductivity of a weak electrolyte

Kohlrausch's Law in past papers

7 questions from this chapter have appeared across 6 exam years.