Question

(a) Apply Kohlrausch law of independent migration of ions, write the expression to determine the limiting molar conductivity of calcium chloride.
(b) Given are the conductivity and molar conductivity of NaCI solutions at 298 K at different concentrations :

Compare the variation of conductivity and molar conductivity of NaCI solutions on dilution. Give reason.
(c) 0.1 M KCI solution offered a resistance of 100 ohms in conductivity cell at 298 K. If the cell constant of the cell is `1.29 cm^(-1)`, calculate the molar conductivity of KCI solution.

Answer 1

(a) `wedge_(m(CaCI_(2)))^(@) = lambda_(Ca^(2+))^(0) + 2lambda_(CI^(-))^(0)`
(b) Conductivity of NaCI decreases on dilution as the number of ions per unit volume decreases.
Whereas, molar conductivity of NaCI increases on dilution as on dilution the interionic interacitons are overcome and ions are free to move.
(c) `G^(**) = kR`
`k = (1.29)/(100) = 0.0129 " S "cm^(-1)`
`wedge_(m) = (1000k)/(C)`
`wedge_(m) = (1000 xx 0.0129)/(0.1)`
`wedge_(m) = 129" S " cm^(2)mol^(-1)`