(a) Define molar conductivity of a solution and explain how molar conductivity changes with change in concentration of solution for a weak and a strong electrolyte.
(b) The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is `1500 Omega`. What is the cell constant if the conductivity of 0.001 M KCl solution at 298 K is `0.146 xx 10^(-3) S cm^(-1)`?

Explanation

(a) Molar conductivity is the conductivity of all the ions produced by ionisation of 1 g mol of an electrolyte when present in V mL of solution. It is denoted by `Lambda_(m)`.
where V = volume in mL containing 1 g mol of the electrolyte
`Lambda_(m) = k xx 1000/C`
where C = concentration of the solution in g mol/L.
Variation of molar conductivity with concentration for strong electrolytes - Molar conductivity increases slowly with dilution. It approaches a limiting value when the concentration approaches zero. This value is called molar conductivity at infinite dilution `Lambda_(m)^(@)`. Variation of conductivity with concentration may be given by:
`Lambda_(m)= Lambda_(m)^(@) =AC^(1//2)`, where A is a constant and C is concentration.
Variation of molar conductivity with concentration for weak electrolytes - Variation of `Lambda_(m)` with concentration is very large to the extent that we cannot obtain molar conductance at infinite dilution `Lambda_(m)^(@)` by extrapolation of `Lambda_(m)` vs `C^(1//2)` plots.
(b) Conductivity `K = 0.146 xx 10^(-3) S cm^(-1)`
Resistance = R= 1500 ohm
Cell constant = Conductivity (k) `xx` Resistance (R)
`=0.146 xx 10^(-3) S cm^(-1) xx 1500 Omega`
`=0.219 cm^(-1)`