Question

(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 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 MKCl` solution at `298 K` is `0.146 xx 10^(-3) S cm^(-1)`

Answer 1

(a). Molar conductivity`=` it is definied as the conducting power of all the ions produced by one gram mole of an electrolyte in solution it is denoted by `^^_(m)`
`^^_(m)=(k)/(C)xx1000Scm^(2)mol^(-1)`
where `k` is is electrlytic conductivity of solution and `C` is concentration of the solution expressed in `molL^(-1)` (or mol `dm^(-3))`
Variation of conductivity and molar conductivity with concentration.
In case of strong electrolyte, `^^_(m)` increase a little on dilution as shown in figure by straight line (decrease in conc.) because number of ions do not increase appreciable, only mobility of ions increase whereas in case of weak electrolyte, number of ions as weill as mobility of ions increase appreciable, therefore `^^_(m)` increase sharply as shown in the figure in form of curve.
Molar conductivity versus `C^(1//2)` for acetic acid (weak electrolyte) and potassium chloride (strong electrolyte) in aqueous solutions,
(b). `R=15000Omega,k=0.146xx10^(-3)Scm^(-1)`
`k=-(1)/(R)xx(l)/(A)implies(l)/(A)=kxxR=0.146xx10^(-3)Scm^(-1)xx1500ohm`
`implies(l)/(A)=219xx10^(-3)cm^(-1)=0.219cm^(-1)`