Question

Define molar conductivity.

Hint:

Molar conductivity is the conductance of a solution with 1 mole of electrolyte between electrodes 1 cm apart, equal to 1000 times kappa divided by molarity.

Answer 1

Step 1: Start with conductivity:
The conductivity (\( \kappa \)) of a solution is the conductance of a one-metre cube (or one cm cube) of that solution.
It depends on how many ions are present in the cube.
So it changes when we dilute the solution.

Step 2: Define molar conductivity:
Molar conductivity (\( \Lambda_m \)) is the conductance of a solution that contains one mole of the electrolyte.
The solution is placed between two parallel electrodes that are 1 cm apart.
The electrodes are large enough to hold the whole solution between them.

Step 3: Write the relation:
If \( c \) is the concentration in mol per litre and \( \kappa \) is in S per cm, then
\[ \Lambda_m = \frac{\kappa \times 1000}{c} \]
Its unit is \( \mathrm{S\ cm^2\ mol^{-1}} \).

Final Answer:
Molar conductivity is the conductance of the solution containing 1 mole of electrolyte placed between two electrodes 1 cm apart. \[ \boxed{\Lambda_m = \frac{\kappa \times 1000}{c}} \]