Question

What is the cell constant of a conductivity cell?

Answer 1

Hint: Conductivity is the amount of current carried between two electrodes by a known amount of liquid. The volume between the two electrodes must be precise or exact to determine the amount of current carried between them. This volume is known as cell constant.

Complete step by step answer:
The cell constant of a conductivity cell is the ratio of distance between the electrodes plates to the surface area of the electrode plates. It has unit $c{m^{ - 1}}$.It is represented by K. It is given as,-
$ \Rightarrow $ Cell constant=$\dfrac{{{\text{Distance between the electrodes}}}}{{{\text{Surface area of electrode plates}}}}$
Suppose the distance between the electrodes is ‘l’ and surface area is ‘a’ then cell constant K is given as-
$ \Rightarrow K = \dfrac{l}{a}$
This means that the solution having low conductivity has the electrodes placed together or have larger electrodes so that the cell constant remains less then one.
It is clear from the formula that the cell constant is only dependent on the distance between the electrodes and their surface area. It does not change with the following factors-
Temperature of electrolyte- there is no change with change in temperature.
Electrolytes-there is no change with change in electrolytes.
Concentration of electrolyte- there is no change with change in concentration of electrolytes.

Note:
We know that specific conductance is given as-
Specific conductance=conductance× $\dfrac{l}{a}$
Then Cell constant can be written as the ratio of specific conductance to Conductance (C).
$ \Rightarrow $ Cell constant$\left( {\dfrac{l}{a}} \right)$ =$\dfrac{{{\text{Specific conductance}}\left( {{\kappa }} \right)}}{{{\text{Conductance(C)}}}}$
Here specific conductance reciprocal of specific resistance given as-
$ \Rightarrow \kappa = \left( {\dfrac{{\text{1}}}{{{\rho }}}} \right)$ where ${{\rho }}$ is specific resistance and conductance is the ease with which current flows through electrolyte given as-
$ \Rightarrow C = \left( {\dfrac{1}{R}} \right)$ where R is Resistance.