Question

How is cell constant determined?

Answer 1

The distance (l) between the electrodes and their area of cross-section (A) can be used to calculate the cell constant `(l/A)`. It is challenging to measure these numbers precisely, though. As a result, the value of the cell constant is ascertained indirectly.

Cell constant = `kappa/C`

i.e., Cell constant = `"Specific conductivity"/"Conductance"`

Therefore, the cell constant of the given cell can be found by measuring the conductance of a standard solution with known specific conductivity using the provided conductivity cell. For this purpose, usually an `N/50` KCl solution is used as the standard solution. This solution has a specific conductivity of 0.002765 ohm⁻¹ cm⁻¹ at 25°C. Thus, on using `N/50` KCl solution as the standard solution at 25°C, we have

Cell constant = `0.002765/("Conductance of" N/50 "KCl solution")`

or, Cell constant = 0.002765 × observed resistance of `N/50` KCl solution.