How would you measure the conductivity of ionic solutions?

Explanation

(i) The conductivity of an electrolytic solution is determined by using a wheatstone bridge arrangement in which one resistance is is replaced by a conductivity cell filled with the electrolytic solution of unknown conductivity.
(ii) In the measurement of specific resistance of a metallic wire, a DC power supply is used. Here AC is used for this measurement to prevent electrolysis. Because DC current through the conductivity cell leads to the electrolysis of the solution taken in the cell.
(iii) A wheatstone bridge is consitituted using known resistance P,Q, a variable resistance S and conductivity cell. An AC source (550 Hz to 5 KHz) is connected between the junctions A and C. A suitable detector is connected between the junction B and D.
(iv) The variable resistance S is adjusted until the bridge is balanced and in this conditions, there is not current flow through the dectector.
(v) Under balanced condition
`P//Q = R//S`
`:. R = P//Q xx S " " ...........(1)`
The resistance of the electrolytic solution (R ) is calculated from the known resistance values, P,Q and measured S value using the equation (1).
(vi) Specific conductance (or) conductivity of an electrolyte can be calculated from the resistance value (R ) using the following expression
`k = 1/R [l/A]`
(vii) The value of cell constant `l/A` is usually provided by the cell manufacturer. Alternatively the cell constant may be determined using KCl solution whose concentration and specific conductance are known.