Experimental methods of determining electrolytic conductivity

The electrolyte conductivity can be measured using a conductivity cell which consists of a pair (or pairs) of electrode(s) of known area separated by a constant distance. A simple two-electrode cell can be used. For small excursions of potential, the current response of the cell is proportional to the electrolytic conductance, L. The conductivity, k (see equation (20.1.2-3)) is related to L via (4, 9) 

The essential point with regard to the interpretation of data is that the molar conductivity (see equation (20.1.2-10)) at infinite dilution can be broken down into terms due to the constituent ions. Some knowledge of the transference properties of the individual ions can be used to determine the fraction of electrolyte conductivity attributable to each ion. 

To illustrate the relation between transference numbers and conductivity, the transport number of potassium in dilute potassium chloride solution is used to find the limiting ionic conductivity. On extrapolation to infinite dilution, the molar conductivity of aqueous potassium chloride solution is found to be 149.85 S cm moE (11). From equation (20.1.2-14) and the value for found in Section 20.2.3  

The remaining molar conductivity of the potassium chloride solution can be attributed to the chloride anion if one neglects the contribution arising from the auto-ionisation of water. Hence, the limiting ionic conductivity of the chloride anion is 76.42 S cm moE.  

The values of individual ionic conductivities can also be found by comparison between the extrapolated values. For example, the limiting molar conductivity of magnesium chloride is found to be 258.7 S cm moE. Comparison with the potassium chloride value yields the limiting ionic conductivity of magnesium  

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