Equivalent Conductance 2 Measurement of Conductivity

The equivalent conductance is defined as the conductance of a solution containing 1 g equivalent of the dissolved electrol3de such that the entire solution is placed between two electrodes 1 cm apart. As direct determination of the quantity would need electrodes of enormous sizes, the equivalent conductance ( ,) is always evaluated through measurement of specific conductance or conductivity with the help of equation 1.2.8. 

Let the solution of the electrol3rte has a concentration of C g equivalent per litre then the volume of the solution containing 1 g equivalent would be 1000/C cubic centimetre.If this volume is imagined to be placed between two electrodes 1 cm apart, (Z = 1), the cross section of the column of solution or electrodes would be 1000/C sq. cm Hence equivalent conductance of the solution would be, 

An alternative unit, called molar conductance (Q) is defined as the conductance of a solution containing 1 g mole per litre, the solution being placed between two electrodes 1 cm apart. 

The specific conductance (L or K) or conductivity of a solution is always obtained by measuring the resistance (R) of the solution taken in a suitable container of known dimensions called conductivity cell, the cell constant of which has been determined by calibration with a solution of accurately known conductivity e g. a standard KCl solution. The instrument used for electrical conductivity measurement is known as conductivity bridge. A typical system consists of an alternating current (A.C.) Wheatstone bridge, a primary element of conductivity cell and a null balance indicator (as in solubridge ) or an electronic eye as in the conductivity meter. 

The passage of a current through a solution of an electrol3de may produce changes in the composition of the solution in the vicinity of the electrodes the potentials may thus arise at the electrodes with the consequent introduction of serious errors in the conductivity measurements unless such polarisation effects can be reduced to negligible proportions. These difficulties are 

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