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Conductance, Specific conductance and Molar conductance
One of the factors on which the conductance of an electrolytic solution depends is the concentration of the solution. In order to obtain comparable results for different electrolytes, it is necessary to take equivalent conductance's.
Equivalent conductance is defined as the conductance of all the ions produced by one gram equivalent of an electrolyte in a given solution. It is denoted by A.
To understand the manning of equivalent conductance, imagine a rectangular trough with two opposite sides made of metallic conductor (acting as electrodes) exactly 1 cm apart, If 1 cm3 (1 mL) solution containing 1 gram equivalent of an electrolyte is places in this container is measured.
According to definitions,
Conductance = Specific conductance (K)
= Equivalent conductance (A)
If the solution is diluted to say (9 cm3) (9 mL), the conductance of the solution will be the same but specific conductance becomes 1/9th as it contains nine cubes. The conductance is also equal to the equivalent because the solution still has 1 g equivalent of the electrolyte. This is shown in Fig. 12.3. Thus,
Equivalent conductance (A) = 9 × k
A = k × V ..... (v)
where V is the volume in mL containing 1 g equivalent of the electrolyte.
In case, if the concentration of the solution is c g equivalent per litre, then the volume containing 1 g equivalent of the electrolyte will be 1000/e.
So equivalent conductance
A = k × 1000/c ..... (vi)
A = k × 1000/N
where N = normality
The unit of equivalent conductance is ohm-1 cm-2 equi-1.