Conductance in electrolytic solutions
Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m).
Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring the ionic content in a solution.
The SI unit of conductivity is S/m and, unless otherwise qualified, it refers to 25 °C.
Often encountered in industry is the traditional unit of μS/cm. 106 μS/cm = 103 mS/cm = 1 S/cm.
The values in μS/cm are lower than those in μS/m by a factor of 100 (i.e., 1 μS/cm = 100 μS/m).
Sometimes encountered is mho (reciprocal of ohm): 1 mho/m = 1 S/m.
Historically, mhos antedate Siemens by many decades; good vacuum-tube testers, for instance, gave transconductance readings in micromhos.
Resistance, R, is proportional to the distance, l, between the electrodes and is inversely proportional to the cross-sectional area of the sample, A (noted S on the Figure above). Writing ρ (rho) for the specific resistance .
R = I / A * p
In practice the conductivity cell is calibrated by using solutions of known specific resistance, ρ*, so the quantities l and A need not be known precisely
R* = C*P*
The specific conductance, κ (kappa) is the reciprocal of the specific resistance.
k = 1 / ρ = C / R
Conductance = Specific conductance (K) = Equivalent conductance ( λ)
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.
Equivalent conductance (λ ) = 9 × k
λ = k × V
where V is the volume in mL containing 1 g equivalent of the electrolyte.