Conductivity (electrolytic)

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.^[1] For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems.

In many cases, conductivity is linked directly to the total dissolved solids (TDS).

High quality deionized water has a conductivity of
${\displaystyle \mathrm {\kappa \;=\;0.05501\,\pm \,0.0001\,{\frac {\mu S}{cm}}} }$ at 25 °C.
This corresponds to a specific resistivity of
${\displaystyle \rho \,=\,18.18\pm 0.03\;\mathrm {M\Omega \cdot cm} }$.^[2]
The preparation of salt solutions often takes place in unsealed beakers. In this case the conductivity of purified water often is 10 to 20 times higher. A discussion can be found below.

Typical drinking water is in the range of 200–800 μS/cm, while sea water is about 50 mS/cm^[3] (or 0.05 S/cm).

Conductivity is traditionally determined by connecting the electrolyte in a Wheatstone bridge. Dilute solutions follow Kohlrausch's law of concentration dependence and additivity of ionic contributions. Lars Onsager gave a theoretical explanation of Kohlrausch's law by extending Debye–Hückel theory.