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. 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
- μS/cm at 25 °C.
This corresponds to a specific resistivity of
- MΩ⋅cm.
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 (or 0.05 S/cm).
Electrolytic conductivity varies from about 10E-10 S/m for purified toluene up to about 10 S/m for recently discovered highly concentrated “water-in-salt” solutions.
Conductivity of aqueous and other polar solutions 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.
Conductivity of low- and non-polar solutions is very low and usually measured with probes having high cell constant and applying low frequency electric field.