Conductivity (electrolytic)

[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 This corresponds to a specific resistivity of The preparation of salt solutions often takes place in unsealed beakers.

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.

The commonly used standard cell has a width of 1 cm[clarify], and thus for very pure water in equilibrium with air would have a resistance of about 106 ohms, known as a megohm.

The conversion of conductivity (in μS/cm) to the total dissolved solids (in mg/kg) depends on the chemical composition of the sample and can vary between 0.54 and 0.96.

Typically, the conversion is done assuming that the solid is sodium chloride; 1 μS/cm is then equivalent to about 0.64 mg of NaCl per kg of water.

Electrolytic conductivity is highly temperature-dependent, but many commercial systems offer automatic temperature correction.

This quotient, termed molar conductivity, is denoted by Λm: Strong electrolytes are hypothesized to dissociate completely in solution.

A weak electrolyte is one that is never fully dissociated (there is a mixture of ions and neutral molecules in equilibrium).

For a monoprotic acid HA obeying the inverse square root law, with a dissociation constant Ka, an explicit expression for the conductivity as a function of concentration c, known as Ostwald's dilution law, can be obtained: Various solvents exhibit the same dissociation if the ratio of relative permittivities equals the ratio cubic roots of concentrations of the electrolytes (Walden's rule).

The reason for this is that as concentration increases the average distance between cation and anion decreases, so that there is more interactions between close ions.

So an "ion-association" constant K can be derived for the association equilibrium between ions A+ and B−: Davies describes the results of such calculations in great detail, but states that K should not necessarily be thought of as a true equilibrium constant, rather, the inclusion of an "ion-association" term is useful in extending the range of good agreement between theory and experimental conductivity data.

[16] The existence of a so-called conductance minimum in solvents having the relative permittivity under 60 has proved to be a controversial subject as regards interpretation.

Basic compensation is normally done by assuming a linear increase of conductivity versus temperature of typically 2% per kelvin.

The change in conductivity due to the isotope effect for deuterated electrolytes is sizable.

This type of measurement is not ion-specific; it can sometimes be used to determine the amount of total dissolved solids (TDS) if the composition of the solution and its conductivity behavior are known.

Sometimes, conductivity measurements are linked with other methods to increase the sensitivity of detection of specific types of ions.

[35] The electronic conductivity of purified distilled water in electrochemical laboratory settings at room temperature is often between 0.05 and 1 μS/cm.

Environmental influences during the preparation of salt solutions as gas absorption due to storing the water in an unsealed beaker may immediately increase the conductivity from 0.055 μS/cm and lead to values between 0.5 and 1 μS/cm.