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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).
The Bresle method uses the difference of conductivity of salts in water, each salt having a characteristic conductivity-versus-concentration relationship. The correlation between concentration and conductivity can be found in "Handbook of Chemistry and Physics". This relationship is useful only if the dissolved salt is known.
Electrical conductivity of water samples is used as an indicator of how salt-free, ion-free, or impurity-free the sample is; the purer the water, the lower the conductivity (the higher the resistivity). Conductivity measurements in water are often reported as specific conductance, relative to the conductivity of pure water at 25 °C.
The plate distance is one centimeter, the special conductivity values were calculated from the Lasance approximation formula in The Thermal conductivity of Air at Reduced Pressures and Length Scales [28] and the primary values were taken from Weast at the normal pressure tables in the CRC handbook on page E2. [27]
A river or lake water with a salinity of around 70 mg/L will typically have a specific conductivity at 25 °C of between 80 and 130 μS/cm. The actual ratio depends on the ions present. [14] The actual conductivity usually changes by about 2% per degree Celsius, so the measured conductivity at 5 °C might only be in the range of 50–80 μS/cm.
In the technical terms of physical chemistry, the minimum freezing point of a water-salt mixture is −21.12 °C (−6.02 °F) for 23.31 wt% of salt. Freezing near this concentration is however so slow that the eutectic point of −22.4 °C (−8.3 °F) can be reached with about 25 wt% of salt.
This conductivity gain upon dissolving or melting is sometimes used as a defining characteristic of salts. [76] In some unusual salts: fast-ion conductors, and ionic glasses, [53] one or more of the ionic components has a significant mobility, allowing conductivity even while the material as a whole remains solid. [77]
The effect is commonly seen as an effect on the solubility of salts and other weak electrolytes. Adding an additional amount of one of the ions of the salt generally leads to increased precipitation of the salt, which reduces the concentration of both ions of the salt until the solubility equilibrium is reached. The effect is based on the fact ...