Saline water

Saline water, also known as salt water, is water that contains a lot of dissolved salts, mostly sodium chloride. It is saltier than brackish water but not as salty as brine. Scientists measure how salty water is using parts per thousand or parts per million.

There are different levels of saline water. Slightly saline water has 1,000 to 3,000 parts per million of salt. Moderately saline water has 3,000 to 10,000 parts per million, and highly saline water has 10,000 to 35,000 parts per million. Seawater is highly saline, with about 35,000 parts per million of salt.

The amount of salt that can dissolve in water changes a little with temperature. At 20 °C, one liter of water can dissolve about 357 grams of salt. At 100 °C, it can dissolve about 391 grams. This tells us how much salt water can hold under different conditions.

Properties

Saline water, also called salt water, contains a lot of dissolved salts, mostly sodium chloride. It is saltier than brackish water but not as salty as brine. The amount of salt is measured in parts per thousand (permille, ‰) and parts per million (ppm).

At 100 °C, saturated sodium chloride brine is about 28% salt by weight. At 0 °C, brine can only hold about 26% salt. At 20 °C, one liter of water can dissolve about 357 grams of salt.

The thermal conductivity of seawater (3.5% dissolved salt by weight) is 0.6 W/mK at 25 °C. The thermal conductivity changes with salinity and temperature. The salt content can be measured with a salinometer.

The density of brine at different concentrations and temperatures can be calculated using a special equation.

Electrolysis

A small amount of hydrogen gas is made by electrolysis. This hydrogen is usually a by-product when making chlorine.

• 2 NaCl(aq) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g) + Cl₂(g)