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The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). [1] The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 °C (27.3 °F). [2]
Workers spreading salt from a salt truck for deicing the road Freezing point depression is responsible for keeping ice cream soft below 0°C. [1]Freezing-point depression is a drop in the maximum temperature at which a substance freezes, caused when a smaller amount of another, non-volatile substance is added.
At 20 °C (68 °F) one liter of water can dissolve about 357 grams of salt, a concentration of 26.3 percent by weight (% w/w). At 100 °C (212 °F) (the boiling temperature of pure water), the amount of salt that can be dissolved in one liter of water increases to about 391 grams, a concentration of 28.1% w/w.
It is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is −21.1 °C (−6.0 °F) at the concentration of 23.3% NaCl by weight. [5]
However, the salt content of oceans lowers the freezing point by about 1.9 °C [41] (due to freezing-point depression of a solvent containing a solute) and lowers the temperature of the density maximum of water to the former freezing point at 0 °C.
Anything dissolved in water can have the same effect of lowering the freezing temperature, but salt is used, Ferguson says, because when one unit of salt dissolves, it yields two to three ...
As seawater freezes in the polar ocean, salt brine concentrates are expelled from the sea ice, creating a downward flow of dense, extremely cold, saline water, with a lower freezing point than the surrounding water. When this plume comes into contact with the neighboring ocean water, its extremely low temperature causes ice to instantly form ...
A bath of ice and water will maintain a temperature 0 °C, since the melting point of water is 0 °C. However, adding a salt such as sodium chloride will lower the temperature through the property of freezing-point depression. Although the exact temperature can be hard to control, the weight ratio of salt to ice influences the temperature: