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Why does salt melt ice?

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posted Aug 29, 2017 by Jordan White

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2 Answers

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Salt melts ice essentially because adding salt lowers the freezing point of the water. How does this melt ice? Well, it doesn't, unless there is a little water available with the ice.
The good news is you don't need a pool of water to achieve the effect. Ice typically is coated with a thin film of liquid water, which is all it takes for the salt to work.
Pure water freezes at 32 F (0 C). Water with salt (or any other substance in it) will freeze at some lower temperature. Just how low this temperature will be depends on the de-icing agent. If you put salt on ice in a situation where the temperature will never get up to the new freezing point of the salt-water solution, you won't see any benefit. For example, tossing table salt (sodium chloride) onto ice when it's 0 F won't do anything more than coat the ice with a layer of salt. On the other hand, if you put the same salt on ice at 15 F, the salt will be able to prevent melting ice from re-freezing. Magnesium chloride works down to 5 F while calcium chloride works down to -20 F.

answer Aug 30, 2017 by Willow Wilson
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Salt Lowers the Freezing Point. In a nutshell, salt is a great ice melter because it causes “freezing point depression.” This means that salt helps in lowering the freezing point and, consequently, the melting point of water (the main component of snow and ice).

answer Aug 30, 2017 by Shivaranjini
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