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Asked by IzzyClifton to Sarah, Sankar, Jo, Becky, Alan on 13 Mar 2015.
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Jo Sadler answered on 13 Mar 2015:
Adding salt lowers the melting point of ice, so that it stays a liquid down to lower temperatures. Obviously having liquid water on the road is much less dangerous than ice!
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Becky Gregory answered on 13 Mar 2015:
Salt lowers the freezing point of water, due to the addition of salt ions which form bonds with the water atoms. By adding salt to ice, it is able to dissolve in the liquid water within the ice, and hence melt the ice on the road.
Sometimes, however, if there is really thick ice on the road below a certain temperature, the salt cannot dissolve in the water around it and destruct the solid structure of the ice. In this case, sand is often spread over the ice, to provide a form of friction. (I saw this a lot when I lived and studied in Finland!)
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Sarah Kirk answered on 16 Mar 2015:
Salty water has a lower freezing point than normal water, so it melts the ice.
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Alan McCue answered on 16 Mar 2015:
Not much to add here other than we could lots of things other than salt to do this it just happens salt is fairly cheap and not very harmful!
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