Sodium chloride is used to clear snow on roads. It is also used in ice creams I.e. to keep it solid. Why?
Sodium chloride or salt is used to clear snow on roads and is also used in ice creams i.e. to keep it solid. In both the cases, the salt works by lowering the melting or freezing point of water.
Salt melts ice by lowering the freezing point of the water around the ice. The ice melts because we are introducing dissolved foreign particles into the water. The freezing point of water becomes lower and this is called freezing point depression. The ice is unable to re-freeze except at a much lower temperature.
Now, in case of ice cream when salt is added to ice that surrounds a container with the liquid ice cream mixture, the freezing point of the ice drops and it begins to melt. This transfers heat from the surrounding environment that freezes the ice cream.