A student asked me this today. I understand that salt doesn’t actually melt ice, but lowers its melting temp, but how do I explain this to a child?
In: 3
It freezes ice cream because sugar, along with salt, decreases the freezing point of water. Therefore, to properly freeze a sugary water substance (ice cream), you need a temperature below the freezing point of pure water. Salt is used in ice cream machines because most homeowners don’t have a freezer large enough to fit an ice cream churn inside and that is the only way to effectively reach temperatures that would solidify a sugary water substance (ice cream). Salt melts ice ONLY when it is above the freezing point of salt water (also, most ice melting salt is not just normal sodium chloride). It just happens that many places on Earth do not get below the freezing point of saturated salt water for extended periods of time.
Edit: No one has pointed out that you actually need temperatures far below the freezing point of water to freeze ice cream. Commerical ice cream production doesn’t typically use salt water to freeze ice cream because they have specialized devices that can get colder then the freezing point of water to freeze the ice cream (typically glycol chillers).
Latest Answers