This winter has been filled with so much rain and snow. I started wondering what the difference is between the salt they place on icy roads and the salt you use to make homemade ice cream?
Is it the same kind of salt? What does the salt on the road do? Does it help with friction or melt the ice?
I thought the salt mixed with ice, to make ice cream, makes the freeze temperature lower?
I’m confused…
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Mixing in salt (of any kind) does indeed lower the temperature water freezes at. On roads, that’s helpful because it means that the road won’t freeze and get icy until it’s colder outside.
For ice cream, that’s helpful because of how the process of melting works. When something is melting (this is true for any solid, not just ice/water), it takes heat to break apart the solid structure into a liquid in addition to the heat it takes to warm it up. The solid can’t get any hotter than the melting point, because it can’t do that and stay solid, so it also keeps the liquid cool while it melts. This means that a partially-melted mixture will always stay at the freezing temperature. Once the ice all melts, it’ll warm up normally again. Making ice cream works better if you can keep it at a temperature that’s colder than the normal freezing temperature of water, and if you put in just ice, it’s going to become an ice/water mixture pretty fast. So, if you want to keep your soon-to-be ice cream at a temperature that is colder than the temperature water freezes at, you need to have ice that melts at lower than the usual temperature, which you achieve by adding salt.
You *can* use the exact same salt on roads and to make ice cream, but in practice they’re typically different. People use table salt for ice cream because if you’re cooking you probably already have it around. They use a variety of different salts on roads because they have different properties that give them different abilities to stick to the road, not harm the local environment, and have different prices.
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