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Why does salt melt ice?

Salt lowers the freezing point of water.
Ice melts faster when salt is added as the salt lowers the freezing point of the ice, this is known as freezing point depression. The more salt you add the lower the freezing point.
This interesting feature of salt and ice and can be used for lots of fun and easy experiments.

Making ice cream with ice and salt

Did you know you can make ice cream using milk, salt and ice?
This works because as the ice melts heat is absorbed from the surroundings ( the milk mixture ) making them freeze.
Did you know you can make your own ice cream in less than 10 minutes with just milk, salt and ice?
How to make ice cream with ice and salt
Materials
A large bag of ice
Salt
Milk – we used chocolate milk
A tablespoon sugar and a tea spoon vanilla essence – options. 
Method
Pour about a cup of milk into a ziploc bag, add the sugar and vanilla essence ( or just use flavoured milk ). Make sure this bag is properly sealed.
Half fill a bigger ziploc bag with ice and add a good amount of salt.
Put your milk bag into the ice bag and give it a good shake.
Try and keep the milk in contact with the ice as much as possible.
Keep rolling the ice over the milk, you should feel the ice in the bag get VERY cold, so might need to put a towel around the bag.
Check the milk after 5 minutes, it should be a similar consistency to ice cream, but if not keep going for a bit longer. 
Why does this happen?
When salt it mixed with ice it makes the ice melt as it lowers the freezing point of the ice, this is known as freezing point depression. The more salt you add the lower the freezing point. For the ice to melt heat must be absorbed from the surroundings ( in this case the milk mixture ) causing it to freeze.
You should find the ice feels extra cold, which is why you’ll need a towel to cover the bag after a  few minutes.
Practical applications
During cold weather salt and grit are applied to roads, the salt makes the ice melt even if the air temperature is below freezing point.
Extension ideas
Do you think a solution of ice and salt would freeze in a normal freezer?
Watch our video here:

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