posted by meg .
how much salt must I put into a 100mls of water to stop it freezing when left overnight in a home freezer
That depends upon the temperature setting of your freezer. It is adjustable, you know. A recommended setting is 0 F (-18 C)
I suggest you calculate the freezing point depression of a fully saturated solution of NaCl. That will tell you how high the temperature setting will have to be, to prevent freezing.
It turns out that you can reduce the freezing point to as low as -21 C with a fully saturate salf solution.
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