If you put a cup of each type of water in your
freezer, the distilled water will freeze the
fastest. Whether tap water or salt water takes
second place will depend on how much stuff is in
the tap water compared to how much salt is in the
To understand why, let’s start with the
distilled water, since it probably has the least
amount of non-water molecules in it. We know that
this should freeze at 0 degrees Celsius (or 32
degrees Fahrenheit), forming a solid ice crystal
in the process. Now when we think about the other
two types of water, they have extra non-water
molecules like salt or other minerals in them.
These added molecules prefer being dissolved and
freely moving in liquid water rather than being
stuck in the crystal structure of solid ice. As a
result, they prevent freezing at the normal
temperature and you need to go to a lower
temperature (below 0 degrees Celsius) to freeze
the solution. This phenomenon is generally called
Freezing Point Depression. Antifreeze for
cars, which you or your parents might have heard
of, takes advantage of the same phenomenon to
prevent a car’s cooling system from freezing in
So if you believe this explanation, then you
can see why I can't tell for sure whether tap
water or salt water will freeze second fastest.
It's because I'm not sure how much stuff is in the
tap water compared to the salt water. Usually, the
more non-water molecules dissolved in your water,
then the lower the freezing temperature will get.
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