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Which freezes faster Tap water, distilled water or salt water? Would like some information on each to be able to show the difference in the three waters that would support which one would freeze first, second and third. Thank you!
Question Date: 2016-11-24
Answer 1:

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 salt water.

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 cold places.

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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