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We typed "how does salt melt ice" into the Yahoo! Search box and were soon traveling the well-worn path to How Stuff Works. There we learned that the answer has to do with melting points. Most people know that water freezes at a temperature of 32°Fahrenheit (0°Celsius). Salt dissolves fairly rapidly in ice, lowering its freezing point in an effect known as freezing point depression, and melting it in the process. But what's going on at the molecular level? Basically, salt molecules
are bonding with water molecules, making it more difficult for ice to form. The result is a solution with a lower freezing temperature. For example, a 10% salt solution freezes at 20°F (-6°C), while a 20% salt solution freezes at 2°F (-16°C). You've also probably noticed the effect of salt water on freezing points if you've tried to make ice cream or if you've wondered why the ocean doesn't freeze at the same time as bodies of fresh water, such as rivers, lakes, and ponds.
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