Does Adding Salt Lower the Boiling Point of Water?

Does adding salt lower the boiling point of water? You may have heard this and wondered if it was true. Here is a look at the science behind salt and boiling water.

Effect of Salt on Boiling Water

Adding salt does not lower the boiling point of water. Actually, the opposite is true. Adding salt to water results in a phenomenon called boiling point elevation. The boiling point of water is increased slightly, but not enough that you would notice the temperature difference. The usual boiling point of water is 100 °C or 212 °F at 1 atmosphere of pressure (at sea level). You would have to add 58 grams of salt just to raise the boiling point of a liter of water by one half of a degree Celsius. Basically, the amount of salt people add to water for cooking doesn't affect the boiling point at all.

Why does salt affect boiling point? Salt is sodium chloride, which is an ionic compound that breaks apart into its component ions in water. The ions floating around in the water alter how the molecules interact with each other. The effect isn't restricted to salt. Adding any other compound to water (or any liquid) increases its boiling point.

Salt in Water Safety Tip

If you add salt to water, be sure to add it before boiling the water. Adding salt to water that is already boiling may cause the water to splash up and boil more vigorously for a few seconds.

Source

• Atkins, P. W. (1994). Physical Chemistry (4th ed.). Oxford University Press. ISBN 0-19-269042-6.