What Happens When Salt Is Added to Boiling Water?

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Adding salt to boiling water increases the water's boiling point temperature. Adding any nonvolatile solvent, including salt, to a pure solvent increases its boiling temperature in a process scientists call boiling-point elevation. However, the elevation in this case is hardly noticeable, as it takes almost 4 tablespoons of salt to increase the boiling point of 1 quart of water by 1 degree.

A practical application of boiling point elevation is in the automobile radiator. A mixture of water and ethylene glycol increases the boiling point of the solution to prevent radiator boilover when the air conditioning is operating in the vehicle and ambient temperatures add to the engine's heat. In addition, ethylene glycol decreases the freezing point of the solution through freezing-point depression, which is why consumers often call it antifreeze. At the recommended 50-50 mix of antifreeze, the boiling point of water increases from 212 degrees Fahrenheit to 223 degrees Fahrenheit, according to HowStuffWorks. In addition, the freezing point of the solution drops to -32 degrees Fahrenheit.

In a vehicle, the heat from an engine easily raises the temperature of the water in the radiator to above the 223-degrees Fahrenheit point. In order to increase the boiling point even more, manufacturers install a closed cooling system that operates under pressure. By creating a system that operates at 15 pounds of pressure above atmospheric pressure, the boiling temperature of the coolant mix by another 45 degrees Fahrenheit, preventing most radiator boilover problems.