Why does salt water boil faster than plain water?
You better read the following site:
http://www.newton.dep.anl.gov/askasci/gen01/gen01021.htm
To explain why salt water boils faster than plain water, we need to understand the concept of boiling point elevation.
Boiling is the process by which a liquid turns into a vapor when its vapor pressure equals the atmospheric pressure. The boiling point of a liquid is the temperature at which this occurs.
When salt, or any solute, is added to water, it disrupts the regular arrangement of water molecules, reducing their ability to escape into the gas phase. As a result, salt water requires more energy (heat) to reach the same vapor pressure as plain water.
The phenomenon of boiling point elevation occurs because the dissolved salt particles create a higher boiling point for the water. This means that salt water needs to be heated to a higher temperature than plain water in order to boil.
You can see this effect in everyday cooking. For example, when you cook pasta in salted water, the higher boiling point of the salted water can help the pasta cook faster than if it was cooked in plain water.