More Info: A pinch of salt added into a pan of water being brought to boil will have little effect on the time it takes to reach the vaporizing point. However, if the quantity of salt used is at all larger, it can actually mean that it will take longer for the water to reach its boiling point.
The Colligative Properties
The principle at work is something chemists refer to as colligative properties. Salt is the solvent, and water is the solution. If the solvent added to the solution has a lower boiling point than the solution, it can help lower the overall boiling threshold and thus bring the solution to boil faster. If, on the other hand, the solvent has a higher boiling point than the solution, as is the case of salt to water, then it will raise the overall boiling threshold and make water boil slower.
The impact that salt can have on water’s freezing point is the reason why it is also used on snow-covered roads. Just as a certain amount of salt will raise the boiling point of water, a sufficient amount of salt spread onto icy or slushy roads will lower the freezing point, thus delaying the transformation of wet roads into slick, icy surfaces.
Freezing point depression, like boiling point elevation, is another colligative property. Ultimately, adding one or more solvents to a solution almost always raises the boiling point or lowers the freezing point. The real issue is the quantity of additional components that is being added, as this will further impact the change in boiling or freezing tipping points.
Seasoning a pan of boiling water with a pinch of salt is one thing; but if the cap pops off the saltshaker and a large amount of salt falls into the water, dinner guests may have to wait a little longer for the main course to be served.
Sciencebase.com – “Salt and the Boiling Point of Water”, December 27, 2006, Retrieved August 23, 2010 from http://www.sciencebase.com/science-blog/how-does-salt-affect-the-boiling-point-of-water.html
“Freezing Point Depression in Solutions.” Hyperphysics. N.p., n.d. Web. 24 Aug. 2010. http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/meltpt.html.
“colligative.” Department of Chemistry. Iowa State University, n.d. Web. 24 Aug. 2010. <http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html>.