How Does Salt Affect the Boiling Point of Water?

The purpose of this experiment was to determine whether or not salt would affect the boiling point of water. Much of the research I conducted rejected my hypothesis which stated: if I add salt to water, then the boiling point of the water will decrease. Factors such as colligative properties determine how a solvent will behave once it becomes a solution (Bradley, 2006). Much of the research involved used boiling point elevation as a method to explain why the boiling point of water is affected by salt. Although my hypothesis was refuted, the research allowed me to understand the actual reason for the use of salt while cooking and it also helped to answer my question of how salt helps food cook faster.

How Does Salt Affect the Boiling Point of Water?
As a child, I was always told that adding a pinch of salt to water while cooking will help the food cook faster. This is what led me to ask the question: How does adding salt to water help make the food cook faster? Maybe it had something to do with the boiling point of the water. I assumed that if the food was able to cook faster it was because the boiling point of the water was lowered and that the water was able to boil at a faster rate. Thus, I created a hypothesis: If I add salt to water, then the boiling point of the water will decrease.

However, there was much evidence that proved this to be otherwise. Adding salt to water actually increases the boiling point of water, a phenomena known as boiling point elevation. Boiling point elevation is a colligative property, which are properties of solutions that depend on the number of dissolved particles in the solution, but not on the identities of the solutes (Bradley, 2006). Boiling point elevation occurs when the boiling point of a solution becomes higher than the boiling point of a pure solvent (Helmenstine, 2012). Basically, water is known as a solvent and salt is known as a non-volatile solute. When you add salt to water, it makes water become an impure solvent and raises its boiling point above that of the pure solvent (Action Donation Services, 2006). The boiling point of water rises if you add salt to it, but only by about 2°C to 102°C (Southwest Research Institute, 2012). As soon as any of the salt dissolves in the water, the boiling point of the water will begin to rise by about one half degree Celsius for every 58 grams of salt dissolved per kilogram of water (Yahoo! Answers, 2012).

Conclusion

To recap, salt raises the boiling temperature of water, but only by a small degree. However, it is used in cooking because adding salt to water makes the water hotter, not boil faster (Maureen, 2010). The greater boiling temperature will allow foods such as noodles and potatoes to cook faster and more thoroughly (Chen, 2013). This fact most likely led to the misconception that salt lowers the boiling point of water which makes it boil faster, however, this is incorrect.

References

Helmenstine, A. M. (2012). Does adding salt lower the boiling point of water?. Retrieved from http://chemistry.about.com/od/foodchemistryfaqs/f/Does-Adding-Salt-Lower-The-Boiling-Point-Of-Water.htm Helmenstine, A. M. (2012). Boiling point elevation: What boiling point elevation is and how it works. Retrieved from http://chemistry.about.com/od/solutionsmixtures/a/boilingpointele.-NxZ.htm Bradley, D. (2006, December 27). Salt and the boiling point of water.