Investigation of the effect of NaCl concentration on the evaporation rate of water.
Chemistry HL Internal Assessment
Vitaebella Tsang Ao Ling
Contents page
Contents page 2
Introduction 3
Design 4
Research question 4
Variables 4
Method 5
Results 6
Discussion 9
Evaluation 9
Bibliography 10
Introduction
Many recipes call for salt to be added to the water when cooking pasta to add flavor, but there has been common belief or misunderstanding that adding salt will make the water boil faster. However, it is now known that that is not the fact, and that adding salt will do the opposite and make the water boil more slowly instead. The boiling point of saltwater is higher than pure water, so it takes longer for saltwater to reach its boiling point and for all the water to boil and evaporate completely. This phenomenon is known as boiling-point elevation.
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The boiling point of the solution will be higher than that of the pure solvent itself. The boiling point of a liquid is the temperature at which its vapor pressure is to equal the atmospheric pressure. When a solute is added there are less solvent molecules near the surface and the solvent’s vapor pressure will decrease, so the vapor pressure of the solution will be less than that of the solvent. For the vapor pressure to reach the atmospheric pressure, a higher temperature must be reached, which means the boiling point is elevated. According to this theory, adding salt to water would make the boiling point higher, and make it harder to reach the boiling point.
The boiling-point elevation can be calculated by this