15.11 Introduction to the Vapor Pressure of a Solution (Raoult’s Law) (Video)
- Page ID
- 342522
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Video Topics
The methods for calculating the vapor pressure of a solution are dependent on the characteristics of the solute. A nonionic-nonvolatile solute will cause the vapor pressure of the solvent to decrease. Because the solute is nonvolatile it will not create a vapor pressure of its own. Examples are: sugar, caffeine, fats, and proteins. An ionic-nonvolatile solute will also cause the vapor pressure of the solvent to decrease. Because the solute is nonvolatile it will not create a vapor pressure of its own. However, we will need to adjust our calculations to account for the Van’t Hoff factor of the solute (i). Examples are salts such as NaCl or NaOH. A nonionic-volatile solute will also cause the vapor pressure of the solvent to decrease. However, because the solute is volatile it will also have a vapor pressure. To find the overall vapor pressure of the solution the vapor pressure of the solute and the solvent must be combined. These calculations will all involve Raoult’s Law.
Raoult's Law Pa = XaPao
Pa = Vapor pressure of solution
Xa = Mol fraction of the solvent
Pao= Vapor pressure of the pure solvent
Raoult’s Law says that the vapor pressure of a solvent tends to decrease when it is part of a solution. Pa less than Pao.
Link to Video
Introduction to the Vapor Pressure of a Solution (Raoult’s Law): https://youtu.be/YZ5vTzUe0yg
Attribution
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Prof. Steven Farmer (Sonoma State University)