# Raoult's Law - How To Calculate The Vapor Pressure of a Solution | Summary and Q&A

364.8K views
January 23, 2021
by
The Organic Chemistry Tutor
Raoult's Law - How To Calculate The Vapor Pressure of a Solution

## TL;DR

Raoult's Law states that adding a non-volatile solute to a solvent decreases the vapor pressure of the solution. The video explains how to calculate vapor pressure using Raoult's Law.

## Install to Summarize YouTube Videos and Get Transcripts

### Q: What is Raoult's Law?

Raoult's Law is a formula that describes the relationship between the vapor pressure of a solution and the mole fraction of the solvent. It states that the vapor pressure of the solution is equal to the mole fraction of the solvent multiplied by the vapor pressure of the solvent.

### Q: How does adding a non-volatile solute affect the vapor pressure of a solution?

Adding a non-volatile solute to a solvent decreases the vapor pressure of the solution. This is because the presence of the solute disrupts the solute-solvent interactions, making it harder for solvent molecules to escape into the gas phase.

### Q: How do you calculate the mole fraction of the solvent?

To calculate the mole fraction of the solvent, divide the moles of the solvent by the total moles in the solution, which is the moles of the solvent plus the moles of the solute.

### Q: How can Raoult's Law be used to calculate the vapor pressure of a solution?

Once the mole fraction of the solvent is determined, it can be multiplied by the vapor pressure of the pure solvent to calculate the vapor pressure of the solution.

## Summary & Key Takeaways

• Raoult's Law states that the vapor pressure of a solution is the product of the mole fraction of the solvent and the vapor pressure of the solvent.

• By calculating the moles of water and the moles of solute in a solution, the mole fraction of the solvent can be determined.

• Using Raoult's Law, the vapor pressure of the solution can then be calculated.