Raoult's Law Calculator
Calculate vapor pressure of ideal solutions using Raoult's law with moles or mole fractions
Calculate Vapor Pressure with Raoult's Law
Vapor pressure of the pure solvent at given temperature
Amount of dissolved substance (mol)
Amount of solvent substance (mol)
Raoult's Law Formula
Basic equation: psolution = xsolvent × p°solvent
Mole fraction: x = nsolvent ÷ (nsolvent + nsolute)
Vapor pressure lowering: Δp = p° - p = xsolute × p°
Relative lowering: Δp/p° = xsolute
Example Calculation
Sugar Water Solution Example
Problem: Calculate vapor pressure of sugar water solution
Given: Pure water vapor pressure = 23.8 mmHg at 25°C
Solution composition: 0.5 mol sugar + 10 mol water
Total moles: 0.5 + 10 = 10.5 mol
Step-by-Step Solution
1. Calculate mole fraction of water: xwater = 10 ÷ 10.5 = 0.952
2. Apply Raoult's law: psolution = 0.952 × 23.8 mmHg
3. Calculate result: psolution = 22.66 mmHg
4. Pressure lowering: Δp = 23.8 - 22.66 = 1.14 mmHg
Result: Solution vapor pressure = 22.66 mmHg
Common Solvents (25°C)
Water (H₂O)
23.8 mmHg at 25°C
Ethanol (C₂H₅OH)
59.3 mmHg at 25°C
Methanol (CH₃OH)
127.2 mmHg at 25°C
Acetone (C₃H₆O)
230 mmHg at 25°C
Benzene (C₆H₆)
95.1 mmHg at 25°C
Toluene (C₇H₈)
28.4 mmHg at 25°C
Diethyl Ether
537 mmHg at 25°C
Chloroform (CHCl₃)
197 mmHg at 25°C
Raoult's Law Principles
Applies to ideal solutions only
Solute must be non-volatile
Vapor pressure is proportional to mole fraction
Solution pressure is always lower than pure solvent
Temperature affects vapor pressure significantly
Understanding Raoult's Law
What is Raoult's Law?
Raoult's law states that the vapor pressure of an ideal solution is proportional to the mole fraction of the solvent in the solution. It describes how the vapor pressure of a solution changes when a non-volatile solute is added to a volatile solvent.
Key Applications
- •Calculating molecular mass of unknown solutes
- •Determining solution concentrations
- •Understanding colligative properties
- •Analyzing vapor-liquid equilibrium
Mathematical Formulations
p = x × p°
x = nsolvent / (nsolvent + nsolute)
Δp = p° - p = xsolute × p°
Limitations
- Ideal solutions only: No intermolecular interactions
- Non-volatile solutes: Solute must not evaporate
- Dilute solutions: Most accurate at low concentrations
- Similar molecules: Works best for chemically similar components
Remember: Real solutions often deviate from Raoult's law due to molecular interactions.