Raoult's law states that the partial pressure of a volatile component of a solution is equal to the mole fraction of that component times the vapor pressure of that component. VP = vapor pressure in the equations below
Raoult's law states that the partial pressure of a volatile component of a solution is equal to the mole fraction of that component times the vapor pressure of that component.
VP = vapor pressure in the equations below
In a solution of alcohol in water,
Partial pressure of alcohol = mole fraction of alcohol x VP of alcohol Partial pressure of water = mole fraction of water x VP of water VP of the solution = VP of water + VP of alcohol
In a solution of sugar in water,
Partial pressure of water = mole fraction of water x vapor pressure of water
The vapor pressure of sugar is so low that it is not significant. (Sugar is considered nonvolatile.)
Remember that this law refers to ideal solutions where the interactions between solvent and solute molecules are identical. In most real solutions the solute molecules do interact with the solvent molecules more strongly than with each other. These interactions result in small deviations from this law.
Raoult's Law and colligative properties are reviewed several in places on the WWW.
