An ideal solution is any solution which obeys Raoult's law. Raoult's law gives the relationship between a solution's vapor pressure and a solvent's vapor pressure when the solute has no measurable vapor pressure (is nonvolatile). The law is stated as follows: "The partial pressure of a solvent over a solution, P1, is given by the vapor pressure of the pure solvent, P°1, times the mole fraction of the solvent in the solution, X1," or P1 = X1·P°1