If this vapor escapes, more pentane leaves the system than octane, and the percent by mass of octane in the system increases. This increases the boiling point of the mixture, as well as gradually increasing the amount of octane that collects in the vapor that escapes from the liquid. This phase diagram therefore provides the basis for separating a mixture by distillation. We start by heating the mixture and collecting the first few portions, or fractions, that distill over. These fractions will be rich in the component that has the lower boiling point.
Distillation works best for purifying compounds that are liquids at room temperature.
Solids are more likely to be purified by recrystallization , which takes advantage of differences in the solubility of various components of a mixture in different solvents. We start by dissolving as much of the solid as possible in a hot sample of the solvent. We then cool the solution until some of the solid crystallizes back out of solution. Each time the sample is dissolved and recrystallized, it is purer than before. This was the technique used by Marie and Pierre Curie to isolate the first minuscule sample of radium from several tons of the mineral pitchblende.