A mixture is separated by choosing a physical technique that exploits a difference in particle properties, such as particle size, boiling point, solubility, or attraction to another substance. The correct method depends on the mixture and the component that must be collected.
How Each Separation Method Works
Separation is a physical process: no new substances are formed, and the chemical identities of the components remain unchanged. This links to the IB particulate model because different particles retain different physical properties within a mixture.
| Method | Property used and suitable mixture | Mechanism |
|---|---|---|
| Filtration | Particle size; an insoluble solid mixed with a liquid | Liquid and dissolved particles pass through the filter paper as the filtrate. The insoluble solid remains as the residue. |
| Distillation | Difference in boiling points; a solution or mixture of liquids | The more volatile component vaporizes first. Its vapor is cooled in a condenser and collected as the distillate. Simple distillation can recover a solvent from a solution, while fractional distillation separates miscible liquids with different boiling points. |
| Chromatography | Different relative attractions to stationary and mobile phases; soluble substances | Components travel at different rates because they have different attractions to the stationary phase and different solubilities in the mobile phase. Stronger attraction to the mobile phase produces greater movement. |
| Recrystallization | Difference in solubility with temperature; an impure soluble solid | The solid is dissolved in a minimum volume of hot solvent. On cooling, the desired substance crystallizes while soluble impurities remain in solution. The crystals are then filtered and dried. |