Separation Techniques

About this topic

Mixtures can be separated by physical methods that exploit differences in properties. Filtration removes insoluble solids from liquids, evaporation recovers dissolved solids, distillation separates liquids by boiling point, and chromatography separates substances by how they travel through a medium. Others include decanting, magnetism and using a separating funnel.

Each method works because the components have different properties. A filter paper has pores that let water through but trap sand. In distillation, the liquid with the lower boiling point vaporises first, travels through a condenser, and is collected as a purer liquid. In chromatography, ink spots rise up paper with a solvent, and each dye moves a different distance depending on how soluble it is and how strongly it sticks to the paper.

To separate a mixture of sand, salt and iron filings, you could first use a magnet to remove the iron, then add water to dissolve the salt, filter off the sand, and finally evaporate the water to get the salt crystals back. Real uses include getting drinking water from seawater, refining crude oil, purifying medicines, and testing athletes for banned drugs.

Remember to choose the method from the property difference, and that these are physical changes, so the components are not altered. A misconception is that filtration separates salt from water; dissolved particles are too small and pass straight through.