The Separation of Mixtures
A ‘mixture’ can be defined as a material containing two or more distinct substances that are not chemically combined. The aim of separating a mixture is to produce two or more individual compounds that are physically distinct from each other. To separate a mixture, the components need to be identified and characterised. These include the solubility of the substance/s, their melting and boiling points and their density.
Once these properties have been identified, the most appropriate separation techniques can be identified. A common example of a separation method is distillation. This process involves heating a mixture in order to evaporate the more volatile components, followed by a cooling process to condense the resultant vapours.
When dealing with a solution of two or more liquids that are immiscible, decanting is a suitable method of separation. This involves very carefully pouring off the top layer of liquid without disturbing the bottom layer. The amount of each liquid that is decanted depends on the specific gravity of the liquid, which determines the order in which it is decanted.
Filtration is another useful method of separation. This involves a filtration medium being used to filter out solid substances particles from the mixture. The particles are then collected on top of the medium, while the filtered liquid passes through. The particles can then be collected, washed and dried (if necessary) to obtain the desired result.
Another common separation method is crystallisation. This requires a solute to be dissolved in a solvent and heated until it reaches the desired concentration. The solution is then cooled and allowed to crystallise. This results in the precipitation of solid crystals, which can then be collected and separated from the solution.
Centrifugation is a method of separating a mixture using centrifugal force. This can be used to separate components of different densities, as the lighter particles will be thrown out to the edge of the rotor while the heavier particles will remain at the centre. This method is often used to separate components of a biological sample such as cells, soluble proteins and particulate matter.
Finally, chromatography is a technique that involves separating components of a mixture based on the different rates at which they move when a mobile phase is applied. This can be used to separate molecules from other molecules of different molecular weight, as well as separating ionic molecules from non-ionic molecules.
There are a wide range of methods that can be used to separate mixtures, depending on the properties of the components. The best choice of method will depend on the type of mixture, the properties of its components and the desired result. An experienced researcher or practitioner should be consulted in order to ensure that the most appropriate method is used.
