Oil and water do not mix together, because they cannot dissolve in each other, as you can see in the picture. They are immiscible liquids.
Even if we shake and mix them, they will soon separate, when the mixture is left to stand still for a while. It is easy to separate them, using a separating funnel. The tap at the bottom is opened and water which sets below oil would run out.
Miscible liquids, on the other hand, are much harder to separate, because they dissolve in each other. An example is crude oil, which is separated into the different products by fractional distillation (this is covered in another worksheet). Fractional distillation is also used to obtain nitrogen and oxygen from air. The diagram below illustrates how it happens. Air is filtered to remove dust and then cooled to -200 °C. As the air is liquefied, water vapour and carbon dioxide are removed and oxygen and nitrogen are collected from separate exits at the temperatures shown in the diagram.
Chromatography is another technique used to separate mixtures of colour compounds like inks and dyes. A spot of the mixture is placed on a special piece of paper (see diagram below) and it is allowed to soak up a solvent. As it soaks it the solvent separates the different components because they travel different distances at the same time.
Components have set Rf values when chromatography is conducted in the exact same way, so the substances can be identified by scientists. It is calculated with this formula: