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Knowledge database: Basics: Separation methods

A mixture of different substances can be divided by making use of their different chemical or physical properties. Here we will provide some of the basic and most common methods which chemists use:

Filtration is a process of separation of suspended matter from liquids or solutions. The simplest form of filtering is through a funnel into which a filter paper has been inserted. There are also more complex ways of filtration, mostly based on creating a vacuum.

Dissolution is a process by which soluble substances are separated from the insoluble. Insoluble substances can then be extracted from the liquid by using filtration, while the dissolved matter may be obtained by evaporation, distillation or other methods.

Sedimentation and floatation are procedures that are useful in cases when one has a substance which is substantially heavier or lighter than the substance in which it is suspended. Because of this, the substance either floats on the surface of the liquid in which it is suspended, or it sinks if it is heavier. When that occurs, one can simply separate the layers by using pipettes or pouring each layer in its separate container. This procedure is also known as decantation.

Centrifugation is a procedure that is based on sedimentation/floatation, but the process is significantly accelerated by using centrifugal force that causes the heavier particles to quickly settle to the bottom. There are hand centrifuges that can achieve forces about 100 times greater than gravity, but there are also centrifuges using electric motors that can achieve extremely high forces, up to several hundred thousand times higher than gravity.

Magnetic separation is useful when one wants to separate magnetic substances from non-magnetic matter.

Distillation is a process which involves separating lighter and more volatile liquids from heavier and less volatile substances. The production of spirits is one of the examples where distillation is used. Mixtures containing fermented fruits, among other substances, contain alcohol mixed with water. When the distillation process starts, the substance that first leaves the solution is alcohol as a lighter and more volatile substance. Water also evaporates, but more slowly than alcohol. Because of that, at the start, the amount of water that evaporates, isn't high, but it increases with time. The alcohol and water steam passes through a pipe which is immersed in cold water. Because of that, the steam condenses, and the final result is a spirit coming out of the pipe. This process, which turns steam (gases) into liquid by passing them through a cooler medium, is called condensation.

Sublimation is a process of separating substances that sublime, from the ones that don't (direct transition from solid to gas, without the liquid state in between (the standard example for this is elemental iodine)).

There are also many other separation processes, but these are the most common which chemists usually face.

chemistry tutorials - separation methods

Some of the most common separation methods used by chemists: A) filtration, B) distillation.


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