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Separation Methods - Arwa Sadeq - 10S - Chemistry - Ms Dalia - 23/09/2021 …
Separation Methods - Arwa Sadeq - 10S - Chemistry - Ms Dalia - 23/09/2021
Separating mixtures
The individual substances in a mixture can be separated using different methods, depending on the type of mixture. These methods include filtration, evaporation, distillation and chromatography.
Filtration
Separating solids from liquids
If a substance does not dissolve in a solvent, we say that it is insoluble. For example, sand does not dissolve in water – it is insoluble.
Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered:
the sand stays behind in the filter paper (it becomes the residue)
the water passes through the filter paper (it becomes the filtrate)
A beaker containing a mixture of insoluble solid and liquid. There is filter paper in a filter funnel above another beaker.
Evaporation
Separating solids from liquids
Evaporation is used to separate a soluble solid from a liquid. For example, copper sulfate is soluble in water – its crystals dissolve in water to form copper sulfate solution. During evaporation, the water evaporates away leaving solid copper sulfate crystals behind.
A solution is placed in an evaporating basin and heated with a Bunsen burner.
simple distillation
Separating the solvent from a solution
Simple distillation is a method for separating the solvent from a solution. For example, water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
Every pure substance has its own particular melting point and boiling point. One way to check the purity of the separated liquid is to measure its boiling point. For example, pure water boils at 100°C. If it contains any dissolved solids, its boiling point will be higher than this.
fractional distillation
Separating a liquid from a mixture
Fractional distillation is a method for separating a liquid from a mixture of two or more liquids. For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.
One way to check the purity of the separated liquids is to measure their boiling points. For example, pure ethanol boils at 78°C and pure water boils at 100°C.
chromatography
Paper chromatography is a method for separating dissolved substances from one another. It is often used when the dissolved substances are coloured, such as inks, food colourings and plant dyes. It works because some of the coloured substances dissolve in the solvent used better than others, so they travel further up the paper.
A pure substance will only produce one spot on the chromatogram during paper chromatography. Two substances will be the same if they produce the same colour of spot, and their spots travel the same distance up the paper. In the example below, red, blue and yellow are three pure substances. The sample on the left is a mixture of all three.
