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Hannah's SEPARATION OF SOLID-LIQUID MIXTURES, 2.The chromatographic…
Hannah's SEPARATION OF SOLID-LIQUID MIXTURES
Chromatography
It is useful to separate and identify small amounts of substances that are dissolved in a solvent,
such as dyes in coloured ink.
The features of chromatography:
a lid
solvent front
components in the sample
starting line
solvent
Chromatography can be used to separate different components in a mixture based on the following principles:
Different components in a mixture have different solubility in a solvent.
The different solubility in a solvent causes them to move at different speeds on the chromatography paper.
The process of chromatography:
1.A small amount of concentrated sample is placed on the starting line of a chromatographic paper.
A few precautions when carrying out the process of paper chromatograhy:
Draw the starting line with a pencil and not a pen The starting line is the location where a sample is placed.
A pencil is an element
so it is not made of dyes and will not be separated by the solvent to interfere the results.
ink is made up of dyes which can dissolve in the solvent and interfere the results.
Use fine capillary tubes to place a small and concentrated sample on the paper.
This prevents the overlapping of components so that a clear and distinct lines or spots can be obtained
The solvent should be below the starting line.
This prevents the sample from dissolving into the solvent so that it can travel up the paper
The solvent front should be as high as possible.
It ensures that the components in a sample are fully separated
The jar should be covered with a lid when a volatile solvent such as alcohols is used
it prevents the solvent from evaporating too fast
it also ensures that the jar is saturated with the solvent vapour
This facilitates the movement of the solvent as it will not evaporate from the paper too quickly
the result of the separated components on the chromatography paper is called chromatogram.
2.The chromatographic paper is placed inside a beaker containing a solvent.
The solvent is below the starting line.
3.As the solvent moves up the paper, it separates the sample into its respective components.
4.The chromatographic paper is removed before the solvent reaches the edge of the other end of the paper.