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Summary Alevel Chemistry - Chromatography (TLC)
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- AQA
Alevel Chemistry - Chromatography (TLC)
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Chromatography (TLC)Chromatography is used to separate things in a mixture which allows the components to be
separated.
Mobile Phase - where the molecules can move. This is a liquid or gas.
Stationary Phase - where the molecules cannot move. This is a solid or liquid on solid support.
The mobile phase moves through or over the stationary phase. The distance the substance
moves depends on the solubility in the mobile phase and the retention by the stationary phase.
Components which are more soluble in the mobile phase travel further than the components
more strongly adsorbed to the stationary phase. Differences in solubility and retention separate
the different substances.
Thin Layer Chromatography (TLC)
The mobile phase is a liquid solvent such as ethanol.
The stationary phase is a thin layer of silica (silicon dioxide) or alumina (aluminium oxide) fixed
to a glass or metal plate. This is adsorbent.
1. Draw a line in pencil near the bottom of the TLC plate (the baseline) and put a very small
drop of each mixture to be separated onto the line.
2. Allow the spots on the plate to dry.
3. Place the plate in a beaker with a small volume of solvent (the mobile phase). The solvent
level must be below the baseline so the samples do not dissolve away. The top of the
beaker should be covered in a watch glass.
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