Paper chromatography
Paper Chromatography is used to separate different substances dissolved in a liquid. is used to separate mixtures of Able to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.
Image caption, Paper chromatography
1. Ink or plant dye is dotted along the pencil line.
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Phases
Chromatography relies on two different âphasesâ:
- the Phase in chromatography that does not move, for instance, the paper in chromatography., which in paper chromatography is very uniform, absorbent paper
- the Phase in chromatography that moves, usually a solvent or mixture of solvents. is the The liquid in which the solute dissolves to form a solution. that moves through the paper, carrying different substances with it
The different A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution. substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.
Interpreting a chromatogram
Separation by chromatography produces a The results of separating mixtures by chromatography.. A paper chromatogram can be used to distinguish between pure and impure substances:
- a pure substance produces one spot on the chromatogram
- an impure substance, or mixture, produces two or more spots
A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:
- they produce the same number of spots, and these match in colour
- the spots travel the same distance up the paper