Chemistry Mock Revision

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Paper Chromatography

Paper chromatography is a separation technique that is used to separate and identify the components of a mixture.

Paper chromatography is used to identify the colouring agents (chemicals) for example in food or ink. The mixture is put onto filter paper that is placed in a suitable solvent

As the solvent rises up the filter paper the individual components (dyes) within the green ink spots are separated. Different dyes travel different distances up the paper. The solvent travels furthest up the filter paper leaving a line called the solvent front.

Paper chromatography is used by the food industry and forensic science.

In gas chromatography a small sample of mixture of compounds is vaporised (turned into gas). A carrier gas takes the sample through the column. The carrier gas (often nitrogen) must be inert and not react with the sample.

The column is packed with a solid material which slows the sample down. Different compounds travel through the column at different times. The amount of time a particular compound takes to pass through the instrument is called its retention time. The retention time can help identify the compound.

A recorder draws a graph called a gas chromatograph which shows a peak for each compound. The number of peaks show the number of compounds present in the sample and the position of the peaks show the retention time.

A more accurate way of identifying the different compounds which leave the column can be made by using a mass spectrometer.

cALCULATING RELATIVE FORMula mass

Paper CHROMATOGRAPHY

Gas chromatography

PERCENTAGE by mass in an element