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Chemical Analysis
Chemistry 2A…read more

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Paper chromatography can be used to identify the different substances in a
mixture (usually used to identify the different coloures in a dye). We can do so
using the following method.
¬First make a straight pencil* baseline on some tracing paper. The number of new dots that appear on the
paper doesn't tell you exactly how many
¬You'd need to fill a beaker with solvent (e.g. water, salt water, dyes are in the mixture. It tells you that
or ethanol). there are at least that many dyes in the
¬Place a small spot of the mixture on the baseline. mixture.
¬Then put the paper into the beaker, making sure that the
baseline is above the level of the solvent*.
¬The solvent will begin to seep up the paper, carrying the dyes
with it. The different dyes in the samples will form separate
spots on the paper.
*We use pencil for the baseline because it doesn't interfere with the process. If we used
pen the dyes in the ink would be carried up by the solvent and ruin the experiment
*The baseline is kept above the level of the solvent because if it wasn't, the substances
would be washed away by the solvent rather than being carried by the solvent.
*A lid could be placed on the beaker to prevent evaporation…read more

Slide 3

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Gas Chromatography
Gas chromatography is an instrumental method of identifying substances. It allows the
separation of a mixture of compounds.
¬Gas is used to carry the mixture through a column that's packed with solid material
¬The different substances inside of the mixture have different masses, which means that they travel though the column
at different times. This is what separates the different substances in the mixture.
¬The time that it takes for the different substances to pass through the column is called the retention time. The
retention times of the substances are recorded by the detector.
¬The detector passes on the retention times to a recorder, which draws up a gas chromatograph. The graph shows the
number of compounds in the sample.
The chromatography column can be attached to a mass spectrometer (GC-MS), which identifies the substances leaving the column
very accurately. It does show by drawing a graph showing the relative molecular mass of the substances.…read more

Slide 4

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Instrumental methods
In general, instrumental methods of analysing unknown substances are better than others
¬They're very sensitive, so you can use small samples of substances
¬They're fast
¬They're accurate…read more


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