Chromatography

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What is chromatography used for?
To identify different substances in a mixture.
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What is the chromatography method?
First, put spots of each mixture on a pencil baseline on filter paper.
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What is the second step?
Put the paper into a beaker containing a solvent. The baseline must be kept above the level of solvent.
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Why must the baseline be kept above the liquid?
The paper will absorb the solvent which will travel up the paper, bringing out the different substances. If it was in the water, the substances would just be washed away.
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What happens once the paper is in the beaker?
The solvent seeps up the paper and takes the samples with it. The different chemicals in the sample form separate spots on the paper.
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What are these results known as?
The result of a chromatography analysis is called a chromatogram.
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How can you analyse a chromatogram?
Chromatography is often used to recognise the different colouring agents in food. E.g. you put a spot of pink food colouring on the pencil baseline and as the solvent seeps up, more spots of colours other than pink begin to appear above the original.
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Continued
There may be one dot or even three of four of different colours. This would show the pigments within the pink food colouring.
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What is an Rf value?
An Rf value is the ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
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What formula can be used to find an Rf value?
Rf = the distance travelled by substance DIVIDED BY the distance travelled by the solvent.
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Other cards in this set

Card 2

Front

What is the chromatography method?

Back

First, put spots of each mixture on a pencil baseline on filter paper.

Card 3

Front

What is the second step?

Back

Preview of the front of card 3

Card 4

Front

Why must the baseline be kept above the liquid?

Back

Preview of the front of card 4

Card 5

Front

What happens once the paper is in the beaker?

Back

Preview of the front of card 5
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