Separation Techniques

A little bit of revision first of all. A mixture contains two or more substances which have not reacted chemically with each other. A mixture is made of little bits of each substance mixed together.

A mixture can be separated by physical methods, a compound can not.

For example:
A mixture of iron filings and sulphur can be separated by using a magnet to attract the iron.
Iron is a magnetic material but sulphur is not.

If a mixture of iron filings and sulphur is heated the iron reacts with the sulphur and the compound iron sulphide [FeS] is formed which is not a magnetic material and cannot be separated by using a magnet.

Separation Techniques – Physical Methods.

Filtration

Crystallisation

Distillation

Chromatography

We’ve already covered paper chromatography and Rf values. You should be able to work these outThese compounds are coloured. What if they're colourless? We calculate a number between 0 and 1 – the smaller distance travelled by the pigment divided by the larger distance travelled by the solvent. This is the Rf value for this pigment. The yellow pigment has a value of 14.5/18.5 = 0.78.

Here’s a thought. Sometimes the ‘pigments’ are colourless.  What can we do with these?  Here’s the answer.

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