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.
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.
We’ve already covered paper chromatography and Rf values. You should be able to work these out 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.