Methods Of Purification - Testing Purity Of Substances
[a pure substance has a fixed and exact melting point]
the identity of a pure solid can be deduced by its melting point.
the presence of any impurities will lower this melting point.
and if impurities are present, the mixture will melt over a range of temperatures.
[a pure substance has a fixed and exacty boiling point]
the identity of a pure liquid can be deduced by its boiling point.
the presence of any impurities will raise this boiling point,
and also cause the liquid to boil over a rance of temperatures.
[a pure substance shows only one spot on a chromatogram]
chromatography can not only seperate pigments and dyes,
it can also be used to test for the purity of a substance.
this method is especially useful with complicated chemicals like drugs or food additives which are not easily melted or distilled.
chromatography can be used to identify synthetic dyes in food and check if they are harmful, or pesticide treated vegetables which may be harmful to people.
chromatography can detect chemicals even down to very low concentrations.