In other sections of this book, you have looked at ions, what they are, how they are made and we have referred to an expression "oxidation state" which is used to indicate how many electrons particular element has lost or gained to become positively or negatively charged respectively.


If a sample of a substance was placed in front of you, for example a small amount of a white crystalline solid, would you know just by looking at it what it was? Unless you saw the container it came from (and then there are no guarantees), I would say that the answer is almost certainly no. 



Fortunately there are tests that we can carry out which allow us to identify the components of substances present in a chemical compound. Tests for the presence of positive or negative ions, and certain specified types of ion will be outlined in this section.