Which metal displaces which
From the pair of experiments on zinc and copper comes a general rule.
The principle of displacement
A metal can be displaced from a solution of its salt only by a metal more reactive than itself.
How to use it
If a reaction occurs
The metal added is more reactive than the metal in the solution.
If no reaction occurs
The metal added is less reactive than the metal in the solution.
Applied to zinc and copper
Zinc can displace copper from copper sulphate solution → zinc is the more reactive.
Copper cannot displace zinc from zinc sulphate solution → copper is the less reactive.
So of zinc (Zn) and copper (Cu) we may conclude that zinc is the more reactive metal.
All four sets of observations lead here
The reactivity of metals with oxygen, with water, with dilute acids and with the salts of other metals all differ from metal to metal. Put those observations together, arrange the metals accordingly, and you have the activity series.
In the next section we look at that series in full and at what it is good for.