A more reactive metal will displace a less reactive metal from a solution of one of its salts. For example:
magnesium + copper(II) sulfate → copper + magnesium sulfate
Mg(s) + CuSO4(aq) → Cu(s) + MgSO4(aq)
In this reaction, the blue colour of the copper(II) sulfate fades as it is used up (magnesium sulfate solution is colourless). We would also see copper metal (red/brown solid) forming.
Reactions between metals and solutions of metal salts allow us to put a selection of metals into a reactivity series. Using metals J, K and L:
|Metal J||Metal K||Metal L|
|J sulfate||X||No reaction observed||No reaction observed|
|K sulfate||Displaces K||X||Displaces K|
|L sulfate||Displaces L||No reaction observed||X|
Note that the displacement is observed by a change in colour of the metal and/or a change in colour of the solution.
Therefore, the order is: