magnesium + copper sulfate → magnesium sulfate + copper
Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
In this displacement reaction:
A reactivity series can be produced by carrying out several displacement reactions. A piece of metal is dipped into a salt solution. Different combinations of metal and salt solution are tested. The table shows the results of one of these investigations.
|Magnesium sulfate solution||Copper sulfate solution||Zinc sulfate solution||Number of reactions|
|Magnesium||Not done||Brown coating||Black coating||2|
|Copper||No visible reaction||Not done||No visible reaction||0|
|Zinc||No visible reaction||Brown coating||Not done||1|
Use the results in the table to deduce an order of reactivity, starting with the most reactive metal.
The order of reactivity is: magnesium > zinc > copper. This is because magnesium could displace copper and zinc, zinc could only displace copper, but copper could not displace magnesium or zinc.
Explain why three combinations of metal and salt solution were not done in the investigation.
A metal cannot displace itself from a solution of one of its salts. There would be no reaction, so these combinations were not done.
A balanced equation for the reaction between magnesium and copper sulfate solution can be written in terms of the ions involved:
Mg(s) + Cu2+(aq) + SO42-(aq) → Mg2+(aq) + SO42-(aq) + Cu(s)
Notice that sulfate ions, SO42-, appear on both sides of the equation. They do not take part in the reaction and are called spectator ions. The equation can be rewritten without them:
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)
Mg(s) → Mg2+(aq) + 2e- (oxidation)
Cu2+(aq) + 2e- → Cu(s) (reduction)