# Metals and displacement reactions

### Displacement in solutions

A more can a less reactive metal from its . For example, magnesium is more reactive than copper. It displaces copper from copper sulfate :

magnesium + copper sulfate → magnesium sulfate + copper

Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)

In this :

• magnesium becomes coated with copper
• the blue colour of the solution fades as blue copper sulfate solution is replaced by colourless magnesium sulfate solution

### Determining a reactivity series

A can be produced by carrying out several displacement reactions. A piece of metal is dipped into a solution. Different combinations of metal and salt solution are tested. The table shows the results of one of these investigations.

Magnesium sulfate solutionCopper sulfate solutionZinc sulfate solutionNumber of reactions
MagnesiumNot doneBrown coatingBlack coating2
CopperNo visible reactionNot doneNo visible reaction0
ZincNo visible reactionBrown coatingNot done1

Example

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.

Question

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.

### Displacement reactions as redox reactions - Higher

A balanced equation for the reaction between magnesium and copper sulfate solution can be written in terms of the 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 . The equation can be rewritten without them:

Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)

This equation is an example of balanced . It can be split into two :

Mg(s) → Mg2+(aq) + 2e- (oxidation)

Cu2+(aq) + 2e- → Cu(s) (reduction)

Notice that:

• magnesium atoms lose - they are oxidised
• copper ions gain electrons - they are reduced

and happen at the same time, so the reactions are called .

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