Metal Reactivity
The Reactivity Series
- Based on how they react with other substances, a reactivity series can be produced in which the metals are placed in order of their reactivity
- Metal atoms form positive ions by loss of electrons when they react with other substances
- The tendency of a metal to lose electrons is a measure of how reactive the metal is
- A metal that is high up on the series loses electrons easily and is thus more reactive than one which is lower down on the series
- Note that although carbon and hydrogen are non-metals, they are included in the series as they are useful in extracting metals from their oxides by reduction processes
The Reactivity Series
The reactivity of metals decreases going down the reactivity series
- A displacement reaction occurs when a more reactive metal will displace a less reactive metal from its compounds
- This can occur by:
-
- Reacting a metal with a metal oxide (by heating)
- Reacting a metal with an aqueous solution of a metal compound
- It is possible to reduce copper(II) oxide by heating it with zinc
- The reducing agent in the reaction is zinc
Zn + CuO → ZnO + Cu
zinc + copper oxide → zinc oxide + copper
Metal Oxide Displacement Table
| Mixture | Products | Equation for Reaction |
| Iron(III) oxide and aluminium - thermite reaction | Iron and aluminium oxide | Fe2O3 + 2Al → 2Fe + Al2O3 |
| Sodium oxide and magnesium | No reaction as sodium is above magnesium | ----- |
| Silver oxide and copper | Silver and copper(II) oxide | Ag2O + Cu → 2Ag + CuO |
| Zinc oxide and calcium | Zinc and calcium oxide | ZnO + Ca → Zn + CaO |
| Lead(II) oxide and silver | No reaction as lead is more reactive than silver | ------ |
| Iron nail and copper(II) chloride | Copper and iron(II) chloride | Fe + CuCl2 → FeCl2 + Cu |
Thermite
- The thermite reaction is a highly exothermic reaction that occurs when iron(III) oxide is reacted with aluminium metal
- As aluminium is more reactive than iron, the iron in iron(III) oxide is displaced
iron(III) oxide + aluminium → iron + aluminium oxide
Fe2O3 + 2Al → 2Fe + Al2O3
- The reaction releases so much heat that the iron formed is molten so this process is used in welding and incendiary devices
Displacement reactions between metals & aqueous solutions of metal salts
- The reactivity between two metals can be compared using displacement reactions in salt solutions of one of the metals
- This is easily seen as the more reactive metal slowly disappears from the solution, displacing the less reactive metal
- For example, magnesium is a reactive metal and can displace copper from a copper sulfate solution:
Mg + CuSO4 → MgSO4 + Cu
- The blue colour of the CuSO4 solution fades as colourless magnesium sulfate solution is formed.
- Copper coats the surface of the magnesium and also forms solid metal which falls to the bottom of the beaker
Diagram showing a displacement reaction
The colour of the solution changes when magnesium displaces copper from copper sulfate
Other displacement reactions
Metal Solutions Displacement Table
| Mixture | Products | Equation for Reaction |
| Magnesium and iron(II) sulfate | Magnesium sulfate and iron | Mg + FeSO4 → MgSO4 + Fe |
| Zinc and sodium chloride | No reaction as sodium is above zinc | ------ |
| Lead and silver nitrate | Lead(II) nitrate and silver | Pb + AgNO3 → Pb(NO3)2 + Ag |
| Copper and calcium chloride | No reaction as calcium is above copper | ------- |
| Iron and copper(II) sulfate | Iron(II) sulfate and copper | Fe + CuSO4 → FeSO4 + Cu |
Examiner Tip
You should have an awareness of the approximate position of common metals (and carbon and hydrogen) in the reactivity series but you do not need to be able to recall the reactivity series
