Explaining reactivity
Extended tier only
- 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
Displacement reactions between metals and aqueous solutions of metal salts
- Any metal will displace another metal that is below it in the reactivity series from a solution of one of its salts
- This is because more reactive metals lose electrons and form ions more readily than less reactive metals, making them better reducing agents
- The less reactive metal is a better electron acceptor than the more reactive metal, thus the less reactive metal is reduced
- OILRIG: reduction is gain of electrons
Magnesium + copper sulfate
- Magnesium is a reactive metal and can displace copper from a copper sulfate solution
- Magnesium loses its electrons more easily and the ion of the less reactive metal, copper, will gain these electrons to form elemental copper
- This is easily seen as the more reactive metal slowly disappears from the solution, displacing the less reactive metal
magnesium + copper sulfate → magnesium sulfate + copper
Mg (s) + CuSO4 (aq) → MgSO4 (aq) + Cu (s)
- 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
The reaction between magnesium and copper sulfate
Diagram showing the colour change when magnesium displaces copper from copper sulfate
- By combining different metals and metal salts solutions it is possible to come up with a relative reactivity order
Metal Solutions Displacement Table
| Mixture | Products | Equation for Reaction |
| Magnesium and iron(II) sulfate | Magnesium sulfate and iron | Mg + FeSO4 → MgSO4 + Fe |
| Zinc and iron chloride | Zinc chloride and iron | Zn + FeCl2 → ZnCl2 + Fe |
| Iron and silver nitrate | Iron(II) nitrate and silver | Fe + AgNO3 → Fe(NO3)2 + 2Ag |
| Copper and iron(II) chloride | No reaction | ------ |
| Silver and copper(II) sulfate | No reaction | ------ |
| Zinc and magnesium chloride | No reaction | ------ |
- From this table we can deduce the order of reactivity:
- Magnesium and zinc are both more reactive than iron but magnesium is more reactive than zinc
- Copper and silver are both less reactive than iron but silver is less reactive than copper
- The order of reactivity of the metals tested can be therefore be deduced as:
- Mg > Zn > Fe > Cu > Ag
