Reactivity of Metals (Edexcel GCSE Chemistry: Combined Science)

• The chemistry of the metals is seen by comparing their characteristic reactions
• Based on these reactions a reactivity series of metals can be produced
• The series can be used to place a group of metals in order of reactivity based on the observations of their reactions with water, acids and salts

The Relative Reactivity of Metals with Water and Acids

Reaction with water

• In general, when a metal reacts with water it produces a metal hydroxide and hydrogen gas
• The reactions of potassium and sodium are covered in more detail in another section, but the reaction with calcium and water is given here for reference:

Ca (s) + 2H₂O (l) ⟶ Ca(OH)₂ (aq)  + H₂ (g)

calcium + water ⟶ calcium hydroxide + hydrogen

• The reactions with magnesium, iron and zinc and cold water are very slow

Reaction with dilute acids

• Only metals above hydrogen in the reactivity series will react with dilute acids
• The more reactive the metal then the more vigorous the reaction will be
• Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids
• When acids react with metals they form a salt and hydrogen gas:
• The general equation is:

metal + acid ⟶ salt + hydrogen

• Some examples of metal-acid reactions and their equations are given below:

Acid-Metal Reactions Table 

Reaction with 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 color 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 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

• From this table we can see that the relative reactivity of the pairs of metals is
  • Mg > Fe
  • Pb > Ag
  • Fe > Cu

Explaining Reactivity

• In all these reactions the more reactive metals lose electrons to become cations
• The more reactive the metal the more easily it becomes a cation:

M ⟶ Mⁿ⁺  +  ne^-

• The loss of electrons is oxidation
• The higher up the metal is in the reactivity series the more easily it will undergo oxidation
• Unreactive metals are therefore more resistant to oxidation