Reactivity of metals

Metals can be put in order of how readily they react: the reactivity series. Potassium, sodium and lithium react vigorously with water; gold hardly reacts at all. The series predicts which metal displaces another from its compounds, and it decides how each metal is got out of its ore: by heating with carbon, by electrolysis, or not at all for gold.

Key facts

  • The series: potassium, sodium, lithium, calcium, magnesium, aluminium, (carbon), zinc, iron, tin, lead, (hydrogen), copper, silver, gold. Carbon and hydrogen are there to compare.
  • The more reactive a metal, the more easily it loses electrons to form positive ions.
  • Reactive metals + water → metal hydroxide + hydrogen. Metals above hydrogen + dilute acid → salt + hydrogen; copper, silver and gold do not react with dilute acids.
  • Displacement: a more reactive metal pushes a less reactive metal out of a solution of its compound. zinc + copper sulfate → zinc sulfate + copper.
  • An ore is a rock containing enough metal compound to be worth extracting. Gold is so unreactive that it is found as the metal.
  • Metals below carbon are extracted by heating their oxides with carbon: the oxide is reduced (loses oxygen). Metals above carbon need electrolysis.
  • In displacement, the more reactive metal is oxidised (loses electrons) and the ions of the less reactive metal are reduced (gain electrons).

Worked examples

Example 1

Iron nails are put into copper sulfate solution. What do you see, and what is the word equation?

  1. Iron is above copper in the reactivity series, so iron displaces copper.
  2. iron + copper sulfate → iron sulfate + copper
  3. Brown copper coats the nails, and the blue copper sulfate fades as it is used up (iron sulfate solution is pale green).

Answer: a brown coating of copper forms and the blue colour fades; iron + copper sulfate → iron sulfate + copper

Example 2

How would you extract iron from iron oxide, and aluminium from aluminium oxide?

  1. Iron is below carbon, so carbon can take the oxygen from iron oxide: iron oxide + carbon → iron + carbon dioxide. The iron oxide is reduced.
  2. Aluminium is above carbon, so carbon cannot reduce aluminium oxide.
  3. Aluminium is extracted by electrolysis of the molten oxide, which needs a lot of electricity.

Answer: iron: heat with carbon; aluminium: electrolysis of the molten oxide

Example 3

Metal X displaces copper from copper sulfate but not zinc from zinc sulfate. Metal Y does not displace copper. Put X, Y, zinc and copper in order of reactivity.

  1. X displaces copper, so X is more reactive than copper.
  2. X does not displace zinc, so zinc is more reactive than X.
  3. Y does not displace copper, so copper is more reactive than Y. Order: zinc > X > copper > Y.

Answer: zinc, X, copper, Y (most reactive first)