The reactivity series of metals

When metals react with other substances, the metal atoms lose electrons to form positive ions.

The reactivity series of metals is a chart showing metals in order of decreasing reactivity. In general, the more reactive a metal is:

  • the more vigorous its reactions are
  • the more easily it loses electrons in reactions to form positive ions

The table summarises some reactions of metals in the reactivity series. Hydrogen and carbon are shown for comparison.

List of metals with the reaction with cold water, reaction with dilute acids and reactivity.

Reactions of metals with water

When a metal reacts with water, a metal hydroxide and hydrogen are formed. For example, sodium reacts rapidly with cold water:

Sodium + water → sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

In general, the more reactive the metal, the more rapid the reaction is.

Question

Describe and explain the observations when a small piece of lithium is placed on the surface of a big container of water. A few drops of universal indicator have been added to the water.

There is fizzing as the lithium reacts with the water to produce hydrogen gas. The colour of the universal indicator changes from green to purple as an alkaline solution of lithium hydroxide is produced.

Reactions of metals with dilute acids

When a metal reacts with a dilute acid, a salt and hydrogen are formed. For example, magnesium reacts rapidly with dilute hydrochloric acid:

Magnesium + hydrochloric acid → magnesium chloride + hydrogen

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

The more reactive the metal, the more rapid the reaction is. A metal below hydrogen in the reactivity series will not react with dilute acids.

Question

Platinum is placed below gold in the reactivity series. Predict its reaction with dilute acids and explain your answer.

Platinum will not react with dilute acids. Metals below hydrogen in the reactivity series do not react with dilute acids, and both gold and platinum are placed below hydrogen.

curriculum-key-fact
Hydrogen is always made when a metal reacts with water or a dilute acid.