The table summarises some reactions of metals in the reactivity series. Hydrogen is shown for comparison.
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. Aluminium is unusual because it is a reactive metal that does not react with water. Its surface naturally forms a very thin layer of aluminium oxide that keeps water away from the metal below.
Magnesium reacts slowly when it is first added to water, but a layer of insoluble magnesium hydroxide forms. This protects the metal and stops it reacting. However, if steam is passed over hot magnesium, a vigorous reaction happens:
magnesium + steam → magnesium oxide + hydrogen
Mg(s) + H2O(g) → MgO(s) + H2(g)
In this reaction:
State the difference between the products formed when calcium reacts with cold water and when it reacts with steam.
Calcium hydroxide forms when it reacts with water, but calcium oxide forms when it reacts with steam.
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.
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. Both gold and platinum are placed below hydrogen.