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, melting into a ball, and 'fizzing' about the surface:
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.
Metals that react slowly with cold water can react quickly with steam. In these reactions a metal oxide and hydrogen are produced.
Metal + steam → metal oxide + hydrogen
For example, magnesium reacts slowly with cold water. However, if steam is passed over hot magnesium, a vigorous reaction occurs:
Magnesium + steam → magnesium oxide + hydrogen
Mg(s) + H2O(g) → MgO(s) + H2(g)
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.
Metal + acid → salt + hydrogen
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.
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.
A metal's relative tendency to form cations and its resistance to oxidation are both related to its position in the reactivity series. In general: