Question

Give three examples of reactions between metals and water, to show that different metals have different reactivities.

Answer 1

Metals react with water to form oxides or hydroxides with release of hydrogen gas.

1. Sodium and potassium react vigorously even with cold water producing hydroxides with release of enormous heat.

$$\begin{gathered} \underset{\mathrm{Sodium}}{2\mathrm{Na}}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2} \\ \underset{\mathrm{Potassium}}{2\mathrm{K}}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Potassium}\mathrm{hydroxide}}{2\mathrm{KOH}}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2} \end{gathered}$$

2. Magnesium does not react with cold water, but reacts with hot water or steam to form magnesium oxide.

$\underset{\mathrm{Magnesium}}{2\mathrm{Mg}}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Magnesium}\mathrm{oxide}}{2\mathrm{MgO}}+\underset{\mathrm{Hydrogen}}{2{\mathrm{H}}_2}$

3. Aluminium reacts with water to form a thin layer of aluminium oxide on it. This thin coating of aluminium oxide on aluminium acts as a barrier and stops further reactions.

$\underset{\mathrm{Aluminium}}{2\mathrm{Al}}+\underset{\mathrm{Water}}{3{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Aluminium}\mathrm{oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3}+\underset{\mathrm{Hydrogen}}{3\hspace{0.17em}{\mathrm{H}}_2}$

From the above examples, we can say that sodium and potassium are highly reactive, magnesium is less reactive and aluminium is least reactive. This shows that different metals have different reactivities with water.