Magnesium: reactions of elements

Reaction of magnesium with air

Magnesium is a silvery white metal. The surface of magnesium metal is covered with a thin layer of oxide that helps protect the metal from attack by air. Once ignited, magnesium metal burns in air with a characteristic blinding bright white flame to give a mixture of white magnesium oxide, MgO, and magnesium nitride, Mg3N2. Magnesium oxide is more normally made by heating magnesium carbonate. Calcium, immediately below magnesium in the periodic table is more reactive with air than magnesium.

2Mg(s) + O2(g) → 2MgO(s)

3Mg(s) + N2(g) → Mg3N2(s)

Reaction of magnesium with water

Magnesium does not react with water to any significant extent. This is in contrast with calcium, immediately below magnesium in the periodic table, which does react slowly with cold water. Magnesium metal does however react with steam to give magnesium oxide (MgO) (or magnesium hydroxide, Mg(OH)2, with excess steam) and hydrogen gas (H2).

Mg(s) + 2H2O(g) → Mg(OH)2(aq) + H2(g)

Reaction of magnesium with the halogens

Magnesium is very reactive towards the halogens such as chlorine, Cl2 or bromine, Br2, and burns to form the dihalides magnesium(II) chloride, MgCl2 and magnesium(II) bromide, MgBr2, respectively.

Mg(s) + Cl2(g) → MgCl2(s)

Mg(s) + Br2(g) → MgBr2(s)

Reaction of magnesium with acids

Magnesium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Mg(II) ion together with hydrogen gas, H2. Corresponding reactions with other acids such as hydrochloric acid also give the aquated Mg(II) ion.

Mg(s) + H2SO4(aq) → Mg2+(aq) + SO42-(aq) + H2(g)

Mg(s) + 2HCl(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g)

Reaction of magnesium with bases

Magnesium metal appears not to react with dilute aqueous alkalis.

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