Bromine

Bromine: the essentials

 Brief description: bromine is the only liquid nonmetallic element. It is a member of the halogen group. It is a heavy, volatile, mobile, dangerous reddish-brown liquid. The red vapour has a strong unpleasant odour and the vapour irritates the eyes and throat. It is a bleaching. When spilled on the skin it produces painful sores. It is a serious health hazard, and maximum safety precautions should be taken when handling it.

Cartoon by Nick D Kim (nearingzero.net, used by permission).

Isolation

Isolation: bromine is available commercially so it is not normally necessary to make it in the laboratory. Bromine also occurs in seawater as the sodium salt but in much smaller quantities than chloride. It is recovered commercially through the treatment of seawater with chlorine gas and flushing through with air. In this treatment, bromide is oxidized to bromine by the chlorine gas. The principle of oxidation of bromide to bromine is shown by the addition of a little chlorine water to aqueous solutions of bromide. These become brown as elemental bromine forms.

2Br^- + Cl₂ → 2Cl^- + Br₂

Small amounts of bromine can also be made through the reaction of solid sodium bromide, NaBr, with concentrated sulphuric acid, H₂SO₄. The first stage is formation of HBr, which is a gas, but under the reaction conditions some of the HBr is oxidized by further H₂SO₄ to form bromine and sulphur dioxide. This reaction does not work with the corresponding chlorides and fluorides.

NaBr (s) + H₂SO₄ (l) → HBr (g) + NaHSO₄ (s)

2HBr (g) + H₂SO₄ (l) → Br₂ (g) + SO₂ (g) + 2H₂O (l)

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