|Name: bromine||Group number: 17|
|Symbol: Br||Group name: Halogen|
|Atomic number: 35||Period number: 4|
|Atomic weight: 79.904 (1)||Block: p-block|
|CAS Registry ID: 7726-95-6||Voice: |
|Standard state: liquid at 298 K||Colour: red-brown, metallic lustre when solid|
|Classification: Non-metallic||Availability: |
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of bromine.
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)