Bromine

Bromine, Br, is a red volatile liquid at room temperature, having a red brown vapour and a member of Group VIIb (i.e. the Halogen Group of elements) of the periodic table.

Atomic Number : 35
Atomic Mass : 79.909
Melting Point : -7 degC
Boiling Point : 58 degC
Density : 3.1

It forms compounds in which its oxidation states is 1, 3, 5, or 7.
The liquid is corrosive and harmful to human tissue and bromine vapour irritates the eyes and throat.

Discovery

Bromine was discovered by A J Balardin 1826AD, by the action of Chlorine on the residues (i.e. Bromide salts) after the crystallisation of the salt from the salt-marshes of Montpellier.


		NaBr    +    Cl2    ==>    NaCl    +   Br2

Balard also demonstrated that the liquid was an element and he suggested the name Bromine (Greek, stench) for the liquid.

Occurrence

Because of its reactivity, Bromine does not exist in the free elemental state in nature, but small quantities are combined in many silver ores.
Compounds of Bromine also occurs in marine animals and plants.
Bromide salts are found in seawater and in the salts deposits in Strassfurt.

Extraction

Bromine occurs primarily as bromide salts (e.g. Sodium Bromide, NaBr) in sea-water. On passing a stream of chlorine gas through a solution containing Bromide Ions, Br(-), free elemental bromine is released.


	2 Br(-)   +   Cl2   ==>   Br2   +   2 Cl(-)

Preparation

Bromine can be prepared in the laboratory by heating Potassium Bromide, KBr, with dilute Sulphuric Acid, H2SO4, and Manganese Dioxide, MnO2.


           2 KBr   +   MnO2   +   3 H2SO4	==>   Br2   +   2 KHSO4   +   MnSO4   +2 H2O

Manufacture

Bromine is manufactured industrially by allowing a solution of Potassium Bromide to flow down a tower, against a stream of Chlorine gas rising up through the tower.


	     2 KBr   +    Cl2    ==>    Br2   +    2 KCl

Properties

Bromine is a volatile dense mobile reddish-brown liquid, which readily gives a brown toxic vapour with a disagreeable irritating odour.
Bromineresembles Chlorine in many of its properties, but it is less reactive.
A solution of Bromine in water is called Bromine Water, which is used as a test reagent in organic chemistry to identify unsaturated compounds.
Bromine combines directly with most elements although heat or a catalyst is often necessary to start some reactions.
```
	                H2   +   Br2   ==>   2 HBr	

		2 Na   +   Br2   ==>    2 NaBr	
```
Bromine reacts with water to form a mixture of Hydrobromic Acid, HBr, and Hypobromous Acid, HBrO.
```
		Br2   +   H2O   ==>   HBr   +   HBrO	
```
Bromine liberates Oxygen when the resulting solution is heated or exposed to strong sunlight.
```
		2 HBrO   ==>   2HBr   +   O2	
```
Bromine reacts with alkalis in a similar way to Chlorine. Bromine also displaces free elemental Iodine from solution of Iodide Salts, I(-).

Reactions

Uses

Bromine is used in a vide range of industries :

in the manufacture of 1,2-DibromoEthane, CH2BrCH2Br, which is used as a petrol additive to prevent lead being deposited in the cylinders (i.e. from the anti-knock agent, Tetra-Ethyl Lead, Pb(C2H5)4),
in the manufacture of compounds used in photography (e.g. Silver Bromide, AgBr, which is the light sensitive material in film),
in the manufacture of dyestuffs and drugs,
in the analytical laboratory in testing for unsaturation in organic compounds, where bromine adds across the multiple bonds of unsaturated compounds,
as a disinfectant, adsorbed in sticks of a diatomic brick,
in making dyes, and
in gold extraction

Detection and Analysis

Bromine is detected by the brown colour of its vapour, and by its action on Iodide salts, (e.g. Sodium Iodide, NaI), which are oxidises to free elemental Iodine.


		2 NaI    +    Br2    ==>   2 NaBr    +     I2

The Iodine liberated in this reaction turns starch indicator solution to a blue colour.

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