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Bromine

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BROMINE

Bromine is a halogen element belonging to the group VII of the periodic table. it is a reddish brown coloured liquid. It is characterised by

     

  1. Atomic number 35

    2.  

  2. Relative atomic mass 79.909

    3.  

  3. Melting point -7.2OC

    4.  

  4. Boiling point 58.78OC

    5.  

  5. It has an irritating bad odour.

    6.  

  6. It is fairly soluble in water

    7.  

  7. It is excessively soluble in organic solvents.

PREPARATION

     

  1. In the laboratory bromine is prepared by passing chlorine vapours are through a solution of potassium or magnesium bromide,

    2. MgBr2 + Cl2 è MgCl2 + Br2

    KBr + Cl2 è 2KCl + Br2

     

     

  2. Commercially it is prepared from sea water. The sea water is first acidified and then saturated with Cl2 to effect the reaction

Cl2 + Bromides è Chlorides + Br2

After the treatment with chlorine, air is bubbled through the solution, sweeping out the bromine, which is then absorbed in aqueous sodium carbonate solution to give a mixture of bromate ion and bromide ion. When this solution is subsequently acidified, bromine is once again produced :

6H+ + BrO3- + 5Br- è 3Br2 + 3H2O

Bromine is now obtained by distillation.

CHEMICAL PROPERTIES

     

  1. Oxidising action

Bromine is a good oxidising agent

     

  • In the presence of an oxidisable agent it forms hydrogen bromide

Br2 + H2O è 2HBr + O

Oxidisable substance(A) + O è AO

  • It oxidises sulphur dioxide into sulphuric acid

SO2 + Br2 + 2H2O è 2HBr + H2SO4

NOTE: Bleaching action

Bromine shows a bleaching property similar to that of chlorine, although it is weaker. The bleaching action of bromine is due to its oxidising property.

     

  1. With alkalies it forms a hypobromite in cold dilute solution and a bromate in a hot solution

    2. 2KOH + Br2 è KBr + KBrO + H2O

    Cold and dilute

    Potassium hypobromite

     

    6KOH + 3Br2 è 5KBr + KBrO3 + 3H2O

    hot and concentrated

    Potassium bromate

  2. with organic compounds it forms addition compounds

C2H4 + Br2 è C2H4Br2

USES

  1. One of the main uses of bromine is in the manufacture of ethylene bromide.

  2. Also it is used in the manufacture of NaBr and KBr

  3. It is used as a germicide and fungicide

  4. It is used as an oxidising agent

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