Bromine : Methods of Preparation

Bromine

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 Methods of preparation :

1.  By passing chlorine gas in aqueous solution of KBr or MgCl₂ :

2KBr +Cl₂  ———->   2KCl + Br₂

MgBr₂ + Cl₂ ———> MgCl₂ + Br₂

2. By the reaction of HCl with a mixture of KBr(potassium bromide) and KBrO₃(potassium bromate) :

5KBr + KBrO₃ +6HCl ———> 6 KCl + 3Br₂ + 3H₂O

3. By heating KBr or NaBr, MnO₂ with concentrated H₂SO₄:

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

or

2NaBr + MnO₂ + 3H₂SO₄ ———>  Br₂ +2 NaHSO₄ +MnSO₄ +2H₂O

Manufacture from Carnallite:

Carnallite is KCl.MgCl₂.6H₂O. Carnallite obtained from Stassfurt in Germany  also contains MgBr₂. Carnallite contains about 0.25% Br₂  in the form of MgBr₂. On concentrating the aqueous solution of carnallite , crystals of KCl separate out. The filterate contains MgCl₂ and MgBr₂. This  filterate is also called  mother liquor.

Hot mother liquor is sprayed from the top of tower which is packed with stone pieces. A mixture of chlorine gas and stream is passed from the bottom of the tower. Bromine is liberated from MgBr2 which is  present in the mother liquor.

MgBr₂ + Cl₂   ———-> MgCl₂ +Br₂

Vapours of bromine are drawn off from the exist and condensed. Vapours  which is not get condensed ,are taken into a chamber containing iron then it  reacts with iron and form ferrous bromide and ferric bromide. This mixture is used for the manufacture of KBr.

3Fe + 4Br₂ ——-> FeBr₂ + 2FeBr₃

when mother liquor is sprayed from the top, some liberated bromine dissolves in it and comes in recovery chamber. Bromine collected in recovery chamber is vaporized by steam. The vapours of bromine are  passed through the tower again and drawn off from the exist at the top of the tower and condensed.

Manufacture  of bromine  from sea water :

source : www.octelamlwch.co.uk

Sea water contains  KBr , MgBr₂  &  NaCl. Sea water is concentrated and made acidic and then Cl₂ is passed in it.

MgBr₂ +Cl₂  ———> MgCl₂ +Br₂

2KBr + Cl₂ ——-> 2KCl + Br₂

Bromine  dissolves  in hot water. Hot air is passed in water to vaporize Br₂. These  vapours are passed in hot aqueous solution of sodium carbonate. A mixture of NaBr & NaBrO₃  is obtained in solution.

Na₂CO₃ + Br₂ ——-> NaBr +  NaBrO₃ +CO₂

Solution containing NaBr and NaBr0₃ is treated with concentrated H₂SO₄ then bromine is obtained which is condensed and collected.

5NaBr +NaBrO₃ +6H₂SO₄ ——–> 6NaHSO₄ + 3Br₂ +3 H₂O.