. Explain the preparation of Iodine


Best Answer

i. From chile saltpetre (caliche):

The main source of iodine is NaIO3 (sodium iodate) which is found in nature with NaNO3 (chile saltpetre). NaIO3 is present in small amount. After crystallisation of NaNO3 , the mother liquor left contains NaIO3  (soluble). To this solution NaHSO3 is added where upon I2 is precipitated

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ii. From sea-weeds :

Certain marine plants absorb and concentrate I– selectively in presence of Cl– and Br–. Sea-weeds are dried and burnt in shallow pits, ash left is called kelp. Ash on extraction with hot water dissolves out chlorides, carbonates, sulphates and iodides of sodium and potassium. The solution on concentration separates out all leaving behind iodide in the solution. Solution is mixed with MnO2 and concentrated H2SO4 in iron retorts. Liberated iodine is condensed in series of earthenware known as aludels.

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