Question

Describe with diagram any one method of manufacture of iodine or bromine.

Answer 1

In laboratory, iodine can be prepared by the oxidation of iodide salt with an acid in the presence of oxygen. This can be achieved by using either concentrated sulphuric acid or acidic solution of hydrogen peroxide as the oxidising agent. The reaction is as follows:

Using conc. sulphuric acid: $2I^{-}+4H^{+}+O_2\to I_2\downarrow +2H_{2}O$

1. Dissolve iodide salt ($NaI$) in minimum of water and cool the solution by keeping it into an ice bath.

2. Add concentrated sulfuric acid with continuous stirring. Along with iodine, other gases such as $HI$, $S{O}_2$, $H_{2}S$ and sulphuric acid vapours also form.

3. Keep adding the acid till the mixture turns from a paste to liquid state.

4. Pour the liquid mixture into ice-cold water and stir. Keep the mixture undisturbed for about ten minutes.

5. Solid iodine will settle at the bottom of the solution.

6. Rinse the solid multiple times to get rid of acid.

7. Iodine solid thus obtained can be purified further by crystallization. For this, purpose, a round-bottom flask, filled with ice, is kept above the beaker containing solid iodine. Upon heating the setup, the iodine vapourises and gets deposit at the bottom of the flask.

Thus obtained iodine is pure.