Iodine is the least reactive compared to the other common halogens (it is
more reactive than the rare and radioactive halogen Astatine. Similarly to
Bromine, also Iodine is obtained from seawater or from the reduction of sodium
iodate (V). In the laboratory, however, it can be produced useing the same
method as Bromine: if an iodide salt is reacted with sulphuric acid, this
produces hydrogen iodide, which can then be oxidized by manganese (IV) oxide to
give Iodine.
Test for Iodine:
Unlike the other halogens, Iodine does not bleach litmus paper.
If a starch solution is added to an aqueous iodide solution, it will
change to a blue-black which neither chlorine nor bromine will do.
When silver nitrate is added to Iodine, it forms an insoluble compound.
Therefore, if Iodine is present a yellow precipitate is formed in this
reaction.
Uses of Iodine:
Manufacture of photographic film: Even though this element is not
widely used, it is a main component in photography due to its sensitivity to
light and due to its unreactive nature (Chlorine may become dangerously
explosive when reacted with another element in light). As a result it is
used extensively in the manufacture of photo films.
