Ask A Scientist© Chemistry Archive

 >>    name         dan powers
 >>    status       student
 >>    age          40s

 >>    Question -   how do i make iodine crystals?
 >
 >

Hi Dan...there are many ways to obtain Iodine crystals.
it will depend of the purity you will need and if you
want to prepare the Iodine first and then proceed to
crystalize it. The Iodine is a substance that sublimes easily,that means
that once the crystals are formed
they will pass even at room temperature to gaseous
state quickly and directly without going into a liquid
state instead.So in order to keep your crystals you
will need an extra special care.
Ok, lets see an easy experiment supposing you want
to prepare the Iodine first:
You will need:
Bunsen burner and asbestos square (or a hot plate)
Tripod and tin lid
Beaker, 250 ml
Separating funnel 100ml
Evaporating dish

Hydrogen peroxide 20 volume
Tetrachloromethane or dichloromethane
Distilled water
1M solution of Sulphuric acid
Supply of ribbon seaweed(Laminaria) - that you can
obtain a a biological supply store or from the
sea shore

Procedure
(You must work at a fume cupboard)
1-Collect and dry about a dozen 50cm lenghts of the
seaweed and heat them strongly on a tin recipient
until they are reduced to ash; probably it will
reduce a quite small quantity, about a spoonful.
2- Add to the ash   20 ml of distilled water
in a beaker, and heat the suspension until it boils.
3 - Filter the suspension
4 - Acidify the filtered with  Sulphuric acid solution
5 - Add then the hydrogen peroxide solution
     You will observe the formation of a brown color due
     the iodine liberation from the iodine ions present
6- Transfer the mixture to a separating funnel
7 -Extract the Iodine with tetrachloro methane or other
    solvent. The result is an organic solution of iodine.
8 - In order to obtain crystals , the solvent may be
     allowed to evaporate at room temperature, by
     placing it in an evaporating dish in a fume cupboard.
     It will result  crystals of iodine or rather gray-
     black brilliant flakes.

Hope that satisfies you. If you need a more sofisticated
method, with a purifying step, just ask again.
Mabel
(Dr. Mabel Rodrigues)


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