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Name: dan powers
Status: student
Age: 40s
Location: N/A
Country: N/A
Date: Around 1999

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.

(Dr. Mabel Rodrigues)

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