How to Make Iodine Crystals

Iodine is found in many compounds today and also occurs naturally in seaweed. You can extract small amounts of iodine crystals from seaweed in the laboratory as a chemistry experiment. This method isn't used commercially due to the relatively low concentration of iodine in seaweed. You'll need to store the iodine in an airtight container as soon as you isolate it or it will sublimate into the air.

Things You'll Need

• Ribbon seaweed
• Tripod with tin receptacle and lid
• Bunsen burner
• Asbestos square
• 2 250-ml Beakers
• Distilled water
• Filter paper
• 20-ml sulfuric acid
• 20-ml Hydrogen peroxide solution
• 100-ml Separating funnel
• 20-ml tetrachloromethane
• Evaporating dish

Instructions

1. Obtain approximately 12 pieces of ribbon seaweed about 20 inches in length. Ribbon seaweed is available at biological supply stores and you may also be able to collect it at the beach. Allow the seaweed to dry thoroughly and place the strips in a tin receptacle under a fume hood.

2. Cover the receptacle with the lid and place heat the receptacle under with the Bunsen burner until the seaweed is reduced to ash.

3. Place the ash in a 250 ml beaker and add 20 ml of distilled water. Heat the beaker with the Bunsen burner until the water boils. Pour this solution through a layer of filter paper into another beaker. Add 20 ml of sulfuric acid and 20 ml of a hydrogen peroxide solution.

4. Pour the contents of the beaker into a separatory funnel and add 20 ml of tetrachloromethane. Hold the stopper closed and shake the funnel vigorously. Pull the stopper open and open the stopcock valve to drain the bottom layer of the solution into a beaker.

5. Pour the contents of the beaker into an evaporating dish and place it under the fume hood. Allow the solution to evaporate at room temperature to produce gray-black crystals of iodine.

References

• Newton