Introduction

Organic solvents with densities greater than and less than that of the aqueous solution are used to extract the iodine.

The aqueous solution of food color is blue.  Iodine in water is yellow, and when added to the food color the result is a green solution. When this aqueous solution is extracted with organic solvents (hexane and dichloromethane), the iodine is drawn into the organic layer, leaving a blue aqueous layer and turning the organic layer purple. The hexane layer (d=0.66g/mL) will float on top of the aqueous, while the dichloromethane (d=1.33g/mL) will settle beneath the aqueous.

To Conduct Demonstration:  

  1.  Pour solution of blue food color  into one test tube to a depth of 2".
  2. To one of the tubes containing the mixed solution, add two inches of hexane. Stopper with a cork and shake to mix.
  3. To one of the tubes containing the mixed solution, add two inches of dichloromethane. Stopper with a cork and shake to mix.
  4.  Place the test tubes in a lighted rack. Compare the colors and identify the layers.

Safety 

Take care not to get solutions on skin. Gloves are suggested, but will not keep out dichloromethane. Release pressure often during extractions.