Presentation of aluminium(III)-iodide

Chemicals needed

aluminium grits F R 15-17 S (2)-7/8-43

iodine Xn N R 20/21-50 S (2)-23-25-61

Equipment needed

test tube
test tube holder
burner (gas or alcohol)

Test procedure

Safety goggles. With larger amounts there is the danger of explosion! Although the experiment has been carried out several times and proven itself harmless, one shoud point the test tube away from people.
One adds a small(!) spatula-tipful aluminium grits to the test tube and adds about twice its volume in small pieces of iodine.
Now one warms the mixture with the burner. After the iodine has begun to melt and to vaporize, particles of aluminium begin to glow brightly here and there. A white coating of aluminium iodide forms a bit over the test tube bottom, higher up iodine vapor solidifies in the range of violet to black.

Disposal

The diluted residues can in the case of small quantities be discharged into the drainage. If one adds water to the cooled mixture a hissing noise results: the irreversible hydration of the anhydrous aluminium iodide is intensely exothermic (one compares the reaction of AlCl3).

Elucidation

This is a case of oxidation with flame phenomenon(combustion), whereby not oxygen but iodine serves as the oxidant. The reaction with oxygen should, in accordance with its oxidizing effects, be substantially more powerful, however aluminium (except in the finest of distributions) is difficult to ignite under air. This is due to the fact that the Al2O3 which is formed on the surface hinders the reaction. AlI3 on the other hand sublimates already at relatively low temperatures and supplies ever new aluminium metal for the reaction's progress.

Photos

to be added

Literature