Demonstration of Iodine

Chemicals needed

potassium iodide

sulphuric acid 96% C R 35 S (1/2)-26-30-45

Equipment necessary

test tube
lighter

Test procedure

Safety goggles! Ventilation or exhaust hood!
One adds 2-3 drops of concentrated sulphuric acid to a small spatula-tipful of potassium iodide in a test tube.
During foaming brown gases develop. Now briefly heat with a lighter.
During heating a violet vapor develops, which then precipitates blackly and firmly onto the test tube.

Disposal

One can dispose of this small quantity of the diluted (caution!) reaction mixture into the drainage. Better it would be to beforehand reduce the iodine to iodide, e.g. through sodium sulphite.

Elucidation

In contrast to chloride iodide acts reductively on sulphuric acid. Therefore hardly any hydrogen iodide is formed, but mainly elementary iodine, as well as sulphur dioxide. The brownish colorings are most likely due to iodine which has been dissolved in water.

2H2SO4 + 2 KI --> I2 + K2SO4 + 2H2O + SO2

Photos

Iodine vapors rise

Literature

to be added.