Demonstration of Iodine

Chemicals needed

potassium iodide

sulphuric acid 96%  GSATZEND.gif (935 Byte) C    R 35   S (1/2)-26-30-45

Equipment necessary

test tube

Test procedure


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.


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


Iodine vapors rise


to be added.