Dr. Márta Rózsahegyi

Oxidation effect of potassium-nitrate

There are many interesting experiments in lab manuals to show the oxidation effects of nitrates (1, 2). Maybe the best method to show this effect is reaction of KNO3 and S because of its reaction heat (3). The execution of reaction is very simple and doesn’t claim much preparations.

Chemicals: potassium-nitrate, sulphur powder

Tools: test tube, test tube catch, ironstand, Bunsen burner, chemical spoon, balance, watch-glass, sand, platter

Weight on a scale 7 g KNO3 and 3 g sulphur powder. Mix them up on a watch-glass and pour the mixture into a test tube. Grip the test tube in the ironstand and put it under hood. Put a platter, in which there is sand, under the test tube. Heat the bottom of the test tube with the Bunsen burner. The two solid materials will be melted. When a flash appears in the test tube, stop heating.

KNO3 is a very strong oxidizing agent, it was a component of black gunpowder. This compound is decomposed by heat. Oxygen originates from KNO3 and oxidizes sulphur. The reaction is exotermic. Glass, which becomes softer at 6-700 °C, is melted by reaction heat. Sulphur-dioxide is poisonous and smells penetrating bad, that’s why experiment should be made up under hood.

1. Dr. Lengyel Béla: Általános és szervetlen kémiai praktikum (Tankönyvkiadó, Budapest, 1990.) - in Hungarian
2. Rózsahegyi Márta-Wajand Judit: 575 kísérlet a kémia tanításához (Tankönyvkiadó, Budapest, 1994.) - in Hungarian
3. Januschewsky Jarisch: Chemie 1. (Verlag Braumüller, Vienna, 1983.)