Expt:Spontaneous exothermic reaction
From Learn Chemistry Wiki
Apparatus and chemicals
- Eye protection
- Safety screens
The teacher requires:
- Clean metal lid from a tin can or jar (see note 1)
- Heat resistant mat
- Access to (quantities of chemicals given are for one demonstration):
Potassium manganate(VII) (Oxidising agent, Harmful, Dangerous for the environment) Refer to CLEAPSS® Hazcard 81
- If the lid from a jar has a plastic lining, this should be scraped off. Alternatively, use a small foil cake case which has been cleaned and dried.
- Fine crystals of potassium manganate(VII) work much better than larger ones. Use a pestle to grind large crystals in a clean mortar, if necessary.
- Old samples of glycerol are sometimes ineffective, possibly because of absorbed water from the air.
Health & Safety
Wear eye protection throughout and use safety screens.
A. Put 2-3 g of potassium manganate(VII) in a small pile on the tin lid standing on the heatproof mat. Make a small hollow in the centre of the pile.
B. Pour about 1 cm3 of glycerol into the hollow in the pile of potassium manganate(VII).
It is sometimes better if the glycerol is warmed just before use. After about 20 seconds (but beware – it can be much longer), the mixture starts to give off steam. The glycerol in the mixture then ignites, burning with a bright, pinkish (lilac) flame for a few seconds more, leaving a dark brown or black residue.
This experiment has been reproduced from Practical Chemistry: http://practicalchemistry.org/experiments/spontaneous-exothermic-reaction,48,EX.html
This website has a movie showing the experiment 'Oxidation of glycerine by potassium permanganate': http://www.jce.divched.org/JCESoft/CCA/CCA1/R1MAIN/CD1R1870.HTM#1920