Glycerol reacts with potassium manganate according to the equation below.
14KMnO4(s) + 4C3H5(OH)3(l)=> 7K2CO3(s) + 7Mn2O3(s) + 5CO2(g) + 16H2O(l)
When glycerol
is added to potassium manganate crystals a great deal of energy is released. The reaction proceeds at a faster rate when the potassium manganate crystals are finely crushed. This demonstration provides a good example of how the rate of a reaction is increased by increasing the surface area of reactant particles.
View the video on the right.
No extra heat is provided to inititiate the reaction. White smoke, steam
and a purple flame are generated after a short delay. The length of this
delay is proportional to how fine a powder the potassium manganate is.
Demonstration
Place 5g of KMnO4 (VII) crystals into a crucible, on a heat proof mat, as shown on the left. Place a few drops of glycerol on the surface using a dropper and stand well back.
Using a mortar and pestle, finely crush the crystals and repeat the procedure above.
What do you notice about the duration of the delay? Explain. Hint.
Safety
Potassium manganate reacts explosively with organic matter. The demonstration should be conducted in a closed fume hood as lumps of KMnO4 as well as flames can be ejected a long way from the source.
