Why Potassium Per-Maganate Burns With Glacerol/Glacerin?

You will enjoy making fun of it doing experimental at schools as a practical work.

Just do it!

First of all set the watch glass or bowl on the cork base, and have the blast shield in front of it. Use the Cup to put a small pile of potassium permanganate (KMnO4) in the middle of the dish, and make a small indentation in the center of the pile.

What is KMnO4 ? Introduce redox reactions.

Did you know for ideas on what they think will happen when you add the glycerin/glycerol to the bowl?

KMnO4 is the chemicals substances which derive from the combination of Potassium(K) and Manganese(Mn) in the present of atmospheric Oxide(O).

Put a small drop of the glycerin/glycerol into the dish, in an indentation of the pile. Immediately go into the following explanation:

When KMnO4 mixes with glycerin/glycerol, a redox reaction starts. This reaction starts out really slow, but produces a lot of heat, so it will start to speed up bit by bit. As the KMnO4 oxidizes the sugar, it will speed up more and more until it finally starts to smoke, and after that it will ignite burning.

The reaction takes 10-15 seconds to ignite, depending on outside temperature and the temperature of the glycerin/glycerol. If timed carefully, the reaction will start smoking when you say “until it finally starts to smoke”, and then ignite 1-2 seconds later!

You might have ask if they can guess why it starts ignite slowly?

You can draw a reaction equation on a whiteboard, and point out the large amount of KMnO4 needed to start the reaction.

Reduction-Oxidation Reactions, or Redox Reactions, are reactions that involve a transfer of electrons(e). Oxidizers such as Potassium Permanganate (KMnO4) take electrons, while Reducers such as Glycerin and Glycerol giving electrons. When electrons are transferred between the reactants, it is usually by the transfer of oxygen atoms. This means that our glycerin/glycerol is Oxidized, or our KMnO4 is Reduced.

Then one can see it as glycerin would receive oxygen atoms from the KMnO4. The KMnO4 is then “reduced”, losing oxygen atoms, while the glycerin is “oxidized” or gains oxygen atoms.

The reaction between KMnO4 and Glycerin goes as follows:

14 KMnO4 + 3 C3H8O3 ⇒ 14 MnO2 + 7 K2CO3 + 2 CO2 + 12 H2O

This reaction requires a large amount of KMnO4 for it to progress. This is part of why the Rate of Reaction, or time it takes a reaction to complete, is slow for this particular reaction. The rate of reaction can be affected by a large number of factors, such as the temperature, the amount of each reactant, and how well the reactants are mixed. This is explored with the two methods of presenting this demonstration.

In the Primary Method, we rely on the slow rate of the reaction to get the dramatic effect for the presentation. The glycerin is poured onto the KMnO4 powder, and they start to react. However, it takes time for it to react, since the glycerin absorbs much of the heat generated. The reaction creates a lot of heat, which is why it ultimately results in a bright flash of sparks. But it takes time for it to create the heat, and so the presenter has time to provide an explanation of the steps in the reaction. Once it starts to smoke, the smoke helps to carry away the produced water vapors and carbon dioxide, as well as any waste carbon produced in the burning of glycerin.

Then, when it ignites, the whole pile will react quickly, having a large amount of extra heat to push the reaction along.

In the Alternative Method, we are showcasing how the mixing of the reactants affects the rate of reaction. One of the watch glasses has the reactants in direct contact, while the other has the reactants next to each other. As is expected, the reactants that are in-direct contact will ignite much faster than the ones which are not.

The physical chemistry of a reaction is important when it comes to the reaction’s pace, and if the reactants are never mixed, they will have no reason to react, and it may not burn as a whole process.

Try it by yourself hope you will find the best proof of your understanding.

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