Explosive Manganese

Manganese heptoxide, a highly reactive green liquid, is made by mixing solid potassium permanganate with concentrated sulphuric acid.

Make and Test Manganese Heptoxide

How to make Explosive Manganese

  1. Take a very small amount of potassium permanganate (a really small pinch at the end of a spatula), somewhere between 10 and 20 mg. Do not use larger quantities.

  2. Put a few drops of concentrated sulphuric acid on the potassium permanganate, such that all solid is covered. Do not use too much acid. That might make the permanganate too dilute.

  3. Let the acid act on the solid potassium permanganate for half a minute. A dark green liquid is formed, with a somewhat oily appearance.

  4. Take a glass rod and put a single drop of acetone or other combustible liquid on the tip. This can be done easily by putting some of the liquid in a small test tube (0.5 ml or so) and keeping it almost horizontally. Then put the glass rod in the liquid, such that quite a large part of it is wetted. Then take it out of the test tube and keep it at an angle of around 45 degrees. A nice small drop collects at the tip of the rod. Carefully touch the dark green liquid with the tip of the rod. 

Why is Manganese Heptoxide so unstable?

Potassium permanganate reacts with concentrated sulphuric acid as follows, manganese heptoxide being formed in the reaction:

  2KMnO4 + 2H2SO4 → Mn2O7 + 2KHSO4 + H2O

The green color is due to dissolved Mn2O7 in concentrated sulphuric acid. A very thin layer of this compound looks red/purple and the vapor of this compound is purple.

Manganese heptoxide is very unstable. It slowly decomposes, giving MnO2 and highly active oxygen. A simplified balanced equation is given below:

  Mn2O7 → 2MnO2 + 3[O]

When no combustible compounds are present, then plain oxygen and ozone are formed very slowly. When a combustible compound is present, then the released active oxygen is capable of igniting the combustible material at once. This reaction is very violent and often leads to explosive decomposition of remaining manganese heptoxide.

The brown smoke, released in the beginning of the experiment is finely divided MnO2, in a later stage, when the material cools down somewhat, it does not decompose anymore and the purple vapor of Mn2O7 can be observed.

Safety

  • Sulfuric acid is very corrosive
  • Potassium permanganate is a strong oxidizer
  • The formed compound is extremely dangerous. Contact with a combustable compound will instantly result in a vigorous exothermic reaction.

The use of this instruction and the information provided therein takes place at the user’s own risk.

Experiment Video