Cotton wool ball is ignited with a mixture of two substances placed on a glass rod end
name: Dehydration of permanganic acid with sulfuric acid
Chemistry experiment 48 - Manganese Heptoxide
Permanganic Acid / Manganese Heptoxide (fire)
Punjabi Science - Fire with chemicals 2
Wear lab gloves and eye protection.
There is a serious fire risk - a fire extinguisher should be ready.
Avoid contact of concentrated sulfuric acid with skin!
This experiment should be performed in a well-ventilated room or in a fume hood.
Always follow general safety
recommendations. Please note that conducting chemistry
experiments you must comply with the relevant legal procedures in
KMnO4 + H2SO4 → HMnO4 + KHSO4
HMnO4 → Mn2O7 + H2O
- Place two watch glasses and a cotton wool ball on a heat resistant mat.
- Pour 1-2 ml of concentrated sulfuric acid on the first watch glass.
- Put a spatula of potassium permanganate on the second watch glass.
- Moisten the end of a long glass rod in sulfuric acid, touch potassium permanganate with this end of the rod and then immediately touch the cotton wool ball. A few seconds later the cotton wool ball is ignited.
Two reactions simultaneously occur when potassium permanganate contacts with concentrated sulfuric acid. The first reaction is the protonation of MnO4 ions forming HMnO4. In this reaction sulfuric acid exhibits acidic properties.
In the second reaction unstable permanganic acid undergoes dehydration with concentrated sulfuric acid forming manganese heptoxide (Mn2O7). Thus sulfuric acid plays the role of a dehydrating agent.
Manganese heptoxide is a strong oxidizer and can ignite such organic matter as cotton.