Potassium permanganate
A curious reaction occurs upon addition of concentrated sulfuric acid to potassium permanganate. Concentrated sulfuric acid reacts with KMnO4 to give Mn2O7, which can be explosive. Although no reaction may be apparent, the vapor over the mixture will ignite paper impregnated with alcohol. Potassium permanganate and sulfuric acid react to produce some ozone, which has a high oxidizing power and rapidly oxidizes the alcohol, causing it to combust. As the reaction also produces explosive Mn2O7, this should only be attempted with great care.