In this experiment, the combustion of two most common alcohols, methanol (CH3OH) and ethanol (C2H5OH), is demonstrated. These alcohols are also used also as motor fuels. In laboratories, ethanol is used both as a solvent and as the combustible substance in ethanol burners.
1) In the first experiment, the combustion of ethanol was shown in a miniature ethanol burner and also in an open porcelain vessel. The ethanol flame is almost colorless, the combustion products are carbon dioxide and water vapor:
C2H5OH(l) + 3O2(g) → 2CO2(g)+ 3H2O(g)
2A) Reaction of potassium permanganate (KMnO4) and sulfuric acid (H2SO4):
2KMnO4(s) + H2SO4(l) → K2SO4(s) + 2HMnO4(l),
2B) Formation of a very strong oxidizer - manganese(VII) oxide (Mn2O7):
2HMnO4(l) → Mn2O7(l) + H2O(l)
Attention! Avoid contact of concentrated sulfuric acid (especially the mixture of sulfuric acid and KMnO4) with clothes and skin!
2C) Mn2O7 ignites methanol vapors in the conical flask:
2CH3OH(g) + 3O2(g) → 2CO2(g)+ 4H2O(g)
3) In the last experiment, some methanol - a very volatile alcohol - was sprayed into a cardboard cylinder. The mixture of methanol vapors and air was ignited. The expanding gases (CO2, H2O as water vapor) from the combustion of methanol propelled the plastic cylinder up from the cardboard cylinder. This experiment fits well to model the movement of the piston in the cylinder of an internal combustion engine.
Wider use of methanol is limited by its toxicity.