“Fire picture” experiment
How to make a paper drawing smolder
How can you burn a picture onto paper using a chemical reaction? In this simple experiment, we’ll show you how!
Wear protective gloves and glasses. Observe safety rules when working with fire and flammable objects.
Reagents and equipment:
- saturated solution of potassium nitrate;
To prepare the saturated solution of potassium nitrate, dissolve 50 g of salt in 40 ml of hot water. Then apply the solution to the paper in a thick layer with a brush. Leave the “drawing” for 20 minutes, so that it dries (drying time depends on the temperature in the room). Then touch the “drawing”. Watch the picture appear!
Potassium nitrate or saltpeter is a strong oxidizer in both solid and liquid state. It is found in gunpowder and fireworks, and used as fertilizer. When potassium nitrate is heated above 400 ⁰C, it starts to break down and release oxygen, which reacts with the paper.
Paper (cellulose) burns more quickly than from the oxygen in the air, but it does not burn to the end, as oxygen and the reaction temperature are not sufficient for complete combustion. The reaction products are carbon dioxide, water, charcoal and ash:
2КNO₃ = 2KNO₂ + O₂
nКNO₃ + (C₆H₁₀O₅)n = nKNO₂ +nН₂О + nС+ nСO₂
A similar experiment is included in the “Nitrogen” set — see Fire label.