Surprise your students by soaking a piece of paper (or an old £5 note) in a mixture of ethanol and water and igniting it
In this experiment, students observe as a piece of paper (or an old bank note) is soaked in a mixture of ethanol and water. When the mixture is ignited, the ethanol burns but the paper does not.
This demonstration can either be used for fun as part of a public event or in a class to stimulate discussion of the conditions required for combustion.
- Eye protection
- Bunsen burner
- Pair of tongs
- Heat resistant mats, x2
- Beakers, 250 cm3, x3
- Paper, eg filter paper (see note 6 below)
- Ethanol (HIGHLY FLAMMABLE) or Industrial Denatured Alcohol (IDA) (HIGHLY FLAMMABLE, HARMFUL), 75 cm3
- Sodium chloride (common salt), about 1 g
Health, safety and technical notes
- Read our standard health and safety guidance.
- Wear eye protection throughout.
- Ethanol, C2H5 OH(l) (HIGHLY FLAMMABLE) – see CLEAPSS Hazcard HC040A.
- Industrial denatured alcohol (IDA) (HARMFUL, HIGHLY FLAMMABLE) – see CLEAPSS Hazcard HC040A.
- Sodium chloride, NaCl(s) – see CLEAPSS Hazcard HC047b.
- Prepare some pieces of absorbent paper, eg filter paper, about the size of a £5 note.
- Place about 50 cm3 of water in one beaker, a similar volume of ethanol in a second beaker, and a mixture of 25 cm3 water and 25 cm3 ethanol in the third beaker. Add a little (about 1 g) of sodium chloride to the third beaker and stir until it has all dissolved. Label the beakers.
- Polymer based notes (such as the new £5 and £10 sterling note, issued in 2016 and 2017) have been coming into circulation in a variety of countries. We advise only ‘paper’ based notes are used for this experiment. Polymer based notes will not burn in the same way as paper versions and are not suitable for this experiment.
- Label the beakers.
- Place the Bunsen burner on the heat-resistant mat and adjust it to give a yellow flame. Ensure that the beakers of ethanol, water, and the ethanol-water mixture are a safe distance (2 m) away from the Bunsen burner.
- Using the tongs, soak one piece of paper in the water in the first beaker. Allow the paper to drain. Try to ignite it by holding it in the Bunsen flame for a few seconds. It does not ignite.
- Soak a second piece of paper in ethanol and use the tongs to hold it in the Bunsen flame just long enough for it to ignite. Take care to drip as little alcohol as possible on the bench between the beaker and the Bunsen burner. The alcohol on the paper ignites easily and sets fire to the paper, which burns away. (If the alcohol in the beaker does ignite by accident during the demonstration, it can be easily and safely extinguished by covering the beaker with a heat-resistant mat.)
- Soak the third piece of paper in the alcohol-water mixture and use the tongs to hold it in the Bunsen flame just long enough for it to ignite. Swiftly remove the paper from the Bunsen flame and observe as the alcohol burns with a yellow flame, but the paper does not burn. The paper will still be wet with water after the alcohol has burnt away.
The demonstrator can start this experiment with an old £5 note if available. It is important to use a yellow Bunsen flame, and to only hold the paper in the flame long enough for it to ignite, to prevent the note from burning. The demonstrations with ordinary paper and the other liquids could then follow to provide an explanation.
The water in the alcohol-water mixture evaporates as the alcohol burns, keeping the temperature of the paper below its ignition temperature (approximately 230 °C). Converting this temperature to the Fahrenheit scale can also allow for a discussion of the use of this scale and for the ‘keen’ science fiction fans a discussion about the novel and film Fahrenheit 451.
The flame from the paper soaked in alcohol alone should be visible but the flame from a burning alcohol-water mixture is often difficult to see. This is why the sodium chloride is added, to give an orange-yellow colour to the flame. The demonstration looks even more impressive in subdued lighting.
This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany Practical Physics and Practical Biology.
The experiment is also part of the Royal Society of Chemistry’s Continuing Professional Development course: Chemistry for non-specialists.
© Nuffield Foundation and the Royal Society of Chemistry