In this experiment we are going to make fluorescent toothpaste.
This experiment is suitable as a demonstration of chemistry in reactions that need to be eye-catching. It is not a suitable experiment for children to play with. Only for what they see.
WHAT IS FLUORESCENT ELEPHANT TOOTHPASTE?
It is a well-known experiment as it generates a very colourful reaction, as a column of foam shoots out. This foam comes from the decomposition of hydrogen peroxide when it is mixed with soap. While the materials used in the experiment are dangerous (highly concentrated hydrogen peroxide can be very corrosive), the resulting foam, which is nothing more than oxygen mixed with soap, is not. In addition, to make the experiment more participatory for children, we use fluorescent dye, sodium fluorescein, which, when illuminated with ultraviolet torches, will give the experiment a fluorescent colour.
MATERIALS FOR THE EXPERIMENT
Hydrogen peroxide 30% or 110 volumes. Available in pharmacies
- Potassium iodide
- Fluorescein sodium
- Liquid soap (normal kitchen soap, such as Mistol or Fairy).
- Ultraviolet light torches
STEP-BY-STEP EXPERIMENT
- Take an elongated glass or measuring cylinder and add 10-15ml of hydrogen peroxide.
2. Add the drops of dish soap.
3. Add the sodium fluorescein to fluoresce the fluorescent colour.
4. Add the potassium iodide and the reaction starts instantly.
ON VIDEO
TECHNICAL EXPLANATION OF THE EXPERIMENT
Hydrogen peroxide is a compound that naturally decomposes into water and oxygen, according to the following reaction:
2 H2O2(aq) → 2 H2O(l) + O2(g)
This reaction, however, is slow, and to speed it up we use potassium iodide, KI, which, although it is not consumed in the reaction, will help to quickly decompose the hydrogen peroxide, creating almost instantaneously a large amount of oxygen, which when it comes into contact with soap forms a dense foam that expands.
The reaction we will therefore have is
H2O2(aq) + I-(aq) → OI-(aq) + H2O(l)
H2O2(aq) + OI-(aq) → I-(aq) + H2O(l) + O2(g)
As can be seen, the iodide ion that goes into the first reaction also comes out as a product in the second reaction, which means that it catalyses (speeds up) the reaction, but is not consumed in the process.