This demonstration is an effective way to show that some reactions can produce light while the temperature of the solution remains constant. The chemicals, when mixed, produce a blue glow that can be made more obvious by lowering the main lights in the lab.
Equipment typically required (per demo):
- Household bleach 100cm3 (IRRITANT) This needs to contain sodium chlorate(I) (sodium hypochlorite - NaOCl) and NOT hydrogen peroxide. Select a cheap bleach which does not contain thickeners or added fragrances. It should be a 5% 'available chlorine' solution.
- Luminol (3-aminophthalhydrazide), 0.4 g (IRRITANT)
- Sodium hydroxide pellets, 4.0 g (CORROSIVE)
- Digital balance
- 2l beaker
- 2x 1 litre conical flasks with bungs
- Eye protection
A technician will need to make up the solutions in advance of the lesson.
Firstly, 100ml of the bleach is mixed with 900ml of water in one of the flasks. This is mixed thoroughly. Place a bung in the flask.
Mix 1000ml of water with 0.4g of luminol and 4g of the sodium hydroxide pellets in the other flask. Some of the luminol may remain unmixed, this is normal. Place a bung in the flask until needed.
If a small amount of fluorescein is added to the luminol solution, the reaction will produce a yellow glow instead of blue.
The two solutions are ready to be mixed. They should be poured into a beaker at the same rate. With dimmed lights you should be able to see a blue glow being emitted from the mixture. This will only last for a few seconds.