Chemiluminescence of luminol – a cold light experiment
A solution of sodium chlorate(I) oxidises an aqueous solution of
(3-aminophthalhydrazide). The reaction gives out a blue luminol glow without any increase in temperature of the mixture. chemiluminescent
This demonstration experiment shows that a chemical reaction can give out energy as light instead of heating up its surroundings. The demonstration can also be used to stimulate interest in chemistry at an Open Day or other public event.
The teacher will require:
Conical flasks with stoppers (1 dm
Beaker (2 dm
Thermometer (0 – 100 °C)
Balance (1 d.p.)
Quantities of chemicals for one demonstration:
Household bleach 100 cm
3 OR sodium chlorate(I) solution (up to 14%) (CORROSIVE / IRRITANT) (Notes 1, 2 and 3)
Luminol (3-aminophthalhydrazide), 0.4 g (IRRITANT)
Sodium hydroxide pellets, 4.0 g (CORROSIVE)
Fluorescein (or sodium fluorescein) powder (optional)
Refer to Health & Safety and Technical notes section below for additional information.
Health & Safety and Technical notes
Read our standard health & safety guidance
Wear eye protection. Goggles should be worn when preparing the solution.
8H 7N 3O 2(s), (IRRITANT) - see CLEAPSS Hazcard and CLEAPSS Recipe Book.
Household bleach, NaOCl(aq), (IRRITANT) - see CLEAPSS Hazcard.
Sodium chlorate(I) solution, NaOCl(aq), (CORROSIVE) - see CLEAPSS Hazcard.
Sodium hydroxide pellets, NaOH(s), (CORROSIVE)- see CLEAPSS Hazcard.
Fluorescein - see CLEAPSS Hazcard.
Household bleach, which is typically a 5% 'available chlorine' solution, can be used. Make sure that the household bleach contains sodium chlorate(I) (sodium hypochlorite), NaOCl, and 1
not hydrogen peroxide, as the bleaching agent. Many household bleaches nowadays also contain thickeners and/or detergents. Use ‘economy’ bleaches without any additives.
The sodium chlorate(I) solution sold by chemical suppliers contains up to 14% available chlorine. It has a limited shelf life. Adjust the volumes of bleach and water to make up the diluted bleach solution for the demonstration. See 2
step Procedure . a
Tap water can be used for making up the solutions. The separate solutions are stable for over 12 hours and so can be made up well in advance. 3
The luminol does not always appear to dissolve completely, leaving a fine, greenish suspension. 4
Before the demonstration
Add 100 cm a
3 of the household bleach solution to 900 cm 3 of water in one of the flasks, mix well and stopper. Alternatively, add 50 cm 3 of commercial NaOCl solution to 950 cm 3 of water. See notes to 1 above. 3
In the other flask put 0.4 g of luminol, 1 dm b
3 of water and 4.0 g of sodium hydroxide. Swirl to dissolve the chemicals and then stopper the flask. See notes and 3 above. 4
Take the temperature of the solutions. c
Lower the room lights and slowly pour the two solutions at the same rate into the beaker so that they mix. A pale blue glow will be seen which will last for a few seconds. d
Take the temperature of the mixture. It will be the same as that of the starting solutions. e
For more dramatic effect, pour the solutions into a funnel attached to clear tubing bent into a variety of shapes, such as a spiral.
In the reaction, luminol is oxidised by the bleach to the aminophthalate ion, which is produced in an electronic excited state. This gives out energy as light (fluorescence) when it decays to the ground state.
Adding a small amount of fluorescein to the luminol solution, just before the demonstration, will alter the glow to a yellow-green colour.
Chemiluminescent ‘light sticks’ will be familiar to many students. A different reaction is used, involving the oxidation of a di-ester by hydrogen peroxide in an organic solvent. This reaction is much slower, the glow continuing for some hours. One solution is contained inside a vial inside a plastic tube containing the other solution. Bending the plastic tube breaks the vial, allowing the two reactants to mix. Colour effects are obtained by adding dyes to which the excitation energy is transferred, the excited dye molecules then emit light of different wavelengths. It is possible to slow the reaction down by placing the light stick in a freezer.
Health & Safety checked, July 2016
This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.
© Nuffield Foundation and the Royal Society of Chemistry
Page last updated July 2016