Thames & Kosmos Glowing Chemistry handleiding

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Thames & Kosmos

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In that reaction, the luminol undergoes conversion with

oxygen — a process resembling combustion. When materials

undergo combustion, the energy that is released in that

process is given off as heat. With luminol, on the other hand,

the energy is given off as light.

The oxygen for the reaction comes from the hydrogen

peroxide, and the sodium carbonate ensures that the solution

is basic (the opposite of acidic), without which the substances

wouldn’t react.

The light solution composed of luminol, sodium carbonate,

and hydrogen peroxide nevertheless remains dark, as you saw

in Experiment 17. It’s not all that easy for the hydrogen

peroxide to break down. For the light-emitting reaction to

occur, you need an additive, or a so-called

catalyst

. This is the

role played by the potassium hexacyanoferrate(III), for

example. In Experiment 19, the

traces of blood

play that role,

as do the

radishes

(which contain hydrogen peroxide-

decomposing

peroxidases

) in Experiment 20. Proteins like

these can be found in many living things, including humans.

They always have the task of decomposing hydrogen

peroxide, which accumulates in the cells as a harmful by-

product and thus must constantly be eliminated.

What happens

during the light-emitting

chemical reaction?

The discovery of phosphorus

The chemical element phosphorus was discovered with the help of the

light that it emits when exposed to air. Over 300 years ago, the German

alchemist Henning Brand attempted to make a “philosopher’s stone”

(which was supposed to grant eternal life and wealth) out of urine. To do

that, he heated a large quantity of urine for a long while until all the

water evaporated, and then heated what remained in an enclosed glass

flask. When he opened the cooled flask, it suddenly emitted bright light.

Brand called the light-generating substance phosphorus, after the Greek

word phosphoros, meaning light-bearer. This discovery was a great

sensation at the time. Today we know that the process of heating urine

converted naturally-occurring phosphorus compounds into so-called white

phosphorous, which emits light when it comes into contact with oxygen in the air — a typical

case of chemiluminescence.

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