Objective: TO observe the fluorescent nature of tonic water, and how to quench it.
* Tonic water (must contain quinine)
Safety Precautions: Perform only under adult supervision. Do not start at the black light, as ultraviolet lights can be harmful to your eyes.
Completely darken the room and pour the tonic water into a cup under the black light.
Add salt to the tonic water, while it is still under the black light.
The tonic water contains quinine, which is highly fluorescent compound. Black light gives off ultraviolet light, which is invisible to the human eye. Quinine has the ability to absorb ultraviolet light from the black light and convert it to visible light. Substances that have this ability are termed fluorescent.
The tonic water is especially beautiful under the black light while it is being poured. When salt is added to the tonic water, it quenches the fluorescence. The chloride ion of the salt reacts with the quinine molecule, producing a product that is not longer fluorescent.