Glow in the Dark Ice

No (chemistry) party is complete without edible "glow in the dark" ice cubes.
To make your ice cubes:

•  open up some tonic water (or a bottle of "bitter lemon")
• pour it into an ice cube mold
• place the mold in the freezer until the tonic water solidifies (freezes)

To make your ice cubes glow in the dark:

• place some ice cubes in a glass of water (or cordial or carbonated beverage)
• place the glass under a UV ("black") light (even strong fluorescent light will work but the effect is not as dramatic!) and turn off the room's lights

Results : your glass of water and ice should glow a nice blue colour.


This is an example of fluorescence, the emission of light by a substance that has absorbed electromagnetic radiation. In the case of the tonic water, there is a compound in the tonic water that absorbs light in the ultraviolet region of the electromagnetic spectrum (wavelength ~ 350 nm), and emits light in the visible region of the electromagnetic spectrum (wavelength ~ 450 nm corresponding to bright blue or cyan).

The compound in the tonic water that fluoresces is known as quinine, with the molecular formula C₂₀H₂₄N₂O₂ and the structural formula shown below:

Quinine occurs naturally in the bark of the cinchona tree which is found in the tropical Andes forests of western South America. Quinine was the first effective treatment for malaria. The first medicinal uses involved drying the bark of the cinchona tree then grinding it into a powder which was then mixed into a drink (often wine), which was then drunk. The effective medicinal ingredient of the bark, quinine, was finally isolated in 1820 by French researchers Pierre  Joseph Pelletier and Joseph Bienaime Caventou.
During World War II, the Axis Powers had control over most of the commercial quinine production centres, so the Allied Powers were cut off from their supply of quinine, a necessary war-time commodity for fighting in the tropics. Then in 1944, the American chemists R.B. Woodward and W.E. Doering succeeded in producing quinine in the laboratory.




Quinine is no longer recommended as a first-line treatment of malaria, instead another plant-derived organic compound is used, artemisinin, but that's a different story.

Further Reading:
Emission Spectroscopy
Empirical Formula
Relative Molecular Mass (molecular weight, formula mass, formula weight)
Percent Composition
Parts per Million Concentration
Functional Groups


Suggested Study Questions:

1. Draw a diagram to describe what happens when quinine absorbs UV light and emits bright blue/cyan light.
2. Imagine you were to view the light emitted by the tonic water through a spectroscope. Draw a sketch of the emission spectrum you would expect to see.
3. Use the molecular formula for quinine to find its empirical formula.
4. Calculate the relative molecular mass (molecular weight, formula mass, formula weight) of quinine.
5. Calculate the percentage of each element present in quinine.
6. Assume a 1L bottle of tonic water contains 15ppm quinine. Calculate the
   • mass of quinine contained in the bottle
   • moles of quinine in the bottle
   • quinine concentration in mol L^-1
7. Using the structural formula for quinine, identify an aliphatic double bond (that is, a double bond that does not occur in an aromatic ring), an aromatic (benzene) ring, and an hydroxyl group