Mentos and Tonic Water Glow in the Dark Fountain

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Mentos and Tonic Water Glow in the Dark Fountain

The Mentos and tonic water glow in the dark fountain is a fluorescent take on the classic Diet Coke and Mentos project. Basically, all you do is drop the candies into a bottle of tonic water, producing a shower of blue glowing liquid thanks to the quinine in the beverage. While tonic water actually fluoresces visibly in sunlight, the glow is much brighter under a black light, which emits ultraviolet light.

Materials

You only need a few basic materials for this project:

  • Tonic water
  • Mentos candies
  • Black light

Either regular or diet tonic water works, but the diet version is not sticky so clean-up is easier. Be sure the tonic water contains quinine. If the label does not list it as an ingredient, then the project won’t glow under the black light.

The mint flavor of Mentos candies works best, but any flavor is fine. If you can’t find the candy, salt or sand works instead. Some other candies are fine.

Ideally, use a 2-liter bottle of tonic water. This gives the biggest fountain effect. That being said, the 1-liter and 20-ounce bottles are fine. Just make sure the candy fits through the bottle neck.

Make a Mentos and Tonic Water Fountain

It’s simple!

  1. Turn on the black light. Admire the brilliant blue glow of the tonic water.
  2. Open the bottle.
  3. Drop in all of the candies at once. An easy way of stacking and dispensing the candies is rolling then inside of a paper or cardboard tube.
  4. Were you quick enough to step away before getting drenched with glowing liquid?

How the Mentos and Tonic Water Glow in the Dark Fountain Works

The glowing part of the project is from the fluorescence of quinine. While most chemicals that absorb ultraviolet light release the energy as heat, quinine releases it as blue light.

The fountain effect comes from the rapid de-gassing of carbon dioxide in the tonic water, just as in the normal Diet Coke and Mentos project. The candies displace liquid as they fall. Their coating dissolves, releasing gelatin and gum arabic into the liquid. These chemicals lower the liquid’s surface tension and make the fountain more foamy and bubbly than if you just shook up the carbonated bottle and opened it. Tiny bits on the candy surface act as nucleation site for dissolved carbon dioxide to form carbon dioxide gas bubbles. The de-gassing happens rapidly, shooting the soda into the air.

Tips and Further Exploration

  • Room temperature or warm tonic water works better than chilled soda.
  • If you can’t find tonic water with quinine (or just want to try more things), add laundry detergent with whitening agents to any colorless carbonated beverage. Some types of powdered lemonade are also fluorescent. Certain vitamins, oils, and other foods also fluoresce or glow under black light. Highlighter pen ink often glows in different colors, too.
  • Adding a capful of chlorine bleach to the tonic water quenches the glow. Consider trying other oxidizing agents, too, like OxiClean (sodium percarbonate) or hydrogen peroxide. Oxidizing agents break the carbon-carbon double bonds in the quinine so that it can’t absorb ultraviolet light. If it does not absorb energy, it doesn’t emit blue light.

References