Chemistry Experiments You Can Do at Home


How can I make Jell-O® that glows under a black light?

  • Fluorescence
  • Gels
  • Cross-linking
  • Jell-O® or gelatin powder
  • 1 cup of tonic water
  • 1 cup of water
  • Stovetop or microwave
  • Large bowl
  • Pot (for heating on stovetop)
  • A black light source (see “Physical and Theoretical Chemistry” to review how black lights work)
  1. Heat one cup of water to a boil.
  2. Mix the Jell-O® and the hot water into the bowl, and stir the powder in until it dissolves. The hot water helps the gelatin to dissolve and disperse evenly throughout the solution. Gelatin is a form of collagen (See “Chemistry in the Kitchen”), and when it cools, the Jell-O® will reform cross-links between the collagen strands, which is what traps the water inside to create a gel. You’ll recall that a gel is solid material that consists of a bonded network of long strand molecules that contain significant amounts of molecules that would otherwise behave as a liquid trapped within the solid network.
  3. Add in one cup of tonic water, stir the solution well, and then place it in the refrigerator for about four hours. The tonic water contains a molecule called quinine that will fluoresce a bright blue color when excited with the appropriate wavelengths of light, which can be provided by the black light. Recall that fluorescence takes place when a molecule absorbs light at one wavelength, relaxes to release a fraction of that energy, and then emits a photon at a longer wavelength (lower energy) than that which was absorbed. Black lights provide light that is at slightly shorter wavelengths (higher energies) than light in the visible spectrum, so it can often excite molecules that will fluoresce in the visible region of the spectrum.
  4. When the Jell-O® is finished hardening, take a look at it under the black light. It should glow blue! This is due to the fluorescence of the quinine from the tonic water. This blue glowing color comes from the fluorescence of the quinine molecules, so it will not be affected significantly by the flavor or color of Jell-O® that you decided to use.


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