School of Mathematics and Natural Sciences

Color through Emission of Light

Chemicals

GHS Pictograms

Tartaric Acid - DANGER

H318
P280, P305+P351+P338

Esculin

Not a dangerous substance according to GHS.

A big test tube is filled with about 5g of tartaric acid. The test tube is fiated in a clamp that is held in one hand. The tartaric acid is carefully heated above the non-glowing flame of a gas burner until it is melted. The test tube is removed from the heat as soon as a clear molten substance is reached. Now about 5 mg of esculin are added (see picture on the right to roughly estimate the amount).

The molten tartric acid is carefully shaken to solve the esculin, and the mixture is then distributed in a large area on the inside of the test tube by tilting it and turning it around. After this step the test tube is set to cool to room temperature.

  • When the sample is irradiated in the dark with violet light from an LED flashlight, it glows in a bluish-white color. Immediately after switching off the light source, the sample glows in a greenish-yellow color; the glow fades in 1s to 3s.
  • A sample cooled to approx. 0 °C in an ice-water bath will glow longer than the sample at room temperature.
  • A sample heated to approx. 60 °C in the burner flame or in a water bath (do not heat until it melts) glows blue in the violet light of the LED flashlight; no subsequent glow can be observed when the lamp is switched off.

The following additional experiments are recommended:

  1. A sample from 5 g tartaric acid and approx. 2 mg fluoresceine is prepared and investigated as described above. The sample's glow as well as its subsequent glow is more intensive compared to the sample made from esculin, but a difference in color between the glow and the subsequent glow can't be determined. The duration between glow and subsequent glow depends also on temperature as it does with the sample made with esculin.
  2. Conducting the Experiment „Crying Chestnut Branch
  3. Observation of bank notes, credit cards, identity cards and glowing objects from craft and toy shops in the light of LED flashlights (λ = 365 nm and λ = 400 nm). During this the differences in color between day light and in the light of these flashlights should be noted and it should be investigated whether a subsequent glow occurs and what color it has.
  4. Experiments with water-soluble and water-insoluble fluorescent colours from highlighters as well as chlorophylls and carotenoids from leaves, flowers and fruits..
    cf. experimental kit Photo-Mol and the workshop light laboratory: leaf

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