Chameleon in a Test Tube
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The following article was originally published in the journal for educators Biologia w Szkole (eng. Biology in School) (5/2022):
It may come from a test tube or another laboratory vessel—it all depends on our resources and imagination. However, before we conduct the experiment, let us first get acquainted with the animals that lent their name to this experiment.
Chameleons Chamaeleonidae, belonging to the order of scaled reptiles Squamata, are a family of reptiles renowned for their ability to change color, their hunting method using a long tongue, and their unique body shapes. Their name comes from the Greek χαμαιλέων (khamailéōn), a compound of χαμαί (khamaí), meaning “on the ground,” and λέων (léōn), meaning “lion”—so essentially, “chameleon” means “ground lion,” likely alluding to the creature’s combative behavior in times of danger.
Chameleons are, for the most part, creatures highly specialized for an arboreal lifestyle. Their bodies are noticeably laterally flattened—particularly evident along the back, where the skin forms a flat ridge with a sharp edge. Their limbs are relatively slender and of equal length. The digits—on both the front and hind limbs—are fused together, forming pseudo-pincers. An extra limb is provided by their long, prehensile tail. The lizard’s head is angular, often vaulted, and sometimes adorned with horn-like protrusions [1].
The eyes of chameleons are truly astounding. They move independently, allowing each eye to gaze in a different direction. Their eyelids, however, are fused together, leaving only a small pupil opening. As a result, chameleons enjoy an enormous field of view, and this visual system also enables stereoscopic vision when both eyes focus on the same object. Their prehensile tongue is exceptionally long, broad at the tip, and coated in sticky mucus, which helps them catch insects.
Chameleons are popular in home terrariums and zoos. One of the more commonly encountered species is the Yemeni chameleon Chamaeleo calyptratus—one of the largest lizards in the entire family (Photo 1).
Chameleons are well known for their remarkable ability to change color. However, it should be noted that, contrary to popular belief, these reptiles do not simply match their coloration to their surroundings. In reality, their hues shift in response to changes in their physical condition and emotional state—and this is likely also a form of communication with other individuals. That said, chameleons do employ a measure of camouflage, as their colors are often similar to those of their environment.
In our lab, we can conduct an experiment named after this fascinating creature—a chemical chameleon in the form of a solution that changes color [2].
Experiment
We must gather the following substances:
- Potassium permanganate (KMnO4),
- Sodium hydroxide (NaOH),
- Glucose (C6H12O6).
In this experiment, we use NaOH, a strong base with potent corrosive properties. Potassium permanganate is hazardous and can severely stain fabrics and skin. It is essential to use proper personal protective equipment.
Potassium permanganate is often marketed under this very name and finds wide application in industry, chemical synthesis, and analysis. It is also employed in medicine as a disinfectant [3] [4]. It can be easily purchased at pharmacies—and because of its distinctive color, it is sometimes called “violet” (a nickname that is also applied to other substances). Under normal conditions, this compound appears as dark violet crystals (Photo 2).
Potassium permanganate readily dissolves in water, where it acts as an antiseptic (Photo 3).
Glucose is an organic compound—a simple sugar classified as an aldohexose. It is a white, fine-crystalline solid (Photo 4) that readily crystallizes from aqueous solutions as a monohydrate. The taste of its water solutions is sweet, though somewhat less so than that of sucrose.
Glucose serves as the primary energy molecule for most organisms, stored in the form of its polymers—chiefly starch and glycogen. It is the sugar most easily metabolized by humans. In the food industry, it is often referred to as “grape sugar.”
Sodium hydroxide can be used in its pure chemical form or as a drain cleaner (but be sure to check its composition first).
Once we have gathered the necessary substances, we can proceed with the experiment.
First, we need to prepare the solution. In 20 cm3 (0.7 fl oz) of distilled water, we dissolve approximately 0.3 g (0.01 oz) of NaOH along with a few small crystals of potassium permanganate. The resulting solution exhibits a violet-pink hue (Photo 5).
Separately, we prepare a solution of a small amount of glucose in water. Upon mixing the two solutions, we observe a gradual change in color. The hue shifts progressively from violet (see Photo 5), to blue, then green, and finally the liquid takes on a yellowish tint (Photo 6).
As you can see, this solution really does change color as effortlessly as a chameleon!
Explanation
Glucose is a reducing sugar, as demonstrated by the outcome of Fehling’s test [5].
Manganese in the +7 oxidation state gives the solution a beautiful, characteristic violet-pink color typical of permanganates. In a basic environment, glucose reduces the manganese from the +7 to the +6 oxidation state, at which point the solution turns green. The blue color is an intermediate stage and is not associated with any characteristic ions. The manganese is then further reduced to the +4 oxidation state [6], forming an insoluble precipitate of MnO2 that, when suspended in the solution, imparts a straw-yellow color. This compound occurs in nature as the mineral braunite, one of the most important manganese ores.
References:
- [1] Glaw F., Taxonomic checklist of chameleons (Squamata: Chamaeleonidae), Vertebrate Zoology, 2015, 65 (2), pp. 167–246 back
- [2] Arora C.L., Lecture demonstration of the various oxidation states of manganese, Journal of Chemical Education, 1977, 54(5), pp. 302-303 back
- [3] Bielański A., Chemia ogólna i nieorganiczna, PWN, Warszawa, 1981, pp. 582 back
- [4] Kemmitt R.D.W., Peacock R.D., The Chemistry of Manganese, Technetium and Rhenium, Pergamon Press, 1973, pp. 771-798, 811-813, 851, 859 back
- [5] Ples M., Kto pomieszał cukry? Mała analiza (eng. Who Mixed the Sugars? A Brief Analysis), Biologia w Szkole (eng. Biology in School), 1 (2018), Forum Media Polska Sp. z o.o., pp. 58 - 63 back
- [6] Lee D.G., Chen T., Mechanism of the reaction between permanganate and carbon-carbon double bonds, Journal of the American Chemical Society, 1989, 111(19), pp. 7534–7538 back
All photographs and illustrations were created by the author.
Addendum
As a supplement to the above article, I would like to present the Reader with a short video:
Marek Ples