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During some chemical reactions of the energy is released in the form of light. Such a process is called by chemiluminescence. Sometimes chemiluminescence occurs in living organisms: the most obvious example of a well - known fireflies. A faint glow appears and the oxidation of some organic compounds. You can watch it in experience with the oxidation of hydroquinone. The final stage of this experience must be conducted in the dark to the light was noticeably better.

Dissolve 1 g of hydroquinone and 5 g of potassium carbonate (potash) in 40 ml of pharmacy formalin is an aqueous solution of formaldehyde. Pour the reaction mixture into a large flask or bottle with a capacity of not less than one litre.

In a small vessel, prepare 15 ml of concentrated peroxide solution (hydrogen peroxide) hydrogen. You can use the tablets hydropenia - compounds of hydrogen peroxide with urea (the second component of the experience does not hurt). Put both vessels in a dark room so that they were at hand. As soon as your eyes adjust to the dark, add peroxide solution in a large vessel. At once the mixture starts to foam (because of this, we ask you to take the vessel more) and you will see a distinct orange glow.

The chemical energy released during the oxidation of hydroquinone peroxide in an alkaline medium, almost completely transformed into light, not heat, as usual. However, the heat of reaction is also released, so little formaldehyde evaporates. And because he stinks, then, first of all, do not lean over the vessel and, secondly, immediately after the experience ventilate the room.

Glow may appear not only in the oxidation. Sometimes it occurs during crystallization. This phenomenon has long been known; you can see it.

The easiest object of observation - salt. Dissolve it in water and take salt so much that at the bottom of the glass remained any insoluble crystals. Received a saturated solution pour in another Cup and dropwise using a pipette, carefully add to this a solution of concentrated hydrochloric acid. Salt begins to crystallize and this would create a glow - in solution will be to slip a little spark. To see them, experience also should be put in the dark.

Behave in a similar way during crystallization and some other salts - potassium chloride, barium chlorate. In all cases, the sparks appear only when you add salt (chloroethanol) acid. But perhaps the most eye-catching experience with a mixture of the sulphates of potassium and sodium. Mix 200 g of potassium and 80 g of sodium salt and small amounts add hot water to them. When all the crystals dissolve, leave the solution to cool. The room in which you put the experience should be darkened. First, very weak spark will appear at 60°C. Then they will become more and more. When the crystals will fall out a lot, you will see a fountain of sparks, but this has to wait a long time - sometimes for an hour. If you put your ear to the vessel wall, you can hear something like a thunder. Glow in this case, due probably to the formation of double salts 2K2SO4*Na2SO4 *10h2O.

The solution with crystals do not pour the experiment can be repeated and after the glow stops. Slide glass stick on crystals that are under the liquid, or just shake a few times a vessel with crystals - sparks will appear again.

Here's another experience with glow during crystallization (this phenomenon is called crystallochemistry). It will have to prepare bromate barium BA(Ged3)2 of more affordable substances potassium bromate, Kugo3 and barium chloride ВаСl2. Since the solubility of the first of them small, have to take a diluted solution of about 3%concentration. If the mixture of reagents to cool, the precipitate will fall out of the desired salt in cold water bromate barium is almost insoluble.

Filter, wash with cold water and dry bromate barium, then deal 2 g, dissolve in 50 ml of boiling water, and again filter the solution. A glass mortar place to cool off, but not at room temperature, and at a slightly higher - 40-45°C (preferably in a drying Cabinet). At this temperature the solution will appear blue sparks and heard clapping again MicroProse in the beaker...

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986


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