Oxidation-reduction. Fun chemistry experience at home

ENTERTAINING EXPERIENCES AT HOME
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Oxidation-reduction. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

Let's put some experiments with oxidation - reduction.

On a fresh slice of potato, drip dilute iodine tincture: a blue color will appear. It is the starch found in potatoes that turns blue in the presence of free iodine. Such a reaction is often used to detect starch, which means that this is also a qualitative reaction.

In the same place where you dropped the iodine tincture, pour a little sodium sulfite solution. The color will fade quickly. This is what happened: sulfite gave an electron to free iodine, it became electrically charged, turned into an ion, and in this state, iodine no longer reacts with starch.

This property of sodium sulfite, like sulfur dioxide, means that these substances are good reducing agents. Here is another interesting experience with sulfite. Its oxidizing companion will again be potassium permanganate.

Pour pale pink, pink, light purple and dark purple solutions of potassium permanganate into four test tubes. Add sodium sulfite solution to each tube. The contents of the first tube will become almost colorless, the second - brownish. In the third tube, brown flakes will fall out, in the fourth, too, but the sediment will be much larger. Solid manganese oxide MnO is formed in all test tubes₂. But in the first two test tubes, it exists as a colloidal solution (the solid particles are so small that the solution appears clear). And in the remaining two test tubes, the concentration of MnO₂ so large that the particles stick together and precipitate.

In general, potassium permanganate resembles a chemical chameleon - this is how it can change its color. For example, in an alkaline environment, a solution of potassium permanganate turns from red-violet to green because the permanganate is reduced to green manganate. To check this, drop a potassium permanganate crystal into an alkali solution - into a concentrated boiled solution of washing soda, and green will appear instead of the usual pink color.

This experience is even more beautiful when working with caustic soda, but for home experimentation, until you have the skill and ability, such alkalis cannot be recommended. If you are studying in a circle, then set up the experiment like this: pour a little red solution of potassium permanganate into a thin-walled glass (it should be transparent) and in very small portions so that the reaction mixture does not warm up, add a sufficiently concentrated solution of caustic soda. Watch the color of the liquid - first it will become more and more purple, then, as the alkalinity increases, blue, and finally green.

The color change is especially clearly visible in transmitted light. In any case, the lighting should be good, without this, the transitions of shades may not be noticed.

The following experiment will help you distinguish dirty water from clean water. Fill one test tube with clean water, the other with water from a stagnant puddle or from a swamp. Add a little solution of the oxidizing agent - potassium permanganate to the test tubes. In tap water, it will remain pink; in puddle water, it will become discolored. In warm weather, organic matter accumulates in stagnant water. They, like sodium sulfite, restore potassium permanganate, change its color.

In the first experiment with sodium sulfite, it was proposed to take it from a large developer cartridge. If you followed this advice, then you are left with a small cartridge that contains a mixture of metol and hydroquinone. Dissolve this mixture in water; the solution will be very faintly colored. Add some bleach (it's a common disinfectant and should be handled with care). The contents of the tube will turn yellow. Chlorine is a good oxidizing agent, it oxidizes hydroquinone to quinone, which is colored yellow. If, however, a mixture of sodium sulfite and soda is now added to the test tube from a large cartridge, the yellow color will disappear: sodium sulfite will again reduce quinone to hydroquinone.

The last experiment on the topic "oxidation - reduction" we will deliver with chromium compounds. Such experiments are often colorful, which is not surprising, since "lame" in Greek means "color".

So, take some yellow potassium bichromate solution K₂Cr₂О₇; this substance is widely used in engineering as an oxidizing agent, for example, for cleaning heavily contaminated parts; it must be handled with care. If you add a little sulfuric acid to the yellow solution (carefully! pour the acid slowly!), then it will turn red. Throw a few pieces of zinc into such an acidified solution. If you do not have granular zinc, which is usually used for experiments, then extract zinc yourself from an unusable battery: metal cups in batteries are zinc.

So, you threw a little zinc into a glass with a solution, and the bichromate, recovering, changes color to dark green. It formed Cr ions³⁺. At the same time, due to the reaction of zinc with acid, gas is released - hydrogen. If the reaction products are not oxidized by atmospheric oxygen, then the reaction will continue, and a blue color will appear - this is the color of a solution of chromium sulfate CrSO₄. Pour it into another glass; while you do this, oxidation will occur and the solution will turn green again.

Author: Olgin O.M.

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