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OXIDATION-RESTORATION

 

Experience with sulfur dioxide showed us one of the many redox reactions. In such reactions the atoms of some substances attach electrons, and others give electrons. The first are called oxidizing agents (potassium permanganate), the second reducing agents (sulfur dioxide).

Will put some more experiments with oxidation - restoration.

Fresh cut potatoes add a drop of diluted iodine tincture: will appear blue in color. This starch found in potatoes, turns blue in the presence of free iodine. This reaction is often used to detect starch, it is also qualitative reaction.

On the same place where you have dripped iodine tincture, pour a little solution of sodium sulfite. The color will quickly disappear. Here's what happened: the sulfite gave free iodine electron, that has become electrically charged, turned into ion, and in this state, the iodine does not react with starch.

This property of sodium sulfite, and sulfur dioxide, means that these substances are good reducing agents. Here's another interesting experience with sulfite. His companion-oxidant again is potassium permanganate.

Four tubes pour pale pink, pink, light purple and dark purple solution of potassium permanganate. In each tube, add a solution of sodium sulfite. The contents of the first tube will be almost colorless, the second - brownish. In the third test tube will fall brown flakes in the fourth too, but sediment will be much more. All tubes are formed of solid manganese oxide MnO2. But in the first two tubes it exists in the form of a colloidal solution (solid particles are so small that the solution seems clear). And in the other two tubes, the concentration of MnO2 is so great that the particles stick together and fall out and the sediment.

In General, manganese resembles a chemical chameleon - so she is able to change its color. For example, in alkaline solution of permanganate of potassium from red-violet turns green, because the permanganate is restored to green manganate. To test this, throw in the alkali solution in concentrated boiled solution of washing soda - crystals of potassium permanganate, and instead of the usual pink coloring will appear green.

This experience is even more beautiful when working with caustic soda, but for home experimentation until you have the skill and abilities, such alkali recommend not. If you are involved in a mug, put the experience this way: pour in thin-walled glass little red solution of potassium permanganate (it should be transparent) and very small portions to the reaction mixture is warmed up, add enough concentrated solution of caustic soda. Watch the color of the liquid first, he will become more and more purple, and then, with increasing alkalinity, blue, and finally green.

The colors are particularly clearly visible in transmitted light. In any case, the lighting should be good, without the transitions of shades and not notice.

The following experiences will help you to distinguish dirty water from clean water. One tube will fill with clean water and the other water from stagnant pools or swamps. Add in tubes a little solution of the oxidizing agent is potassium permanganate. In tap water it will remain pink in the water from the puddles - will fade. In warm weather, in stagnant water accumulate organic matter. They, like sodium sulfite, restore potassium permanganate, change its color.

In the first experiment, sodium sulfite were asked to take it from a large Chuck of the developer. If you followed this advice, then you have a small cartridge that contains a mixture of metol and hydroquinone. Dissolve the mixture in water; the solution is very poorly painted. Add a bit of bleach (this is a common disinfectant substance should be managed carefully). The contents of the test tube will become yellow. Bleach is a good oxidant, it oxidizes hydroquinone to quinone, and he painted in yellow color. If you add in a test tube mixture of sodium sulfite and soda from a large cartridge, the yellow color will disappear: sodium sulfite again will restore the quinone to hydroquinone.

Recent experience on the topic of "oxidation - restoration", we will supply with chromium compounds. Such experiments are often colorful, which is not surprising, since "chromos" in Greek means "color".

So, take a little yellow solution of bichromate of potash (K2Cr2O7. This substance is widely used in engineering as an oxidant, for example, for cleaning heavily contaminated parts should be managed carefully. If you add in the slightly yellow solution of sulfuric acid (caution! pour the acid slowly!), it will turn red. In this acidified solution throw a few pieces of zinc. If you don't have granulated zinc, which is usually experiments, the extract zinc yourself from bad batteries: metal cups in the batteries - zinc.

So, you threw in a glass mortar with a little zinc, and bichromate, recovering, change the color to dark green. It was formed ions Cr3+. At the same time due to reaction of zinc with acid produces gas - hydrogen. If the reaction products are not oxidized by air oxygen, the reaction will go on, and will appear blue color - this color of solution of chromium sulfate CrS04. Pour it into another Cup; until you do, there will be oxidation, and the solution will again become green.

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

 

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Julia
2011-05-12 07:44:15
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