Redox reactions

In redox reactions, atoms of some substances attach electrons, while others give electrons. The first ones are called oxidizers, the second ones are reducing agents. We will show several experiments of redox reactions.

In redox reactions, atoms of some substances attach electrons, while others give electrons. The first ones are called oxidizers, the second ones are reducing agents

For a fresh potato slice, drip with diluted iodine tincture: a blue color will appear. This starch contained in potatoes turns blue in the presence of free iodine. This reaction is often used to detect starch. Then, in the same place where you dripped iodine tincture, pour a little solution of sodium sulfite. Coloring will quickly disappear. What happened is this: 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 means that this substance is a good reducing agent. Here is another experience with potassium permanganate sulfite and oxidant.

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

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

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

The latest experience on the topic of redox reactions will be put with chromium compounds. Such experiences are often colorful, which is not surprising, since "lame" in Greek means "color".

So, take a little yellow solution of potassium bichromate K2Cr2O7; this substance is widely used in the technique as an oxidizing agent, for example, for cleaning highly contaminated parts; Handle it carefully. If you add some sulfuric acid to the yellow solution (carefully pour the acid slowly!), It will turn red. In this acidified solution, throw a few pieces of zinc. After this bichromate, recovering, changes color to dark green. This formed ions r3+. At the same time due to the reaction of zinc with acid gas is released - hydrogen. If the reaction products are not oxidized by oxygen in the air, the reaction will continue, and a blue color will appear - this is the color of the chromium sulfate CrSO4 solution. Pour it into another glass; while you do this, oxidation will occur, and the solution will turn green again.