Experiments with magnesium

Many of the surrounding metal objects can be corroded. And this does not surprise anyone, because oxygen and water interact quite intensively with many metals. But, for example, some do it quickly and with the release of heat - practically explode - sodium, potassium, lithium. Others, such as iron, are oxidized for a long time. And there are also metals that seem to be active, but for some reason react with other substances more slowly. Magnesium also belongs to them. Let's look at interesting experiments with magnesium and try to figure out why this is possible.

Magnesium also belongs to them. Let's look at interesting experiments with magnesium and try to figure out why this is possible

Magnesium can already decompose water at room temperature according to the reaction:

2Mg + 2H2O = 2Mg(OH)2 + H2.

In this reaction, we observe the formation of magnesium hydroxide, which is very poorly soluble in water. It remains on the surface of the metal in the form of a thin film, which protects the metal from further dissolution. Such or similar protective mechanism is characteristic for many active metals, for example, for aluminum.

But let's try the next experiments with magnesium. Take a little magnesium powder and place in a flask of water. Next, we will heat the flask on the spirit lamp, after adding a few drops of an alcohol solution of phenolphthalein. As a result of heating, the liquid will turn red. This means that already a small amount of magnesium hydroxide (less than 0,1 mg/l) leads to the fact that the indicator shows the main reaction. The experience shows that many chemical reactions have a greater sensitivity.

But in the above reaction, in addition to magnesium hydroxide, we also have hydrogen, resulting from the decomposition of water by magnesium. Since in pure water the reaction ceases quickly due to the formation of a protective film of hydroxide, it is necessary to change experiments with magnesium so that this protective layer is destroyed. For this, additives are needed in the water - a small amount of acid or salts. Such salts include, for example, trivalent iron chloride or magnesium chloride. To conduct experiments with magnesium, place a little magnesium powder in several wide tubes. In one of the tubes we will pour water, in the other - water with a small amount of acid, for example, vinegar, in the third - water with dissolved in it salt of ferric chloride or table salt. We will observe how in the test tubes, where water is acidified or there are solutions of salts, gas bubbles are formed, and magnesium dissolves vigorously. If you fill a narrow test tube with water and, turning it over, immerse it in a wide tube, you can collect the gas that is released during the reaction. Especially a lot of it is formed in a test tube with acidified water. If hydrogen generated during the reaction is ignited, it burns quietly with a blue flame to form water. However, if hydrogen forms a mixture with air or oxygen, which is also called an explosive gas, combustion will be accompanied by cotton. Therefore, by conducting experiments with the formation of hydrogen and making a test for its presence with the help of fire, just in case, wrap the tube with a damp cloth, so as not to get injured in case of a possible explosion.

Such experiments with magnesium, as with other active metals, show the presence on their surface of a protective passivating film that protects the metal from corrosion. If it were not for this film, then products made of metals such as magnesium, chromium, aluminum and many others would be destroyed in a short time from the action of oxygen of air or water vapor.

Tools