You will need
- - a piece of thin copper wire;
- - "taped";
- - source flame, such as a spirit lamp or gas burner.
Some people have seen the bronze monuments that are literally painted in light green color. This is not the work of vandals, as it may seem at first glance - it was the reaction of oxidation. Recall that bronze is an alloy of copper and tin. A monument under the open sky, exposed to rain. While in the air is a fair amount of oxygen and carbon dioxide. Here a chemical reaction takes place:2Cu + H2O + CO2 + O2 = Cu2CO3(OH)2.Formed the green stuff is malachite! The one sung by the storyteller Bazhov. Him old bronze monuments owe their color.
It is easy to guess that the wetter the climate the more industrial and automotive exhaust, the faster you will oxidize the copper contained in bronze. You can also do a very simple and visual experience for the oxidation of copper.
Firmly clamp the wire "taped" (a wooden clothespin or a pair of pliers) and make the free end in the flame of a spirit lamp or burner. Keep them so for some time to the wire is well punctured. After that, remove from fire. You'll clearly see that the cooled wire changed color, it became black. It happened the oxidation reaction, which is as follows:2Си + O2 = 2CuO.
You can continue the experience by placing the black end of the wire into a test tube with dilute hydrochloric acid. Your eyes wire again will be the color inherent in pure copper, and the acid solution will be light blue, because that was the recovery of copper oxide with the formation of its soluble chloride. The chemical reaction in this case would be:CuO + 2HCl = CuCl2 + H2O.
Remember that it is necessary to observe safety measures when working with an open flame and caustic substance (hydrochloric acid).