With copper you can put some interesting experiences, so dedicate a special page.
From a piece of copper wire, make a small spiral and tie it to a wooden taped (you can leave the free end of sufficient length and wind it on a regular pencil). Flame the bacteriological spiral in the flame. Its surface is covered with a black coating of copper oxide CuO. If blackened wire dipped in diluted hydrochloric acid, the liquid will turn blue and the metal surface will again become red and shiny. Acid, if it is not heated, no effect on copper, but it dissolves the oxide, transforming it into a salt CuCl2.
But here's the question: if the copper oxide black, why antique copper and bronze items not covered in black and green tinge, and what is plaque?
Try to find the old copper object, say, a candlestick. Scrape off with a bit of green plaque and place in a test tube. The neck of the tube, close the tube with a draining pipe, the lower end of which in lime water (how to cook, you already know). Heat the contents of the test tube. On its walls will gather drops of water, and the gas discharge tube will be emitted gas bubbles, from which lime water becomes cloudy. Therefore, this carbon dioxide. In vitro will remain black powder, which, when dissolved in acid gives a blue solution. This powder, as you can probably guess,the copper oxide.
So, we learned which components decomposes green plaque. Its formula is written as: CuCO3*cu(OH)2 (basic copper carbonate). It is formed on the copper objects, because the air always has and carbon dioxide, and water vapor. Green plaque is called patina. The same salt found in nature - it is nothing like the famous mineral malachite.
Let us again turn our attention to the blackened copper wire. Is it possible to restore its original luster without the aid of acid?
Pour into a test tube pharmacy ammonia were heated red-hot copper wire and dip it in the bubble. The spiral and the hissing and will again become red and shiny. In an instant reaction occurs, which produces copper, water and nitrogen. If the experiment is repeated several times, then ammonia in a test tube will turn blue. Simultaneously with this reaction proceeds and other so-called reaction of complex formation is formed the same complex compound of copper, which previously allowed us to accurately determine the ammonia on the blue coloration of the reaction mixture.
Among other things, the ability of copper to react with ammonia use for a very long time (since the days when the science of chemistry was not in sight). Solution of ammonia, i.e., liquid ammonia, was purified to Shine copper and brass items. So, by the way, experienced mistress come now; for greater effect ammonia mixed with chalk, which is mechanically attire dirt and adsorbs impurities from the solution.
The following experiment. Pour into a test tube with a bit of ammonia-ammonium chloride, NH4Cl, which is used when soldering (do not confuse it with ammonia NH4OH , which is an aqueous solution of ammonia). Hot copper coil tap substance layer covering the bottom of the tube. Again you hear the hiss, and will be soaring up the white smoke particles evaporate ammonia. And the spiral again will Shine pristine copper glitter. Have a reaction, in which was formed the same products as in the past, and in addition the chloride copper СuСl2.
It is because of this ability to recover metallic copper oxide - ammonia and is used when soldering. The soldering iron is usually made of copper, which is a good conductor of heat; when his "stinger" is oxidized, copper loses the ability to retain on their surface tin solder. A little ammonia and nitric oxide as usual.
And last experience with a copper spiral. Pour into a test tube with a little eau de Cologne (even better - pure alcohol) and again make a hot copper wire. The result of the experience you are likely already present: the wire was again cleared of oxide film. This time happened complex organic reaction: copper recovered, and ethyl alcohol contained in Cologne, were oxidized to acetaldehyde. This reaction in everyday life is not used, but sometimes it is used in the laboratory, when alcohol is necessary to obtain the aldehyde.