Methods of copper oxidation
How it reacts with air
Copper oxidation is a natural process. Copper is an element that belongs to the group of metals and holds 29th place on Mendeleev’s periodic table. Copper, like all other metals, is capable of oxidation, forming stable bonds in the forms of oxides and salts. To understand what copper oxide is, you can look at an old bronze statue which has been standing for many years. The statue will be of a light green color, because the copper contained in bronze has oxidized. A new bronze statue will be the color of brick, but from moist air and carbon dioxide, over time the following reaction takes place:
2Cu + H₂O + CO₂ + O₂ → CuCO₃•Cu(OH)₂
This combination of copper salt and hydroxide is called malachite, which is used to make paints and jewelry:
There are many methods of oxidizing copper items. In industry, oxidized copper is made by anodic oxidation, using electrodes. This method, which requires special equipment, is a complex and expensive process. Oxidation at home is much more straightforward.
Copper oxidation at home
To understand fully what copper oxidation is, we can conduct an experiment. It’s not difficult to make copper oxide at home. We will need the following:
- copper wire;
- gas or spirit burner;
- solution of hydrochloric acid;
- solution of ethyl alcohol;
- ammonium chloride;
- earthenware plate.
So, holding the copper wire with the pliers on one side, we put the free end of the wire into the flame of the burner and heat it. Thanks to the high burning temperature, over time the wire turns black. In the chemical reaction process, copper transforms into copper oxide:
2Cu + O₂ = 2CuO
Then we put the copper wire in a hydrochloric acid solution. We immediately see that the solution changes from colorless to turquoise. This color is characteristic for copper chloride, which is formed in the reaction process:
CuО + 2HCl = CuCl₂ + H₂О
Note that the copper wire has once more turned a light brick color.
The black copper wire is also reduced using ethyl alcohol. Put it into a flask of ethyl alcohol, and the copper item will once more turn a golden color. Thus, as a result of a complex chemical reaction, ethyl alcohol oxidizes to acetic aldehyde. Click here, for doing amazing experiments with copper.
To turn the darkened copper wire back to its original color, we can also use a powder in the form of ammonium chloride.
We need to create the following chemical interaction:
CuО + 2NH₄Cl = 2NH₃ + H₂О + CuCl₂
We put the hot copper wire on the bottom of an earthenware bowl containing ammonium chloride (NH₄Cl). As a result of the reaction, ammonia gas will be released, and the darkened copper wire will once more turn gold.
During chemical experiments, you should follow safety rules when working with a gas or spirit burner, and also with aggressive substances such as hydrochloric acid.