Electrolysis is a non-spontaneous reaction caused by the supply of electricity from a generator (batteries). It is the inverse of the batteries.
Electrolysis has many applications in the chemical industry, in the production of metals such as sodium, magnesium, potassium, aluminum, etc. Also in the production of nonmetals, such as chlorine, fluorine and even substances such as sodium hydroxide (caustic soda) and hydrogen peroxide (hydrogen peroxide), and the deposition of thin metal films on metal or plastic parts.
This metal deposition technique is known as galvanization. The most common are chrome deposition (chrome plating), nickel (nickel plating), silver (silverware) and gold (gilding) used in grilles, car covers, badges, refrigerator parts, jewelry and stereos.
It is also used in the purification or electrolytic refining of many metals, such as copper and lead. And in anodizing process, it is nothing more than a forced oxidation of the surface of a metal to be more corrosion resistant. Anodizing is done on aluminum.
In electrolysis, inert (non-governing) electrodes such as carbon graphite or platinum are used. For electrolysis to occur there must be:
- continuous electric current and sufficient voltage to cause electrolysis;
- free ions (by fusion or dissolution)
There is igneous electrolysis and aqueous electrolysis.
It is an electrolysis where there is no water present. Ionic metals are molten (molten). When they merge, they ionize, forming ions. From these ions, the electric current is formed.
Melting reaction (solid to liquid physical state transformation) of NaCl at 808 ° C:
The electrodes must be inert. It can be graphite carbon or platinum.
These electrodes are polarized, one negatively charged and one positively charged, and placed in a cuvette with the molten NaCl metal.
Note that in the drawing there are two electrically charged electrodes, the positive pole and the negative pole, dipped in a molten metal.
The above reaction shows the formation of Na + and Cl- ions. When these ions come into contact with the electrodes, the positive ions (Na +) will go to the negative electrode. The negative ion (Cl-) will go to the positive electrode.
On the negative electrode, metallic sodium (Na °) will be formed. On the positive electrode, chlorine gas (Cl2). Note the formation of bubbles.
The positive electrode is called the anode and there occurs the oxidation reaction.
The negative electrode is called the cathode and the reduction reaction occurs in it.
The cathode reaction must be multiplied by 2 to be able to cancel with the anode reaction as it forms chlorine gas (Cl2).