Electrolysis is the physicochemical process in which an electric current is converted into chemical energy with the formation of simple substances. The process can be divided into two types, igneous electrolysis and aqueous electrolysis. In this text we will emphasize only igneous electrolysis.
Igneous electrolysis is the process in which a molten (liquid) substance is subjected to an electric current, resulting in two new substances, one at the cathode (negative pole) and one at the anode (positive pole). In Carbon nanotube this is important now.
In igneous electrolysis, as in any electrolysis, the presence of free ions (cations and anions) in the medium is required. Cation is an electron-deficient ion, whereas anion is an ion with surplus electrons.
The ions present in the electrolyte tank (container where electrolysis occurs) come from the fusion (passage of a solid substance to the liquid state by heating) of an ionic substance (a salt or a base). Whenever this type of substance is subjected to heating, it undergoes dissociation (cation and anion release).
Ions from dissociation of an ionic compound
When an electric current reaches these ions, the cation receives electrons ( reduction ), and the anion loses its excess electrons ( oxidation ). In both reduction and oxidation of ions (X + and Y – ) we will have the formation of neutral substances (X and Y).
- General equations of ion reduction and oxidation
- Components of the igneous electrolysis system
The materials required for igneous electrolysis to occur are:
- A fused ionic substance (in liquid state)
- Electrolytic glass vat (can be, for example, an aquarium of any size)
- A source of electrical current (a battery, depending on the amount of substance that will be used in electrolysis)
- 2 electric wires
- Two inert electrodes (both graphite).
Chemical reactions of igneous electrolysis
As in a cell, when we perform igneous electrolysis, two reactions occur: one of oxidation and one of reduction:
Oxidation reaction (anodic reaction):
As in the cell, oxidation occurs at the anode. In this, the species that undergoes oxidation, that is, that loses electrons, will always be the anion. See the representation equation of this process:
Anion Oxidation Equation
In the equation, we have the anion before the arrow, and the simple substance and the electron after.
Reduction Reaction (Cathodic Reaction):
As in the cell, the reduction occurs at the cathode. In igneous electrolysis, the species that suffers reduction, that is, that gets electrons, will always be cation. See the representation equation of this process:
Cation Oxidation Equation
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In the equation, we have the cation and the electron before the arrow, and the simple substance after.
Example of igneous electrolysis
To illustrate, follow now the step-by-step process of igneous electrolysis of calcium iodide salt (CaI 2).
Melt the Salt
Initially it is necessary to fuse the salt so that it suffers the phenomenon of dissociation.
Salt Fusion Equation
In the case of calcium iodide, 1 mol of Ca + 2 cation and 2 mol of I- anion are released (because in the salt formula we have two iodines).
CaI 2 dissociation equation
Since the compound is ionic, therefore, the amount of one element will be the charge of the other element. Thus, we have index 2 on iodine, so the calcium charge is +2 as we have 1 in calcium, so the iodine charge is -1.