To understand electrochemistry, it is necessary to know how to calculate the oxidation number of the substances involved in a chemical reaction.
The oxidation number or NOX shall be calculated as follows:
1) Simple Substance: ZERO (because there is no loss and no gain of electrons).
H2 NOX H = 0
Fe NOX Fe = 0
O3 NOX O = 0
2) Atom as simple ion: Your own charge.
Na + NOX Na = 1+
s2- NOX S = 2-
H + NOX H = 1+
3) Alkali metals to the left of the formula: 1+
NaCl NOX Na = 1+
LiF NOX Li = 1+
K2S NOX K = 1+
4) Alkaline earth metals to the left of the formula: 2+
CaO NOX Ca = 2+
MgS NOX Mg = 2+
SrCl2 NOX Sr = 2+
5) Halogens: 1-
NaCl NOX Cl = 1-
KF NOX F = 1-
K2Br NOX Br = 1-
6) Chalcogens: 2-
CaO NOX O = 2-
ZnO NOX O = 2-
MgS NOX S = 2-
7) Ag, Zn and Al: 1+, 2+, 3+
AgCl NOX Ag = 1+
ZnS NOX Zn = 2+
Al2s3 NOX Al = 3+
8) Hydrogen in compound: 1+
H2NOX H = 1+
9) Metal hydride (hydrogen on the right side of the formula): 1-
NaH NOX H = 1-
10) Oxygen in compound (calcogen rule): 2-
H2NOX O = 2-
11) Fluorine oxygen: 1+ and 2+
O2F2 NOX O = 1+
OF2 NOX O = 2+
12) Peroxides (oxygen + alkaline / alkaline earth): 1-
H2O2 NOX 0 = 1-
At2NOX 0 = 1-
13) Superoxides: -
K2O4 NOX O = -
For substances with two or more chemical elements:
- sum of NOX of all atoms = zero
- sum of NOX of all atoms in a compound ion = their charge
Example: To find NOX of H in the water, knowing only NOX of O, you can place on top of the formula NOX and below the sum. Like this:
1+ 2- → NOX
H2O → chemical element
2+ 2- = 0 → summation
In this case, O's NOX is 2-. NOX is multiplied by the number of O atoms, so 2-
Since water is a substance that is in its neutral state (not an ion), the sum of charges is zero. H adds 2+ for this reason.
To find the NOX of H, divide the sum of H by the number of H atoms. Since there are two H atoms, NOX will be 1+
It is the chemical reaction that is characterized by the loss or gain of electrons. It is the transfer of electrons from one chemical species to another. Two phenomena occur: oxidation and reduction.
Oxidation - electron loss, where NOx increases. Reducing agent.
Reduction - electron gain, where NOX decreases. Oxidizing agent.