Chemistry

Oxidation Number (NOX)


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).
Examples:
H2 NOX H = 0
Fe NOX Fe = 0
O3 NOX O = 0

2) Atom as simple ion: Your own charge.
Examples:
Na + NOX Na = 1+
s2- NOX S = 2-
H + NOX H = 1+

3) Alkali metals to the left of the formula: 1+
Examples:
NaCl NOX Na = 1+
LiF NOX Li = 1+
K2S NOX K = 1+

4) Alkaline earth metals to the left of the formula: 2+
Examples:
CaO NOX Ca = 2+
MgS NOX Mg = 2+
SrCl2 NOX Sr = 2+

5) Halogens: 1-
Examples:
NaCl NOX Cl = 1-
KF NOX F = 1-
K2Br NOX Br = 1-

6) Chalcogens: 2-
Examples:
CaO NOX O = 2-
ZnO NOX O = 2-
MgS NOX S = 2-

7) Ag, Zn and Al: 1+, 2+, 3+
Examples:
AgCl NOX Ag = 1+
ZnS NOX Zn = 2+
Al2s3 NOX Al = 3+

8) Hydrogen in compound: 1+
Example:
H2NOX H = 1+

9) Metal hydride (hydrogen on the right side of the formula): 1-
Example:
NaH NOX H = 1-

10) Oxygen in compound (calcogen rule): 2-
Example:
H2NOX O = 2-

11) Fluorine oxygen: 1+ and 2+
Examples:
O2F2 NOX O = 1+
OF2 NOX O = 2+

12) Peroxides (oxygen + alkaline / alkaline earth): 1-
Examples:
H2O2 NOX 0 = 1-
At2NOX 0 = 1-

13) Superoxides: -
Example:
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+

Oxeduction

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.