Oxidation And Reduction Reaction SS2 Chemistry Lesson Note

The following definitions have been used for the oxidation and reduction processes.

1. In Terms Of Oxygen: Oxidation is defined as the addition of oxygen to a substance while reduction is defined as the removal of oxygen from a substance. Examples:

2Mg(s)+ O2(g) > 2MgO(s)

2. In Terms Of Hydrogen: Oxidation is defined as the removal of hydrogen from a substance while reduction is the addition of hydrogen to a substance. Example:

H2S(g) + Cl2(g) > 2HCl(g) + S(s)

3. In Terms Of Electronegative Elements: Oxidation is defined as the addition of an electronegative element to a substance while reduction is the removal of an electronegative element from a substance. Example:

Na (s) + Cl2(g) > NaCl(s)

4. In terms of Electron Transfer: Oxidation is defined as the loss of an electron from substances while reduction is defined as the gain of electrons by a substance. Example:

FeCl2 (s) + Cl2 (g) > FeCl3(s)

RELATIONSHIP BETWEEN OXIDATION NUMBER AND IUPAC NAMING

The oxidation number or state of an element in a neutral compound or radical (ion) is defined as the numerical electrical charge it appears to have as determined by a set of arbitrary rules.

RULES OF DETERMINING OXIDATION NUMBERS

1. The oxidation number of all uncombined elements is zero e.g. Na, Cl.
2. The oxidation number of an ion consisting of a single element is the same as the ionic charge on it. E.g. The oxidation number of Nat is +1, Cl is -1.
3. The oxidation number of an ion consisting of more than one element (radical) is the algebraic sum of the oxidation number of all the elements in the ion.
4. The oxidation number of a neutral compound is zero and it is the algebraic sum of the oxidation number of all the elements in the compound.

Example 1:

Find the oxidation number of the manganese atom in KMnO4 and give the IUPAC name of the compound.

Solution:

KMnO4 = 0

(+1) + Mn +4(-2) =0

+1+Mn-8=0

Mn-7=0

Mn = +7

The oxidation number (state) of manganese in KMnO4 is + 7.

Hence the IUPAC name of the compound is Potassium tetraoxomanganate (VII)

IDENTIFYING REDOX REACTIONS USING OXIDATION NUMBER

Redox reactions can be identified with the aid of oxidation numbers. For a redox reaction, the oxidation number of an element on the reactant side is different on the product side. There must be changes in oxidation numbers.