SS2 Third Term Chemistry Lesson Note – Oxidation – Reduction (Redox) Reaction

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WEEK 2

TOPIC: OXIDATION – REDUCTION (REDOX) REACTION

CONTENT: 1. OXIDATION AND REDUCTION

1. Redox reactions
2. Oxidation numbers of central element in some compounds
3. Connection of oxidation number with IUPAC name
4. Oxidizing and reducing agents
5. Redox equation

PERIOD 1: OXIDATION AND REDUCTION

Redox is a short form for reduction and oxidation reactions. The two reactions are opposing and complementary and they occur simultaneously. Redox has the following definitions

1. Definition of Oxidation reactions with examples

• In terms of addition of oxygen: Oxidation is the addition of oxygen or removal of hydrogen from a substance. Any reaction where there is addition of oxygen to a reactant is regarded as Oxidation.

Some examples are:

(i) 2Mg_(s) + O_2(g)    →     2MgO_(s)           oxidation of magnesium

(ii) C_(s) + 2ZnO_(s)      →       CO_{2 (g)} + 2Zn_(s)

In this reaction, oxygen (O) was added to carbon (C) to form Carbon (iv) oxide (CO₂). That is carbon was oxidized to Carbon (iv) oxide.

• In terms of hydrogen removal: Oxidation is the removal of hydrogen from a compound e.g. (i) combustion of hydrogen sulphide

2H₂S_(g) + O_2(g)   →    2H₂O_(l) + 2S_(s)

H₂S_(g) + Cl_2(g)     →   2HCl_2(g) + S_(s)

In both reactions, hydrogen sulphide was oxidized to Sulphur. The second reaction shows that oxidation can occur without the involvement of oxygen

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