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chemistry igcse acapprinted 68 · PDF 68
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Alkaline Earth Metals (Group 2):
Always have an oxidation number of +2 in compounds.
Halogens (Group 17):
Generally have an oxidation number of -1.
Sum of Oxidation Numbers:
In a neutral compound, the sum of the oxidation numbers of all atoms must equal 0.
In a polyatomic ion, the sum of the oxidation numbers must equal the charge of the ion.
Examples of Assigning Oxidation Numbers:
Water (H₂O):
H: +1 (2 hydrogen atoms) → 2(+1) = +2
O: -2 → Total: +2 + (-2) = 0
Carbon Dioxide (CO₂):
C: +4 (since O is -2, total -4 from 2 O's, C must be +4)
O: -2 → Total: +4 + 2(-2) = 0
Oxidizing and Reducing Agents
Oxidizing Agent:
An oxidizing agent (oxidant) is a substance that gains electrons (is reduced) in a redox reaction,
causing the oxidation of another substance.
Characteristics:
Typically contains elements with high electronegativity (e.g., oxygen, halogens).
Increases its oxidation number.
Common Oxidizing Agents:
Potassium Permanganate (KMnO₄): Often used in redox titrations.
Hydrogen Peroxide (H₂O₂): Commonly used as a bleaching agent and disinfectant.
Chlorine Gas (Cl₂): Reacts with various compounds to oxidize them.
Example Reactions:
Chlorine Oxidizing Iron: 2Fe+Cl2→2FeCl2