Complex Oxidation Numbers
15 Questions · 30 Marks · Mathematical Deduction
The Master Formula
Rule 1
Free element = 0
Rule 2
Neutral compound = 0
Rule 3
Ion = ion charge
O = −2 (always)
H = +1 (usually)
Group 1 = +1 always
Deduce the oxidation number of Sulfur in SO₂.
Deduce the oxidation number of Carbon in CH₄.
Deduce the oxidation number of Phosphorus in P₄O₁₀.
Deduce the oxidation number of Nitrogen in N₂O₄.
Deduce the oxidation number of Manganese in Mn₂O₇.
Deduce the oxidation number of Chromium in K₂Cr₂O₇.
Deduce the oxidation number of Sulfur in Na₂S₂O₃ (sodium thiosulfate).
Deduce the oxidation number of Nitrogen in (NH₄)₂SO₄.
Deduce the average oxidation number of Iron in Fe₃O₄.
Deduce the oxidation number of Hydrogen in CaH₂.
Deduce the oxidation number of Sulfur in the sulfate ion, SO₄²⁻.
Deduce the oxidation number of Nitrogen in the nitrate ion, NO₃⁻.
Deduce the oxidation number of Manganese in the permanganate ion, MnO₄⁻.
Deduce the oxidation number of Chromium in the dichromate ion, Cr₂O₇²⁻.
Deduce the oxidation number of Phosphorus in the pyrophosphate ion, P₂O₇⁴⁻.
Examiner's Summary
Most Common Mistakes
- → Setting ion equations equal to 0
- → Forgetting to divide by number of atoms
- → Assuming H is always +1
Mark Scheme Language
- → Show algebraic working clearly
- → State the ion charge used
- → Include + or − sign in answer
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