Example Question 1

Edexcel AS-level ChemistryOxidation and ReductionLesson 6 of 14

Question: Work out the oxidation number of (a) manganese in MnO₄⁻, (b) chromium in Cr₂O₇²⁻ and (c) sulfur in S₂O₃²⁻.

Method: give each element you know a fixed value first. Oxygen is −2 (none of these is a peroxide). Then use the rule that the oxidation numbers in an ion add up to the charge on the ion. Call the unknown x.

(a) MnO₄⁻: four oxygens give 4 × (−2) = −8.

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Key terms in this lesson

oxidation number: A number assigned to an atom showing its degree of oxidation, based on the electrons it would gain or lose if all bonds were ionic.

Example Question 1

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Key terms in this lesson

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