Oxidation numbersEdexcel A-Level Chemistry: Mind map

Exam questions on Oxidation numbers

1. A technician is relabelling reagent bottles in a school store room. The bottles are marked only with the formulae KMnO₄, Fe₂O₃, H₂O₂ and CaH₂, and she must add the correct oxidation numbers to each label.
   Explain why the oxidation numbers of oxygen in H₂O₂ and of hydrogen in CaH₂ differ from the values these elements usually have.2 marks
2. Sulfur forms many compounds and ions in which its oxidation number ranges from −2 to +6.
   Calculate the oxidation number of sulfur in the thiosulfate ion, S₂O₃²⁻. Show your working.2 marks
3. Nitrogen forms compounds and ions in which its oxidation number ranges from −3 to +5. An environmental chemist is studying nitrogen species found in air and in rainwater.
   Calculate the oxidation number of nitrogen in NH₄⁺, in N₂O and in NO₃⁻.3 marks