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CAIE A-Level Chemistry 6.1.1 Calculating Oxidation Numbers

Practise assigning oxidation numbers to atoms in elements, compounds and ions, including average and mixed oxidation states.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • apply fixed oxidation-number rules and make the sum equal the overall charge of the species
  • solve for an unknown or average oxidation number from the formula and charge balance
  • distinguish a fractional average oxidation state from the integer states present in a mixed oxide

6.1.1—Oxidation numbers of elements in compounds question 1

[Maximum number: 1]

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

A common test for nitrates is the reaction with NaOH and Al . Equation 1 shows the reaction.

 equation 13NO3−+8Al+5OH−+18H2O→3NH3+8[Al(OH)4]−\text { equation } 1 \quad 3 \mathrm{NO}_{3}^{-}+8 \mathrm{Al}+5 \mathrm{OH}^{-}+18 \mathrm{H}_{2} \mathrm{O} \rightarrow 3 \mathrm{NH}_{3}+8\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}

Deduce the oxidation state of nitrogen in NO3−\mathrm{NO}_{3}^{-}.

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