How to format the answers for NCEA redox

Please could you give an example using any species of how you would format an answer to this. These are the questions:

  • Identify the species that is oxidised and the one that is reduced
  • Identify the oxidant and reluctant with reasons

Kia ora!

For example:

When fresh iron (II) sulfate solution is added to acidified potassium permanganate solution, a pale green solution and a purple solution react to form an orange solution.

MnO4- + 8H+ + 5e → Mn2+ + 4H2O

5Fe2+ → 5Fe3+ + 5e

MnO4- + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+

MnO4- is the species that is reduced, therefore MnO4- is the oxidant (since it is reduced)

Each MnO4- gains five electrons, and the Mn in the MnO4- has an oxidation number of +7 and this decreases to +2 in Mn2+, so the MnO4- is reduced to Mn2+ therefore it is the oxidant.

Fe2+ is the species that is oxidised, therefore Fe2+ is the reductant (since it is oxidised).

Each Fe2+ loses one electron. The oxidation number of Fe in Fe2+ is 2 and this increases to 3 in Fe3+, so the Fe2+ is oxidised to Fe3+ therefore it is the reductant.

Note - the reason given to support identification of the oxidant or reductant could be the change in oxidation number, or the loss or gain of electrons – the example above includes both reasons.

Good luck!