How to format the answers for NCEA redox

char1otte · 18 February 2022 23:34

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

ben.moe · 22 February 2022 03:42

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.

MnO_4^- + 8H⁺ + 5e → Mn²⁺ + 4H₂O

5Fe²⁺ → 5Fe³⁺ + 5e

MnO_4^- + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 4H₂O + 5Fe³⁺

MnO_4^- is the species that is reduced, therefore MnO_4^- is the oxidant (since it is reduced)

Each MnO_4^- gains five electrons, and the Mn in the MnO_4^- has an oxidation number of +7 and this decreases to +2 in Mn²⁺, so the MnO_4^- 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!