What this standard actually asks for

How this standard is assessed

• AS91167 is internally assessed — there is no external exam for it, so there are no past papers to work through. What there is instead is a fixed, published list of what can be assessed, and you can prepare against that list exactly.
• The standard limits oxidation–reduction to six things. Nothing outside this list can be assessed.

The six things you can be assessed on

What	What you must be able to do
Oxidation numbers	Assign an oxidation number to any atom in a formula, and spot which ones change
Electron transfer	Say which species lost electrons and which gained them, and how many
Oxidants and reductants	Name the oxidant (the species reduced) and the reductant (the species oxidised)
Observations	Describe what you would see — colours, precipitates, gases, a metal coating
Half equations	Write a balanced half equation for the oxidation and one for the reduction
Overall equations	Combine the two halves into a balanced overall equation with no electrons left in it

How the grades are separated

• Achieved — identify the species and say whether each is oxidised or reduced, with a reason.
  • The reason is either electrons lost/gained or a change in oxidation number. Without a reason, it is not Achieved.
• Merit — write balanced half equations, and link them to the observations.
  • "The purple MnO₄⁻ was reduced to colourless Mn²⁺, shown by the half equation …" is the shape of a Merit sentence.
• Excellence — bring the half equations, the overall equation, the observations and the electron transfer together into one justified account.
  • Excellence is not "more facts". It is the same facts, connected.

What is NOT in this standard

Do not spend time on these — they belong to Level 3 (AS91393):

• Standard reduction potentials ($E°$ values) and cell potentials.
• Predicting whether a reaction is spontaneous from $E°$.
• Electrochemical and electrolytic cells, salt bridges, electroplating.

Also outside this standard: redox titration calculations, and balancing half equations in basic solution. Everything here is balanced in acidic solution using H⁺ and H₂O.

What your assessment will look like

• You are given a set of reactions, often with observations recorded from a practical you have done.
• You are usually given a table of substances: name, formula and appearance.
• That table is not allowed to pair them up for you — matching an oxidant with a reductant is the part being assessed.
• You then explain each reaction: what was oxidised, what was reduced, the half equations, the overall equation, and how the observations show it.

The species you should know on sight

The standard names the substances that can appear. These are the ones worth knowing cold:

• Oxidants — O₂, I₂, Br₂, Cl₂, OCl⁻, H⁺, Fe³⁺, Cu²⁺, H₂O₂, MnO₄⁻ in acid, Cr₂O₇²⁻ in acid, concentrated HNO₃, IO₃⁻.

• Reductants — metals, C, H₂, Fe²⁺, Br⁻, I⁻, H₂S, SO₂, SO₃²⁻, HSO₃⁻, H₂O₂.

• Note that H₂O₂ appears on both lists. Hydrogen peroxide can act as either, depending on what it meets — that is a favourite Excellence question, and it has its own page later in this topic.