Magnetite, Fe₃O₄, is a common ore of iron. Calculate the average oxidation state of iron in the compound and comment on your answer.

State the equation for the reduction of this ore to iron with carbon monoxide.

Outline why iron is obtained from its ores using chemical reducing agents but aluminium is obtained using electrolysis.

\( + \frac{8}{3}/ + 2\frac{2}{3}\) ;

Accept +2.7 but not +3.

+2 and +3 / contains two (or more) iron ions with different oxidation states / contains \({\text{F}}{{\text{e}}^{{\text{2}} + }}\) and \({\text{F}}{{\text{e}}^{{\text{3}} + }}\);

Accept II and III oxidation number notation for oxidation states but not 2+ and 3+ unless ions are referred to explicitly.

Accept “contains different iron compounds/FeO and Fe₂O₃”.

\({\text{F}}{{\text{e}}_3}{{\text{O}}_4}{\text{(s)}} + {\text{4CO(g)}} \to {\text{3Fe(l)}} + {\text{4C}}{{\text{O}}_2}{\text{(g)}}\);

Accept “Fe₃O₄(s) + CO(g) \( \to \) 3FeO(s) + CO₂(g) and

FeO(s) + CO(g) \( \to \) Fe(l ) + CO₂(g)”.

Ignore state symbols.

Al is more reactive than Fe / Al is higher than Fe in the reactivity series / Al is a stronger reducing agent / it is harder to reduce aluminium ores compared to iron ores / \({\text{F}}{{\text{e}}^{3 + }}/{\text{F}}{{\text{e}}^{2 + }}\) is a stronger oxidizing agent / \({\text{A}}{{\text{l}}^{3 + }}\) has a very negative E° value;

This was a challenging question but some candidates managed to calculate the average oxidation state of iron as +8/3, and very few were able to deduce that both +2 and +3 oxidation states were present in the ore.

It was disappointing that most candidates could not give a correct equation for the reduction, considering that both reactants and one product are already given in the question.

Some candidates gave the higher reactivity of aluminium as the reason why it could not be extracted by the use of reducing agents.