Reactivity Series
5 marks · EasyA student heats a mixture of powdered aluminium and iron(III) oxide. The following reaction occurs:
Use the reactivity series to explain why this reaction occurs. Identify which metal is displaced and why.
In terms of electron transfer, describe what happens to aluminium and what happens to iron(III) oxide in the reaction above. Use your answer to part (a) to help you.
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(a) Aluminium is more reactive than iron, so aluminium displaces iron from iron(III) oxide. Iron is the metal displaced. This reaction occurs because a more reactive metal (aluminium) will displace a less reactive one (iron) from its oxide. · must show Aluminium is more reactive than iron, Aluminium displaces iron from Fe2O3, Iron is the metal displaced, Reference to the reactivity series
(b) Aluminium atoms lose electrons to form Al3+ ions (aluminium is oxidised). Iron(III) ions in Fe2O3 gain electrons to form Fe atoms (iron(III) oxide is reduced). Thus, aluminium acts as the reducing agent and iron(III) oxide as the oxidising agent. · must show Aluminium atoms lose electrons (oxidised), Iron(III) ions gain electrons (reduced), Identifies which is oxidising/reducing agent
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Marking points
M1 (a) · 1 mark · Correctly refers to the reactivity series: aluminium is more reactive than iron.
A1 (a) · 1 mark · Identifies iron as the displaced metal and explains why displacement occurs.
M2 (b) · 1 mark · Describes aluminium atoms lose electrons to become ions (oxidised).
M3 (b) · 1 mark · Describes iron(III) ions gain electrons to become atoms (reduced).
B1 (b) · 1 mark · Identifies aluminium as reducing agent and iron(III) oxide as oxidising agent, or clearly links loss/gain of electrons to these roles.
Worked solution
a) Aluminium is higher than iron in the reactivity series, so it is more reactive than iron. When aluminium and iron(III) oxide are heated together, aluminium displaces iron from the oxide, forming aluminium oxide and iron. The iron in the iron(III) oxide is the metal displaced.
b) In terms of electron transfer: aluminium atoms each lose three electrons to become Al$^{3+}$ ions (oxidation). Iron(III) ions (Fe$^{3+}$) in Fe$_2$O$_3$ each gain three electrons to become iron atoms (reduction).
Therefore, aluminium is the reducing agent (it gives electrons), and iron(III) oxide is the oxidising agent.