4CH1

The Reactivity Series

Inorganic Chemistry · 1 question type

Practise

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable
Low
Stable6%

Displacement reactions and determining order of reactivity from experimental data.

In terms of oxygen

  • Oxidation is the gain of oxygen by a substance
  • Reduction is the loss of oxygen from a substance
  • The two always happen together in the same reaction — a redox reaction
  • In Zn + CuO → ZnO + Cu:
    • Zinc gains oxygen → zinc is oxidised → zinc is the (it caused the reduction of CuO)
    • Copper(II) oxide loses oxygen → it is reduced → CuO is the

In terms of electrons

  • The more general definitions use electron transfer:
    • is loss of electrons
    • is gain of electrons
  • Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain)
OIL RIG memory aid: Oxidation Is Loss of electrons, Reduction Is Gain of electrons
Source: Oxidation and reduction by Save My Exams
  • For the displacement reaction Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s):
    • Mg → Mg2+ + 2 e− (oxidation — Mg loses electrons)
    • Cu2+ + 2 e− → Cu (reduction — Cu2+ gains electrons)
  • Mg is the reducing agent (gives away electrons); Cu2+ is the oxidising agent (accepts them)
Displacement of copper by iron as a redox reaction: iron is oxidised to Fe²⁺ while Cu²⁺ is reduced to copper metal
Source: Oxidation and reduction by Save My Exams
Exam tip

Explaining why a displacement reaction is redox (two marks)

What comes up: a two-mark question asks you to explain why a metal displacement reaction (for example, aluminium reducing iron oxide) is a redox reaction.

Write (two marks): (1) one substance gains oxygen (or loses electrons) and is oxidised — state which one. (2) the other substance loses oxygen (or gains electrons) and is reduced — state which one. For example: aluminium gains oxygen and is oxidised; iron(III) oxide loses oxygen and is reduced.

Watch out: the mark scheme rejects "iron loses oxygen" as the description of what is reduced — it is iron(III) oxide (the compound) that loses oxygen, not iron itself. Name the compound, not the metal element.

Spectator ions and ionic equations

  • In the full equation Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s), the sulfate ion SO42− appears on both sides unchanged
  • An ion that is unchanged in a reaction is a spectator ion — it does not take part in the chemistry
  • Leaving out the spectator ions gives the ionic equation, which highlights the actual redox change: Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)

A practice prompt

  • In the reaction Cu(s) + 2 AgNO3(aq) → Cu(NO3)2(aq) + 2 Ag(s), Cu loses two electrons to form Cu2+ (oxidation) while each Ag+ gains one electron to form Ag (reduction)
  • Copper is therefore the reducing agent here, and silver(I) is the oxidising agent