6.2.3Additional lessons
Relative Ease of Oxidation and Reduction — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 134 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Metal Reactivity
Ease of oxidation is the tendency of a species to lose electrons.
Reactivity series
- Reactivity series Metals are ranked by how readily they lose electrons, with potassium at the top and silver or gold near the bottom.
Strong reducing agent
- Strong reducing agent A reactive metal such as magnesium is easily oxidised, so it is a good reducing agent.
Weak reducing agent
- Weak reducing agent An unreactive metal such as silver resists oxidation, so its ions are easily reduced to the metal.
Link to ions
- Link to ions The more easily a metal is oxidised, the less easily its ion is reduced back to the metal.
Section 2 of 5Displacement Reactions
1
Place a strip of a metal in a solution containing ions of another metal and observe whether a deposit forms.
2
If the metal is more reactive it loses electrons to the ions in solution, so the ions are reduced to solid metal.
3
For example Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), and a pink-brown deposit of copper appears on the zinc.
4
If the metal is less reactive nothing happens, because its atoms cannot reduce the ions of the more reactive metal.
5
Ranking the metals from many such experiments builds the reactivity series.
Section 3 of 5Halogen Displacement
Halogen Displacement
Oxidising power
- Oxidising power Down Group 17 halogens become weaker oxidising agents, so Cl₂ is stronger than Br₂ and Br₂ is stronger than I₂.
Chlorine and bromide
- Chlorine and bromide Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq), and the solution turns orange as bromine forms.
Bromine and chloride
- Bromine and chloride No reaction occurs because bromine is too weak an oxidising agent to oxidise chloride ions.
Halide ions
- Halide ions Down the group halide ions become stronger reducing agents, so I⁻ is oxidised most easily.
| Halogen | Oxidising ability | Halide | Reducing ability |
|---|---|---|---|
| Cl₂ | Strongest | Cl⁻ | Weakest |
| Br₂ | Intermediate | Br⁻ | Intermediate |
| I₂ | Weakest | I⁻ | Strongest |
Section 4 of 5Worked Example
Question Predict whether iron will displace copper from copper(II) sulfate solution and write the ionic equation.
- Iron is more reactive than copper, so Fe loses electrons more easily than Cu.
- Fe is oxidised to Fe²⁺ and Cu²⁺ is reduced to Cu, so a displacement reaction occurs.
- Cancel the sulfate spectator ions to get the ionic equation.
Answer Yes: Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)
Section 5 of 5Exam Checklist & Tips
6.2.3 – Key Points for the Exam
- Reactivity series A list of metals in order of their tendency to lose electrons and form positive ions.
- Displacement reaction A reaction in which a more reactive element removes a less reactive element from its compound.
- Reducing agent A species that readily donates electrons, such as a reactive metal.
- Oxidising agent A species that readily accepts electrons, such as chlorine.
Common Mistakes
- Saying that a more reactive metal is a better oxidising agent; it is a better reducing agent.
- Predicting a halogen will displace a halide above it in the group, which does not happen.
- Forgetting that displacement is a redox reaction and writing no electron transfer.
- Mixing up the species oxidised and the species reduced in displacement equations.
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