Redox

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Notes

Oxidation & Reduction in Terms of Oxygen

**Oxidation** is the **addition of oxygen** to an element or compound.
**Reduction** is the **removal of oxygen** from an element or compound.
A **redox reaction** involves both oxidation and reduction occurring simultaneously.
Example: $ZnO + C$ → $Zn + CO$ – zinc oxide is reduced (loses oxygen), carbon is oxidised (gains oxygen).

Oxidation & Reduction in Terms of Electrons (Extended)

**Oxidation** is the **loss of electrons**; the oxidation number increases.
**Reduction** is the **gain of electrons**; the oxidation number decreases.
Mnemonic: **OIL RIG** – **O**xidation **I**s **L**oss, **R**eduction **I**s **G**ain.
Half-equations show electron transfer, e.g. Ag → Ag⁺ + e⁻ (oxidation) and O₂ + 4e⁻ → 2O²⁻ (reduction).

Oxidation Numbers & Roman Numerals

Transition metals can form ions with different charges; the charge is shown by a **Roman numeral** in the name.
The Roman numeral equals the **oxidation number** of the metal ion.
Example: Fe²⁺ is **iron(II)**; Fe³⁺ is **iron(III)**.
Example: FeO is iron(II) oxide; Fe₂O₃ is iron(III) oxide.
In CoCl₂, chloride ions are each 1−, so cobalt is 2+ → **cobalt(II) chloride**.

Identifying Redox Reactions

In a redox reaction, one species is oxidised and another is reduced.
Example: Fe₂O₃ + 3CO → 2Fe + 3CO₂ – Fe₂O₃ is reduced (loses oxygen), CO is oxidised (gains oxygen).
In ionic equations, spectator ions are removed to show the redox change.
Example: Fe + Cu²⁺ → Fe²⁺ + Cu – Fe is oxidised (loses electrons), Cu²⁺ is reduced (gains electrons).

Atomic structure of iron (Fe). The electron configuration shows the arrangement of electrons in shells. Iron can lose 2 electrons (Fe²⁺) or 3 electrons (Fe³⁺), corresponding to oxidation numbers II and III.

Practice questions

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1.In a redox reaction, oxidation and reduction occur separately, not together.
Easy
True or false?
2.State the meaning of the mnemonic OIL-RIG in terms of electron transfer.
Easy
3.In the reaction between zinc oxide and carbon, which substance is reduced?
Easy
- Azinc oxide
- Bcarbon
- Czinc
- Dcarbon dioxide
4.Complete the sentence using the words 'oxidation' or 'reduction'.
Medium
In terms of oxygen, $____ is$ the gain of oxygen $and ____ is$ the loss of oxygen.
5.What is the oxidation number of the transition metal in silver(I) chloride, AgCl?
Medium
6.What is the oxidation number of cobalt in cobalt(II) chloride, CoCl2?
Medium
- A1
- B3
- C4
- D2
7.In the reaction $Fe + CuSO4$ → $FeSO4 + Cu$ , the iron atom is reduced.
Medium
True or false?
8.In the reaction $V^{3}+ + Fe^{3}+$ → $V^{4}+ + Fe^{2}+$ , which species is oxidised?
Hard

Slides

Oxidation & Reduction in Terms of Oxygen

Oxidation is the gain of oxygen by a substance.
Reduction is the loss of oxygen from a substance.
A redox reaction is one where both oxidation and reduction occur together.

In the reaction: $ZnO + C$ → $Zn + CO$ , which substance is reduced?

Zinc oxide
Carbon
Zinc
Carbon monoxide

Oxidation Numbers & Roman Numerals

Transition metals can form ions with different charges, shown by Roman numerals.
The Roman numeral gives the oxidation number of the metal.
For example, Fe²⁺ is iron(II) and Fe³⁺ is iron(III).

What is the oxidation number of cobalt in cobalt(III) chloride?

Redox in Terms of Electron Transfer (Extended)

Oxidation is the loss of electrons.
Reduction is the gain of electrons.
Use OIL RIG: Oxidation Is Loss, Reduction Is Gain.

In the reaction Fe + Cu²⁺ → Fe²⁺ + Cu, iron $is ____$ because $it ____$ electrons.

Half-Equations

Half-equations show electron loss or gain separately.
Oxidation half-equation: Ag → Ag⁺ + e⁻
Reduction half-equation: O₂ + 4e⁻ → 2O²⁻

Which half-equation represents reduction?

Mg → Mg²⁺ + 2e⁻
Cl₂ + 2e⁻ → 2Cl⁻
Cu → Cu²⁺ + 2e⁻
Fe²⁺ → Fe³⁺ + e⁻

Identifying Redox Reactions

In a redox reaction, one species is oxidised and another is reduced.
Example: Fe + CuSO₄ → FeSO₄ + Cu
Ionic equation: Fe + Cu²⁺ → Fe²⁺ + Cu

Which of these are true about the reaction Fe + Cu²⁺ → Fe²⁺ + Cu?

Iron is oxidised.
Copper(II) ions are reduced.
Iron gains electrons.
Copper(II) ions lose electrons.

Worked Example: Oxidation State Changes

Consider: V³⁺ + Fe³⁺ → V⁴⁺ + Fe²⁺
V³⁺ loses an electron to become V⁴⁺ (oxidation).
Fe³⁺ gains an electron to become Fe²⁺ (reduction).

In the change V³⁺ → V⁴⁺, what happens?

Oxidation, because it loses an electron
Reduction, because it gains an electron
Oxidation, because it gains an electron
Reduction, because it loses an electron

Flashcards

What is a redox reaction?

A redox reaction is where oxidation and reduction take place together at the same time in the same reaction.

Define oxidation in terms of oxygen.

Oxidation is the addition of oxygen to an element or a compound.

Define reduction in terms of oxygen.

Reduction is the removal of oxygen from an element or a compound.

Define oxidation in terms of electron transfer (extended tier).

Oxidation is the loss of electrons by an element, ion or compound; the oxidation number increases.

Define reduction in terms of electron transfer (extended tier).

Reduction is the gain of electrons by an element, ion or compound; the oxidation number decreases.

What does the mnemonic OIL-RIG stand for?

Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

In the reaction $Fe2O3 + 3CO$ → $2Fe + 3CO2$ , which substance is oxidised and which is reduced?

Carbon monoxide is oxidised (gains oxygen), iron(III) oxide is reduced (loses oxygen).

What is the oxidation number of the transition metal in silver(I) chloride, AgCl?

The oxidation number is 1 (the Roman numeral I indicates +1).

Name the compound with formula CoCl2 using Roman numerals.

Cobalt(II) chloride.

Write the half-equation for the oxidation of silver to silver ions.

Ag → $Ag+ + e-$

Write the half-equation for the reduction of oxygen to oxide ions.

$O2 + 4e-$ → 2O2-

In the reaction $Fe + CuSO4$ → $FeSO4 + Cu$ , which species is oxidised and which is reduced?

Iron is oxidised (loses electrons to become Fe2+), copper(II) ions are reduced (gain electrons to become Cu).

Write the ionic equation for the displacement reaction between iron and copper(II) sulfate, removing spectator ions.

$Fe + Cu2+$ → $Fe2+ + Cu$

In the reaction $V3+ + Fe3+$ → $V4+ + Fe2+$ , which species is oxidised?

V3+ is oxidised to V4+ (loses one electron).

What is the oxidation number of iron in iron(II) oxide?

+2 (iron(II) indicates Fe2+).

What is the formula of iron(III) oxide?

Fe2O3.

What is the formula of iron(II) oxide?

FeO.

How do you show the oxidation number of a transition metal in a compound name?

Use a Roman numeral in parentheses after the element's name, e.g., iron(III) chloride.

What is the oxidation number of cobalt in cobalt(II) chloride?

+2 (since two chloride ions each have -1 charge, cobalt must be +2).

In terms of oxygen, what happens to zinc oxide in the reaction $ZnO + C$ → $Zn + CO$ ?

Zinc oxide is reduced because it loses oxygen.

In terms of oxygen, what happens to carbon in the reaction $ZnO + C$ → $Zn + CO$ ?

Carbon is oxidised because it gains oxygen.

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