3.2 d/f: Redox Reaction Basics

Redox Reactions

Year 11 Chem

​Syllabus dot points

• 3.2 d: ​apply the definitions of oxidation and reduction in terms of electron transfer and oxidation numbers to a range of reduction and oxidation (redox) reactions

​What we will cover

• ​oxidation and reduction

• redox reactions

​General Definition

• ​a reaction where one or more electrons are transferred from one atom to another

• oxidation = loss of electrons

• reduction = gain of electrons

• occur simultaneously, because the electrons must go somewhere. Therefore RedOx reaction

​Example:

​When magnesium metal reacts with oxygen gas and form solid magnesium oxide

• ​magnesium loses two electrons ​to become Mg²⁺ - so it is oxidised

• oxygen gains two electrons to become O^2- - so it is reduced

• ​therefore, a redox reaction

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​Half equations

• ​Singles out the oxidation and reduction within the overall reaction

• can be combined to form the overall net ionic equation

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Sometimes you have to balance the number of electrons

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​What would the balanced net ionic equation be for the half equations, knowing you have to balance the amount of electrons:

​Multiply the entire oxidation reaction by 3

Multiply the entire reduction reaction by 2 ​

​Oxidising and Reducing Agents

• oxidising agent = substance that makes oxidation occur in another substance (or the substance that gets reduced)

• reducing agent = substance that makes reduction occur in another substance (or the substance that gets oxidised)

• Example:

  • copper is reduced, and zinc is oxidised

  • therefore, copper is the oxidising agent, and zinc is the reducing agent ​

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Multiple Choice

If in a reaction, copper is reduced; its number of electrons has:

• Increased
• Decreased
• Remained Constant
• Varies Randomly

Multiple Choice

If an atom loses electrons during a chemical reaction, the atom was:

• Oxidized
• Reduced
• Neutralized
• Precipitated

Multiple Choice

Is calcium oxidized or reduced in the following reaction? 
2CaO--> 2Ca + O₂

• Oxidized
• Reduced

Multiple Choice

Given the oxidation-reduction reaction:

H₂ + 2 Fe⁺³ → 2 H⁺ + 2 Fe⁺²

Which species undergoes reduction?

• H₂

• Fe³⁺

• H⁺

• Fe²⁺

Multiple Choice

Given the cell reaction:

Ca(s) + Mg²⁺(aq) → Ca²⁺(aq) + Mg(s)

Which substance was oxidized?

• Ca(s)

• Mg²⁺(aq)

• Ca²⁺(aq)

• Mg(s)

Multiple Choice

In a redox reaction, the species reduced

• gains electrons and is the oxidizing agent

• gains electrons and is the reducing agent

• loses electrons and is the oxidizing agent

• loses electrons and is the reducing agent

Multiple Choice

Which half-reaction correctly represents oxidation?

• Sn²⁺ + 2e^– → Sn⁰

• Sn⁴⁺ + 2e^– → Sn²⁺

• Sn²⁺ → Sn⁰ + 2e^–

• Sn²⁺ → Sn⁴⁺ + 2e^–

​Up next:

• ​Oxidation numbers

• ​Galvanic cells