Overview
This lecture introduces redox reactions, covering definitions, displacement reactions, ionic equations, and half equations, and explains how oxidation and reduction involve electron transfer.
Redox Reactions: Basics
- Redox reactions involve both oxidation and reduction occurring simultaneously.
- Oxidation can mean gaining oxygen or losing electrons.
- Reduction can mean losing oxygen or gaining electrons.
- The mnemonic "OIL RIG" helps remember: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
- In a redox process, if one substance loses electrons, another must gain those electrons.
Examples of Redox Reactions
- When magnesium reacts with acid (H⁺), magnesium is oxidized (loses electrons), and hydrogen ions are reduced (gain electrons) to form hydrogen gas.
- Displacement reactions are redox reactions where a more reactive metal displaces a less reactive metal from a compound.
Displacement Reactions & Ionic Equations
- A more reactive metal (e.g., calcium) will displace a less reactive one (e.g., iron) from its compound (e.g., iron sulfate).
- Ionic equations show only the ions that change during the reaction, omitting spectator ions (ions that do not change).
- Spectator ions, like sulfate (SO₄²⁻), are not included in the simplified ionic equation.
Half Equations
- Half equations represent oxidation or reduction for a single element, showing electron loss or gain.
- For calcium: Ca → Ca²⁺ + 2e⁻ (shows loss of electrons, oxidation).
- For iron: Fe²⁺ + 2e⁻ → Fe (shows gain of electrons, reduction).
- Charges on both sides of a half equation must balance; this checks equation correctness.
Key Terms & Definitions
- Redox Reaction — A chemical reaction involving both oxidation and reduction.
- Oxidation — Loss of electrons (or gain of oxygen).
- Reduction — Gain of electrons (or loss of oxygen).
- Ionic Equation — An equation showing only the reacting ions, not spectator ions.
- Spectator Ion — An ion that does not change during a reaction.
- Half Equation — An equation showing electron gain or loss for a single species.
Action Items / Next Steps
- Review how to write ionic and half equations for sample reactions.
- Practice identifying oxidation and reduction in provided chemical reactions.