REDOX

Redox Overview

• Definition:

  • REDOX is an abbreviation for REDuction/OXidation.

• Key Concepts:

  • Oxidation refers to a loss of electrons, which results in an increase in oxidation state.

  • Example Reaction:

    • Calcium atom (Ca) is oxidized to Calcium ion (Ca²⁺):

    • Ca⁰ 🡪 Ca²⁺

  • Reduction refers to a gain of electrons, leading to a decrease in oxidation state.

  • Example Reaction:

    • Sulfur atom (S) is reduced to Sulfide ion (S²⁻):

    • S⁰ 🡪 S²⁻

• Mnemonic Device:

  • The phrase LEO says GER can help remember the definitions of oxidation and reduction:

  • LEO: Loss of Electrons = Oxidation

  • GER: Gain of Electrons = Reduction

Oxidation Numbers

• Definition:

  • An oxidation number represents the hypothetical charge an atom would have if all bonds to atoms of different elements were fully ionic.

• Examples of Oxidation Numbers:

  • Chlorine (Cl) has an oxidation number of -1.

  • Hydrogen (H) has an oxidation number of +1.

• Difference from Actual Charge:

  • Oxidation numbers are similar to charges but are not the same.

• Key Concept in Redox:

  • Redox processes involve TRANSFERRING ELECTRONS and ensuring charge and oxidation states are balanced.

Practice with Oxidation Numbers

• Given Set of Charges:

  • Practice recognizing oxidation states for compounds with the following numbers:

  • +1, +1, -2, +5, -6, +5, +1, +2, -2, +12, -14, +6

  • +1, +6, -2, -4, -2, -2, -1, +1, -1, +1

• Compound Examples:

  • HNO₃, C₂H, K₂Cr₂O₇, 6O, AgI

  • Oxidation States:

  • +1, +2, -2, +5, -8, +5, H₂PO₄

Half-Reactions in Redox

• Example Reaction:

  • Calcium Chloride (CaCl₂) as an ionic compound breakdown:

  • Reactants:

    • Calcium (Ca⁰) and Chlorine (Cl₂) leading to products:

    • Ca + Cl₂ → CaCl₂

  • Half-Reaction for Calcium Oxidation:

  • Ca⁰ → Ca²⁺ + 2e⁻

  • Half-Reaction for Chlorine Reduction:

  • Cl₂⁰ + 2e⁻ → 2Cl⁻

  • Summary:

  • Oxidation: Calcium is losing electrons.

  • Reduction: Chlorine is gaining electrons.

Detailed Redox Example with Oxidation Numbers

• Chemical Reaction Example:

  • 3CuCl₂ + 2Al → 3Cu + 2AlCl₃

• Identify Oxidation States:

  • Copper (Cu) oxidation states:

  • Cu from +2 to 0 (it is reduced).

  • Aluminum (Al) oxidation states:

  • Al from 0 to +3 (it is oxidized).

  • Chlorine (Cl) remains unchanged (it does nothing).

Another Redox Reaction

• Chemical Reaction:

  • Mg⁰ + Cu²⁺ → Mg²⁺ + Cu⁰

• Roles of Elements:

  • Magnesium (Mg) is oxidized (loses electrons).

  • Copper ion (Cu²⁺) is reduced (gains electrons).

• Oxidation and Reduction Representation:

  • Oxidation Reaction:

  • Mg → Mg²⁺ + 2e⁻

  • Reduction Reaction:

  • Cu²⁺ + 2e⁻ → Cu

Balancing Redox Equations

• Process of Balancing:

  • Combine the half-reactions to write the overall balanced redox reaction.

• Example Balancing Step:

  • Ensure electrons are equal on both sides.

  • For instance, balance Silver by multiplying by 2:

    • 2Ag⁺ + 2e⁻ → 2Ag

  • Final Combined Reaction:

  • Zn + 2Ag⁺ → Zn²⁺ + 2Ag

Concept Tests

• Testing Oxidation and Reduction:

  • Question: What is oxidation?

  • Answer:

    • Oxidation is the loss of electrons represented by the reaction:

    • X → X⁺ + e⁻

  • Question: What is reduction?

  • Answer:

    • Reduction is the gain of electrons represented by the reaction:

    • X + e⁻ → X⁻

• Redox Reactions Examples:

  • Why is 2Na + Cl₂ → 2NaCl a redox reaction?

  • Both involve the transfer of electrons.

  • Question: Is it possible to oxidize a material without reducing something else?**

  • Answer:

    • No, the loss of electrons from one element must be gained by another element, maintaining charge balance.