Topic 10 - Redox Reactions (1)

Topic 10 - Redox Reactions

• Prepared by Mrs. Haneen Kheir

• Pages: 203 - 218

Introduction to Redox Reactions

• Definition of Oxidation and Reduction

  • Oxidation: A substance is oxidized if it gains oxygen.

  • Reduction: A substance is reduced if it loses oxygen.

  • Redox reactions involve both oxidation and reduction as they occur simultaneously; one substance loses oxygen while another gains it.

Oxidation and Reduction Concepts

• Alternative Definitions:

  • Oxidation can also be defined as the loss of electrons.

  • Reduction is defined as the gain of electrons.

• Spectator Ions:

  • Ions that do not change during the reaction (e.g., O2- ions can be removed from the equation).

• Ionic Equation:

  • Shows only the significant ions and atoms involved in the reaction, excluding spectator ions.

Understanding Redox Agents

• Oxidizing Agent:

  • A substance that oxidizes another by providing oxygen or accepting electrons; it undergoes reduction itself.

• Reducing Agent:

  • A substance that reduces another by donating electrons; it undergoes oxidation itself.

Definitions Summary

• Oxidation: Loss of electrons and gain of oxygen.

• Reduction: Gain of electrons and loss of oxygen.

• Redox Reaction: Occurs when oxidation and reduction happen simultaneously.

• Oxidizing Agent: Gains electrons and loses oxygen.

• Reducing Agent: Loses electrons and gains oxygen.

Application of Redox Concepts in Equations

• Determining Oxidized and Reduced Substances:

  • Key examples given with explanations based on oxygen or electron transfer:

    • Example a: Zn(s) + CuO(s) → ZnO(s) + Cu(s) (Zn oxidized; gain of oxygen)

    • Example b: Fe2O3(s) + 3C(s) → 2Fe(s) + 3CO(g) (Fe reduced; loss of oxygen)

    • Example c: Mg(s) + Zn2+(aq) → Mg2+(aq) + Zn(s) (Mg oxidized; loss of electrons)

    • Example d: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) (Cu reduced; gain of electrons)

Recap Activities

• Engage with interactive games to reinforce understanding of oxidation and reduction concepts.

Key Points on Oxidizing and Reducing Agents

• Examples of Reducing Agents:

  • Carbon in the reaction: C + O2 → CO2 (reduces oxygen; oxidized to CO2)

  • Sodium: 2Na + Cl2 → 2NaCl (reduces chlorine; oxidized to Na+)

  • Iron(III) oxide: Fe2O3 + 2Al → Al2O3 + 2Fe (oxidizes Al; reduced to Fe)

Oxidation Numbers

• Definition: The charge assigned to an atom in a compound indicating electron transfer.

• Rules for Determining Oxidation Numbers:

  1. Elements alone have an oxidation number of zero.

  2. For simple ions, the oxidation number equals the ion's charge.

  3. In a neutral compound, the sum of oxidation states = 0.

  4. In polyatomic ions, the sum equals the ion's charge.

Special Cases of Oxidation Numbers

• Oxidation states vary for different elements especially in variable states.

• Fluorine is always -1 in compounds.

• Oxidation numbers are also indicated in compound names, e.g., iron(III) hydroxide.

Redox Reactions and Oxidation States

• Displacement Reactions Examples:

  • Metals react with acids (e.g., Mg + HCl → H2 + Mg2+; H+ reduced, Mg oxidized).

  • Zinc and Copper example illustrates loss and gain of electrons clearly.

Distinguishing Oxidation and Reduction in Reactions

• Recognize when certain reactants are oxidized or reduced by monitoring the changes in oxidation state during reactions such as Cu and AgNO3 or Ca and FeCl3.

Quiz Questions on Redox Concepts

• Questions assess comprehension and identification of oxidation/reduction processes, oxidation states, and defining key terms related to redox reactions.