Class 11 Chemistry Redox Reactions Notes

7.1 Classical Idea of Redox Reactions – Oxidation and Reduction

• Oxidation: Process involving loss of electrons or addition of oxygen.
• Reduction: Process involving gain of electrons or removal of oxygen.
• Classical examples:
  • $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$Zn+Cu2+→Zn2++Cu
    • Zn → Zn²⁺ + 2e⁻ (Oxidation)
    • Cu²⁺ + 2e⁻ → Cu (Reduction)
• Redox reaction: Combination of oxidation and reduction.

7.2 Redox Reactions in Terms of Electron Transfer

• Electron transfer view:
  • Oxidation = loss of electrons
  • Reduction = gain of electrons
• Example:

$$Fe^{2+} + Ce^{4+} \rightarrow Fe^{3+} + Ce^{3+}$$Fe2++Ce4+→Fe3++Ce3+

• Half-reactions:
  • Oxidation: $Fe^{2+} \rightarrow Fe^{3+} + e^-$Fe2+→Fe3++e−
  • Reduction: $Ce^{4+} + e^- \rightarrow Ce^{3+}$Ce4++e−→Ce3+

7.3 Oxidation Number

• Definition: Charge assigned to an atom in a molecule or ion according to a set of rules.
• Rules for assigning oxidation numbers:
  1. Element in standard state = 0.
  2. Monatomic ion = charge on the ion.
  3. Oxygen usually = -2 (except in peroxides).
  4. Hydrogen usually = +1 (except in hydrides).
  5. Sum of oxidation numbers in molecule = overall charge.
• Use: Identify oxidation and reduction in reactions.

7.4 Redox Reactions and Electrode Processes

• Electrochemical perspective:
  • Oxidation occurs at anode.
  • Reduction occurs at cathode.
• Electrochemical cells: Convert chemical energy to electrical energy via redox reactions.
• Examples: Galvanic cells, electrolytic cells.
• Applications: Batteries, corrosion prevention, metal extraction.

Key Points to Remember

• Redox reactions involve simultaneous oxidation and reduction.
• Electron transfer is central to understanding redox chemistry.
• Oxidation number rules help track changes in electrons.
• Redox reactions are the basis of electrochemical processes and industrial applications.