Lecture Notes: Oxidation and Reduction Reactions

Presenter: Robert Smith, Academic Assistance at New River Community College

Overview

• Focus on assigning oxidation states (oxidation numbers) to elements in compounds.
• Introduction to general rules for assigning oxidation states.

Key Rules for Assigning Oxidation States

• Group 1 Elements: Oxidation state of +1.
• Group 2 Elements: Oxidation state of +2.
• Hydrogen:
  • +1 when attached to a non-metal.
  • -1 when attached to a metal.
• Oxygen: Usually -2.
  • Exceptions:
    • Peroxide ion: -1
    • Superoxide ion: -1/2 (rarely seen)

Example Calculations

Example 1: Na₂O

• Compound: Na₂O
• Oxygen: -2 (not in peroxide/superoxide)
• Condition: Sum of oxidation states = 0 (neutral compound)
• Sodium: Must balance -2 from Oxygen, thus total for 2 Na = +2
  • Oxidation state of each Na = +1
• Equation: 2(Na) + O = 0

Example 2: HClO₃

• Compound: HClO₃
• Hydrogen: +1 (attached to non-metal)
• Oxygen: -2 each, total -6 (3 Oxygens)
• Equation: 1 (H) + x (Cl) - 6 (O) = 0
  • Solving for x: x = +5
• Chlorine: +5 oxidation state

Example 3: HPO₄

• Compound: HPO₄
• Hydrogen: +1
• Oxygen: -2 each, total -8 (4 Oxygens)
• Condition: Sum of oxidation states = -2 (charge of ion)
• Equation: 1 (H) + x (P) - 8 (O) = -2
  • Solving for x: x = +5
• Phosphorus: +5 oxidation state

Key Points on Oxidation State Assignment

• Hydrogen and Oxygen are key indicators:
  • Hydrogen: +1 with non-metals, -1 with metals.
  • Oxygen: Generally -2, except for peroxide/superoxide.
• Group 1 & 2 Elements: Same oxidation state as their charge.

Additional Information

• Further Reading: More rules in PowerPoint presentation for this chapter.