Lecture Notes: Reactions of Metal Ions in Aqueous Solution

Overview

• Focus on AQA A Level Chemistry
• Topics: Color change, observations, and equations for reactions of metal ions with bases (OH⁻, NH₃, and carbonate)
• Two oxidation states of metal ions: 2+ and 3+
  • 2+ ions: Iron (Fe²⁺) and Copper (Cu²⁺)
  • 3+ ions: Aluminum (Al³⁺) and Iron (Fe³⁺)
• Hexa Aqua complexes and their solutions

Starting Colors of Hexa Aqua Complexes

• Copper (Cu²⁺): Blue solution
• Iron (Fe²⁺): Green solution
• Iron (Fe³⁺): Purple or Violet solution
• Aluminum (Al³⁺): Colorless solution

Reactions with Hydroxide and Ammonia

• Reaction with hydroxide (OH⁻):
  • Form precipitates
  • Cu²⁺: Blue precipitate
  • Fe²⁺: Green precipitate
  • Fe³⁺: Purple to Brown precipitate
  • Al³⁺: White precipitate
• Reaction with ammonia (NH₃):
  • Similar equations to hydroxide
  • Forms ammonium ion (NH₄⁺)
  • Precipitates and their colors remain the same
  • Reaction type: Bronsted-Lowry acid-base (deprotonation)

Excess Hydroxide or Ammonia

• Excess Hydroxide (OH⁻):

  • Al³⁺: Dissolves white precipitate to form colorless solution
  • Complex: Al(OH)₄⁻
  • Amphoteric nature (reacts with both acids and bases)

• Excess Ammonia (NH₃):

  • Cu²⁺: Blue precipitate dissolves to deep blue solution
  • Incomplete ligand substitution: Cu(NH₃)₄(H₂O)₂²⁺ complex
  • Ammonia acts as a Lewis base

Reactions with Carbonates

• 2+ Ions:

  • Reaction forms solid metal carbonates and water
  • Cu²⁺: Blue-green precipitate
  • Fe²⁺: Green precipitate

• 3+ Ions:

  • Formation of precipitates and effervescence due to CO₂ gas
  • Fe³⁺: Brown precipitate
  • Al³⁺: White precipitate

Important Concepts

• Precipitation reactions
• Amphoteric behavior of Al(OH)₄⁻
• Effervescence in reactions with 3+ ions

Practice Questions

1. Observation with Al³⁺ complex reacting with NaOH: Formation of white precipitate
2. Equation for Fe³⁺ complex with carbonate:
   • 2[Fe(H₂O)₆]³⁺ + 3CO₃²⁻ → 2Fe(OH)₃(s) + 3CO₂(g) + 3H₂O(l)
3. Color change and equation for Cu²⁺ with excess NH₃:
   • Equation: Cu(OH)₂(s) + 4NH₃ → [Cu(NH₃)₄(H₂O)₂]²⁺ + 2OH⁻
   • Observation: Blue precipitate to deep blue solution

Tips for Exams

• Memorize the starting colors and precipitate colors
• Understand the differences in reactions with excess reagents
• Be aware of specific terms like "amphoteric" and "effervescence"

---

End of Lecture

• Revise the color changes and equations.
• Practice with the provided questions.
• Like and subscribe for more educational content.