3.2.6: Reactions of ions in aqueous solution

• Aqueous ion of Iron (II):

  • [Fe(H2O)6]2+ (aq.)
  • Observation: GREEN SOLUTION
• Action of NaOH on Fe (II):

  • Fe(H2O)4(OH)2 (s.)
  • Observation: GREEN PRECIPITATE -> BROWN standing in air
• Action of EXCESS NaOH (aq.) on Fe (II):

  • No further change
• Action of NH3 (aq.) on Fe (II):

  • Fe(H2O)4(OH)2 (s.)
  • Observation: GREEN PRECIPITATE goes BROWN standing in air
• Action of EXCESS NH3 (aq.) on Fe (II):

  • No further change
• Action of Na2CO3 (aq.) on Fe (II):

  • FeCO3 (s.)
  • Observation: GREEN PRECIPITATE
• Aqueous ion of Cu (II):

  • [Cu(H2O)6]2+ (aq.)
  • Observation: BLUE SOLUTION
• Action of NaOH on Cu (II):

  • Cu(H2O)4(OH)2 (s.)
  • Observation: BLUE PRECIPITATE
• Action of EXCESS NaOH (aq.) on Cu (II)

  • No further change
• Action of NH3 (aq.) on Cu (II):

  • Cu(H2O)4(OH)2 (s.)
  • Observation: BLUE PRECIPITATE
• Action of EXCESS NH3 (aq.) on Cu (II):

  • [Cu(H2O)2(NH3)4]2+
  • Observation: DEEP-BLUE SOLUTION
• Action of Na2CO3 (aq.) on Cu (II):

  • CuCO3 (s.)
  • Observation: BLUE-GREEN PRECIPITATE
• Aqueous ion of Fe (III):

  • [Fe(H2O)6]3+ (aq.)
  • Observation: PURPLE solution (may look YELLOW-BROWN due to [Fe(H2O)5OH]2+)
• Action of NaOH (aq.) on Fe (III):

  • Fe(H2O)3(OH)3 (s.)
  • Observation: BROWN PRECIPITATE (may look ORANGE-BROWN)
• Action of excess NaOH (aq.) on Fe (III):

  • No further change
• Action of NH3 (aq.) on Fe (III):

  • Fe(H2O)3(OH)3 (s.)
  • Observation: BROWN PRECIPITATE (may look ORANGE-BROWN)
• Action of EXCESS NH3 (aq.) on Fe (III):

  • No further change
• Action of Na2CO3 (aq.) on Fe (III):

  • Fe(H2O)3(OH)3 (s.)
  • Observation: BROWN PRECIPITATE (may look ORANGE-BROWN) and CO2 gas effervescence
• Aqueous ion of Al (III):

  • [Al(H2O)6]3+ (aq.)
  • Observation: COLOURLESS SOLUTION
• Action of NaOH on Al (III):

  • Al(H2O)3(OH)3 (s.)
  • Observation: WHITE PRECIPITATE
• Action of EXCESS NaOH (aq.) on Al (III):

  • [Al(OH)4]- (aq.)
  • OBSERVATION: COLOURLESS SOLUTION
• Action of NH3 (aq.) on Al (III):

  • Al(H2O)3(OH)3 (s.)
  • Observation: WHITE PRECIPITATE
• Action of EXCESS NH3 (aq.) on Al (III):

  • No further change
• Action of Na2CO3 (aq.) on Al (III):

  • Al(H2O)3(OH)3 (s.)
  • Observation: WHITE PRECIPITATE and CO2 gas effervescence
• Acidity of M3+ ions compared to M2+ ions:

  • M3+ ions have a greater charge density (same size ion, but greater charge)
  •  ∴ M3+ ions more polarising than M2+ -> WEAKENS O-H bond
  • H+ more readily released (from H2O ligands),  ∴ decrease in pH / increased acidity