Reaction of Aq ions

• What is the reaction that occurs when [M(H2O)6]2+ reacts with H2O?

  [M(H2O)5(OH)]+ + H3O+
• What are the definitions of Lewis acids and bases?

  • Lewis acid: electron pair acceptor
  • Lewis base: electron pair donor
• In the formation of complex ions, which species acts as the Lewis base?

  The ligand acts as the Lewis base by donating a pair of electrons.
• What are metal aqua ions formed in aqueous solution?

  [M(H2O)6]2+ and [M(H2O)6]3+
• Which metal ions correspond to the colors green and blue in [M(H2O)6]2+?

  Fe (green) and Cu (blue)
• What color does Fe(III) appear in solution due to hydrolysis reactions?

  Yellow/brown
• Why is the acidity of [M(H2O)6]3+ greater than that of [M(H2O)6]2+?

  Because the 3+ metal ions have higher charge density and greater polarising power.
• How does polarising power affect the O-H bond in metal aqua ions?

  Greater polarising power weakens the O-H bond, making it break more easily and releasing H+ ions.
• What happens when limited amounts of OH- and NH3 react with metal aqua ions?

  They form the same hydroxide precipitates through deprotonation acid-base reactions.
• What are the precipitates formed with Cu, Fe(II), and Fe(III) when reacting with limited OH- or NH3?


  • M(OH)2(H2O)4: Cu blue ppt, Fe(II) green ppt
  • M(OH)3(H2O)3: Fe(III) brown ppt, Al white ppt
• Write the equation for the reaction of [Cu(H2O)6]2+ with OH-.


  [Cu(H2O)6]2+ + 2OH- → Cu(H2O)4(OH)2 (s) + 2H2O (l)
• Write the equation for the reaction of [Al(H2O)6]3+ with OH-.


  [Al(H2O)6]3+ + 3OH- → Al(H2O)3(OH)3 (s) + 3H2O (l)
• Write the equation for the reaction of [Fe(H2O)6]2+ with NH3.


  [Fe(H2O)6]2+ + 2NH3 → Fe(H2O)4(OH)2 (s) + 2NH4+ (aq)
• Write the equation for the reaction of [Fe(H2O)6]3+ with NH3.


  [Fe(H2O)6]3+ + 3NH3 → Fe(H2O)3(OH)3 (s) + 3NH4+ (aq)
• How does the process of deprotonation occur in metal aqua ions?

  • It can happen stepwise, removing one proton at a time.
  • Example: [Al(H2O)6]3+ + OH- → [Al(H2O)5(OH)]2+ + H2O
• What happens when aluminum hydroxide reacts with excess NaOH?

  It dissolves to form [Al(OH)4]- (aq), a colorless solution.
• Write the equation for the reaction of Al(OH)3 with OH-.

  Al(H2O)3(OH)3 (s) + OH- → [Al(OH)4]- (aq) + 3H2O (l)
• Write the equation for the reaction of Al(OH)3 with H+.

  Al(H2O)3(OH)3 (s) + 3H+ → [Al(H2O)6]3+ (aq)
• What occurs when excess NH3 is added to Cu precipitate?

  A ligand substitution reaction occurs, forming a deep blue solution.
• Write the equation for the reaction of Cu(OH)2 with NH3.

  Cu(OH)2(H2O)4(s) + 4NH3 → [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH- (aq)
• How do NH3 and OH- ions act in the reactions with metal aqua ions?

  • They act as Bronsted-Lowry bases accepting a proton.
  • NH3 acts as a Lewis base donating an electron pair.
• How do 2+ ions react with carbonate solutions compared to 3+ ions?

  2+ ions form MCO3 precipitates, while 3+ ions form M(OH)3 precipitates and evolve CO2 gas.
• What color precipitate is formed when Cu2+ reacts with carbonate solution?

  Blue/green precipitate (CuCO3)
• What color precipitate is formed when Fe(II) reacts with carbonate solution?

  Green precipitate (FeCO3)
• What is the result of the reaction of 3+ ions with carbonate solutions?

  They form M(OH)3 precipitates and evolve CO2 gas.
• Why do 3+ ions not form M2(CO3)3 with carbonate solutions?

  Because of the greater polarising power of the 3+ ion due to its higher charge density.
• Write the equation for the reaction of Fe2+ with CO3 2-.

  Fe2+ (aq) + CO3 2- (aq) → FeCO3 (s)
• Write the equation for the reaction of 2[Fe(H2O)6]3+ with 3CO3 2-.


  2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) → 2Fe(OH)3(H2O)3(s) + 3CO2 + 3H2O(l)
• Write the equation for the reaction of 2[Al(H2O)6]3+ with 3CO3 2-.


  2[Al(H2O)6]3+ (aq) + 3CO3 2- (aq) → 2Al(OH)3(H2O)3(s) + 3CO2 + 3H2O(l)
• Write the equation for the reaction of [Cu(H2O)6]2+ with CO3 2-.


  [Cu(H2O)6]2+ + CO3 2- → CuCO3 + 6H2O
• Write the equation for the reaction of [Fe(H2O)6]2+ with CO3 2-.

  [Fe(H2O)6]2+ + CO3 2- → FeCO3 + 6H2O
• What are the colors of the solutions formed by [M(H2O)6]2+ and [M(H2O)6]3+ ions?

  • [Cu(H2O)6]2+: blue solution
  • [Fe(H2O)6]2+: green solution
  • [Al(H2O)6]3+: colorless solution
  • [Fe(H2O)6]3+: yellow solution
• What are the precipitates formed by M(OH)2 and M(OH)3?

  • M(OH)2(H2O)4: Cu(OH)2 (blue ppt), Fe(OH)2 (green ppt)
  • M(OH)3(H2O)3: Fe(OH)3 (brown ppt), Al(OH)3 (white ppt)
• What are the products of the reactions of metal aqua ions with carbonate solutions?

  • 2+ ions: MCO3 precipitate (Cu blue/green, Fe(II) green)
  • 3+ ions: M(OH)3 precipitate and CO2 gas evolved
• What is the summary of reactions involving 2+ and 3+ ions?

  • 2+ ions: form MCO3 precipitates with carbonate solutions.
  • 3+ ions: form M(OH)3 precipitates and evolve CO2 gas with carbonate solutions.