Reactions of aqueous 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
• Why is the ligand considered a Lewis base in complex ion formation?

  Because it donates a pair of electrons in the dative covalent bond
• 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 3+ metal ions have higher charge density and greater polarising power
• How does polarising power affect the O-H bond in metal aqua ions?

  The greater the polarising power, the more strongly it attracts the water molecule, weakening the O-H bond
• What precipitates are formed when limited amounts of OH- and NH3 react with metal aqua ions?

  M(OH)2(H2O)4 and M(OH)3(H2O)3
• What are the colors of the precipitates formed from Cu and Fe with limited OH- and NH3?

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

  [Al(H2O)6]3+ + 3OH- → Al(H2O)3(OH)3 + 3H2O
• What happens to aluminium hydroxide when excess NaOH is added?


  It dissolves to form [Al(OH)4]- (aq), a colorless solution
• Why is aluminium hydroxide classified as amphoteric?

  Because it reacts and dissolves in both acids and bases
• Write the equation for the reaction of Al(OH)3 with OH-.

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

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

  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+ + 2H2O + 2OH-
• How do NH3 and OH- act in the reactions described?

  They act as Bronsted-Lowry bases accepting a proton
• What is the difference in reaction between 2+ and 3+ ions with carbonate solutions?

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

  CuCO3 (s)
• What precipitate is formed when Fe2+ reacts with carbonate solution?

  FeCO3 (s)
• Write the equation for the reaction of 2[Fe(H2O)6]3+ with carbonate solution.


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


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

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

  [Fe(H2O)6]2+ + CO3^2- → FeCO3 + 6H2O
• What are the colors of the solutions formed by different metal aqua 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 metal hydroxides with limited OH- or NH3?

  • Cu(OH)2(H2O)4: blue ppt
  • Fe(OH)2(H2O)4: green ppt
  • Fe(OH)3(H2O)3: brown ppt
  • Al(OH)3(H2O)3: white ppt
• What are the precipitates formed by carbonate reactions with metal ions?

  • CuCO3: blue ppt
  • FeCO3: green ppt
  • Al(OH)3(H2O)3: white ppt + bubbles of CO2
  • Fe(OH)3(H2O)3: brown ppt + bubbles of CO2
• What is the summary of reactions for 2+ and 3+ ions with hydroxide and carbonate solutions?

  • 2+ ions form MCO3 precipitates.
  • 3+ ions form M(OH)3 precipitates and evolve CO2 gas.
• What is the summary of the colors and precipitates formed by metal aqua ions?

  • [M(H2O)6]2+: blue or green solutions
  • [M(H2O)6]3+: colorless or yellow solutions
  • Precipitates: Cu(OH)2, Fe(OH)2, Al(OH)3, Fe(OH)3
• How do the reactions of 2+ and 3+ ions with carbonate solutions differ?

  • 2+ ions form MCO3 precipitates.
  • 3+ ions form M(OH)3 precipitates and release CO2 gas.