3.2.6 Reactions of ions in aqueous solution

• Hydrated metal ions exist as hexaaqua complexes
• What is the colour of [Fe(H2O)6]2+? Green
• What is the colour of [Cu(H2O)6]2+? Blue
• What is the colour of [Al(H2O)6]2+? Colourless
• What is the colour of [Fe(H2O)6]3+? Purple
• Hexa-aqua ions can act as acids because

  • the charge on the cation attracts electrons.
  • Bonds in the water ligand are weakened
  • So H+ can be remove
• M2+ acids are weak
• What type of reactions do metal-aqua ions undergo when reacting with water? hydrolysis
• What colour is Fe(OH)2? Green
• What colour is Cu(OH)2? Blue
• What colour is Al(OH)3?" White
• What colour is Fe(OH)3?" Brown
• When M2+ ions react with carbonate, insoluble carbonates form
• What colour is FeCO3? Green
• What colour is CuCO3? Blue-green
• Observations for Iron (III) reacting with carbonate? 

  • Brown precipitate
  • and effervescence
• Observations for Aluminium (III) reacting with carbonate:

  • White precipitate and effervescence
• Colours of vanadium ions:

  • +5 - yellow
  • +4 - blue
  • +3 - green
  • +2 - violet
• 3+ ions are much more acidic than 2+ ions
• 3+ ions are smaller and more highly charged than 2+ ions, so have a higher charge density. They attract the electrons from the oxygen of the ligands much more strongly
• Write an equation for the hydrolysis of a 3+ ion to release a proton:

  
  

  [Fe(H2O)6 ] 3+ (aq) ⇌ [Fe(H2O)5 (OH)]2+ (aq) + H+ (aq)
• What kind of acid is the complex ion acting as? [Fe(H2O)6 ] 3+ (aq) ⇌ [Fe(H2O)5 (OH)]2+ (aq) + H+ (aq)

  
  

  Answer:

  Bronsted-Lowry
• Lewis acid definition: Electron pair acceptor
• Define a Lewis base: Electron pair donor