Aqueous ions

• Copper (II) with ammonia

  [Cu(H2O)6]2+ + 2NH3 ⇌ [Cu(H2O)4(OH)2] (s) + 2NH4+

  
  

  Blue precipitate

  Hexaaquacopper is a blue solution

  Hydrolysis
• What type of reactions can metal ions qua can undergo?

  Ligand substitution or a hydrolysis reaction
• What does it depend on for one of these reactions to happen?

  The bonds in the complex that are broken
• Overview of Ligand substitution reaction

  If the co-ordinate bond between a water ligand and the central metal ion breaks, the water ligand can be replaced by another ligand.
• Overview of hydrolysis reaction

  If the O-H in a water ligand breaks, a hydrogen ion is made
• What products are made when aluminium chloride (AlCl3) dissolves in water?

  [Al(H2O)6]3+ and 3Cl-

  
  

  A colourless hexaaquaaluminium(III)
• Why is the solution formed acidic, with a pH of 3?

  [Al(H2O)6]3+ reacts with water molecule to make H3O+

  
  

  A hydrolysis reaction occurs in a water molecule of the complex
• [Al(H2O)6]3+ + H2O ⇌ [Al(H2O)5(OH)]2+ + H3O+

  [Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)]2+ + H+

  
  

  This reaction is ----------

  The position of the equilibrium lies to the ----, which is why the solution is ------

  ------

  Type of reaction is -------- --------

  Metal hexaaqua ions where the central metal ion has a -- or -- undergo ---------- reactions

  a) reversible

  b) left

  c) weakly acidic

  d) acidity reaction

  e) +2

  f) +3

  g) hydrolysis
• What does iron(III) compounds make when dissolved in water?

  Produce a PURPLE hexaaquairon (III)

  
  

  FeCl3 + 6H2O → [Fe(H2O)6]3+ + 3Cl-
• Then, what happens after the iron (III) compounds is dissolved in water?

  [Fe(H2O)6]3+ + H2O ⇌ [Fe(H2O)5(OH)]2+ + H3O+

  [Fe(H2O)6]3+ ⇌ [Fe(H2O)5(OH)]2+ + H+

  
  

  Hydrolysis making WEAKLY ACIDIC SOLUTION
• What does copper(II) compounds make when dissolved in water?

  Produce a BLUE hexaaquacopper (II)

  
  

  CuCl2 + 6H2O → [Cu(H2O)6]2+ + 2Cl-
• Then, what happens after the copper (II) compounds is dissolved in water?

  [Cu(H2O)6]2+ + H2O ⇌ [Cu(H2O)5(OH)]+ + H3O+

  [Cu(H2O)6]2+ ⇌ [Cu(H2O)5(OH)]+ + H+

  
  

  Hydrolysis making a VERY WEAKLY ACIDIC SOLUTION with a pH of 6, as the position of equilibrium lies very far to the left
• What about iron (II) compounds?

  Occurs with green hexaaquairon (II)

  
  

  [Fe(H2O)6]2+ + H2O ⇌ [Fe(H2O)5(OH)]+ + H3O+

  [Fe(H2O)6]2+ ⇌ [Fe(H2O)5(OH)]+ + H+

  
  

  Hydrolysis making a VERY WEAKLY ACIDIC SOLUTION with a pH of 6, as the position of equilibrium lies very far to the left
• Overall, what type of solutions do M3+ hexaaqua ions and M2+ hexaaqua ions form?

  M3+ form weakly acidic solutions

  
  

  M2+ forms very weakly acidic solutions
• How does having a high charge to size ratio affect acidity?

  
  

  High charge to size ratio: The metal ion is highly charged and small in size

  
  

  Like M3+ has a higher charge to size ratio than M2+


  - Has greater polarising power

  - Attract the electron density more strongly from the oxygen in water ligands

  - O-H bond weaker, more easily broken and releasing a H+

  - pH of [M(H2O)6]3+ is lower than [M(H2O)6]2+
• What are the general equations for reactions of complexes with base like sodium hydroxide?

  [M(H2O)6]3+ + 3OH- ⇌ [M(H2O)3(OH)3] (s) + H2O

  
  

  [M(H2O)6]2+ + 2OH- ⇌ [M(H2O)4(OH)2] (s) + H2O
• Copper (II) with sodium hydroxide

  [Cu(H2O)6]2+ + 2OH- ⇌ [Cu(H2O)4(OH)2] (s) + H2O

  
  

  Blue precipitate

  Hexaaquacopper is a blue solution
• Iron (II) with sodium hydroxide


  [Fe(H2O)6]2+ + 2OH- ⇌ [Fe(H2O)4(OH)2] (s) + H2O

  
  

  Green precipitate

  Hexaaquairon is a green solution

  
  

  Iron (II) hydroxide is rapidly oxidised by oxygen in air to iron (III) hydroxide, changing it to orangey-brown colour.
• Aluminium (III) with sodium hydroxide

  [Al(H2O)6]3+ + 3OH- ⇌ [Al(H2O)3(OH)3] (s) + H2O

  
  

  White precipitate

  [Al(H2O)6]3+ is a colourless solution
• Why does aluminium hydroxide forms a white precipitate?

  Not a transition metal, so there is no splitting of the d orbitals, so there is no absorbance of light
• Which metal hydroxides dissolve in excess sodium hydroxide?

  Metal (III) hydroxides

  
  

  [Al(H2O)3(OH)3] (s) + OH- ⇌ [Al(OH)4]- + 3H2O

  
  

  
  

  White precipitate into a colourless solution
• Iron (III) with sodium hydroxide


  [Fe(H2O)6]3+ + 3OH- ⇌ [Fe(H2O)3(OH)3] (s) + H2O

  
  

  Brown precipitate

  [Fe(H2O)6]3+ is a purple solution
• What is an amphoteric hydroxide?

  Something that can be acid or a base based on its conditions
• What happens with [Al(H2O)6]3+, a colourless solution, in

  
  

  a) aqueous sodium hydroxide?

  b) excess sodium hydroxide?

  a) forms a white precipitate of [Al(H2O)3(OH)3]

  b) forms a colourless solution of [Al(OH)4]-
• What does [Al(H2O)3(OH)3] do in excess acid?

  Dissolves to form a colourless solution of [Al(H2O)6]3+

  
  

  So aluminium hydroxide is an amphoteric as it dissolves both in acids and bases
• What are the general equations for reactions of complexes with ammonia?

  [M(H2O)6]3+ + 3NH3 ⇌ [M(H2O)3(OH)3] (s) + 3NH4+

  
  

  [M(H2O)6]2+ + 2NH3 ⇌ [M(H2O)4(OH)2] (s) + 2NH4+
• What happens with copper (II) with excess ammonia?

  A deep blue solution is formed

  
  

  [Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(H2O)2(NH3)4]2+ + 3H2O

  
  

  However, only four of the aqua ligands are substituted by ammonia ligands because this is a distorted octahedral, in which the axial ligand bonds are stronger and shorter, so harder to substitute.
• [Cu(H2O)2(NH3)4]2+


  Shape: (distorted) octahedral

  4 ammonia ligands lie in the same plane

  2 water ligands lie above and below the plane
• Iron (II) with ammonia


  [Fe(H2O)6]2+ + 2NH3 ⇌ [Fe(H2O)4(OH)2] (s) + 2NH4+

  
  

  Green precipitate

  Hexaaquairon is a green solution

  
  

  Iron (II) hydroxide is rapidly oxidised by oxygen in air to iron (III) hydroxide, changing it to orangey-brown colour.
• Aluminium (III) with ammonia

  [Al(H2O)6]3+ + 3NH3 ⇌ [Al(H2O)3(OH)3] (s) + 3NH4+

  
  

  White precipitate

  [Al(H2O)6]3+ is a colourless solution
• Iron (III) with ammonia

  [Fe(H2O)6]3+ + 3NH3 ⇌ [Fe(H2O)3(OH)3] (s) + 3NH4+

  
  

  Brown precipitate

  Hexaaquairon is a purple solution
• What does metal(III) hydroxides do instead of dissolving in excess ammonia?

  A ligand substitution happens where the liands are exchanged for ammonia ligands except for d8 metals
• What is the general equation for reactions of complexes with carbonates?

  [M(H2O)6]2+ + CO3 2- → MCO3 + 6H2O

  2[M(H2O)6]3+ + 3CO3 2- ⇌ 2[M(H2O)3(OH)3] (s) + 3H2O + 3CO2 (effervescence)
• Copper (II) with sodium carbonate


  [Cu(H2O)6]2+ + CO3 2- ⇌ CuCO3 (s) + 6H2O

  
  

  Blue-green precipitate

  Hexaaquacopper is a blue solution
• Iron (II) with sodium carbonate

  [Fe(H2O)6]2+ + CO3 2- ⇌ FeCO3 (s) + 6H2O

  
  

  Green precipitate

  Hexaaquairon is a green solution

  Yellow bit as well due to further oxidation of Fe(II)
• Aluminium (III) with sodium carbonate

  2[Al(H2O)6]3+ + 3CO3 2- ⇌ 2[Al(H2O)3(OH)3] (s) + 3H2O + 3CO2 (effervescence)

  
  

  White precipitate

  [Al(H2O)6]3+ is a colourless solution
• Iron (III) with sodium carbonate

  2[Fe(H2O)6]3+ + 3CO3 2- ⇌ 2[Fe(H2O)3(OH)3] (s) + 3H2O + 3CO2 (effervescence)

  
  

  Brown precipitate

  [Fe(H2O)6]3+ is a purple solution