Aqueous ions

• Transition metal salts dissolve in water to form aqua ion complexes with water molecules ligands.
• In [Fe(H2O6] 3+ and other complexes, the metal ion is strongly polarising so it weakens the O-H and causes a H+ ion to be released
• The reaction is hydrolysis because water molecules are being split
• Example equation:

  • [M(H2O)6] 3+ + H2O ⇌ [M(H2O)5 OH] 2+ + H3O+ (this is a H+ ion)
  • Which would make the solution acidic
• Smaller and greater charge metal ions exert a greater polarising effect on water ligands so that more O-H bonds break which releases H+ ions which causes a more acidic solution to be produced
• Hydrolysis reaction can also happen when OH- is added as it shifts equation to the right due to removing the H+ from the metal complex

  e.g. [M(H2O)6] 2+ (aq) + OH- ---> [M(H2O)5 OH]+(s) + H2O(l)
• Hydrolysis reaction continue to occur until overall charge on transition metal complex is 0
• Hydrolysis reaction can also happen with NH3 to form ammonium instead of water.

  E.g. [M(H2O)6] 2+ (aq) + NH3 ---> [M(H2O)5 OH]+ (s) + NH4+
• For all hydrolysis reactions, the product is an uncharged, insoluble metal hydroxide that forms a precipitate
• Aqueous ions also react with carbonate ions

  • As sodium carbonate act as a base with M3+ aqua ions to produce a hydrated metal hydroxide due to the strong charge it makes it act as an acid
  • Bubbles would form
  • This is a deprotonation reaction
  • Reaction: 2[Fe(H2O)6] 3+ (aq) + 3CO3 2-(aq) --> 2[Fe(H2O)3(OH)3](s) +3CO2(g) + 3H2O(l)
• However, adding sodium carbonate to M2+ ions produce an insoluble metal carbonate due to the weaker charge so its less acidic

  • No bubbles forms
  • This is a ligand substitution reaction
  • E.g. [Cu(H2O)6]2+ (aq) + CO3 2-(aq) ---> CuCO3 (s) + 6H2O(l)
• The colour of [Fe(H2O)6]2+ is green
• The colour of [Cu(H2O)6]2+ solution is blue
• The colour of [Fe(H2O)6]3+ is yellow
• The colour of [Al(H2O)6]3+ solution is colourless
• The colour of [Co(H2O)6]2+ is pink
• Adding OH- (aq) to aqueous solution

  For [Fe(H2O)6]2+

  • A green precipitate forms
  • Equation is [Fe(H2O)6]2+ (aq) +2OH- ---> [Fe(H2O)4 (OH)2](s) +2H2O

  For [Cu(H2O)6]2+

  • A blue precipitate forms
  • Equation is [Cu(H2O)6]2+ (aq) + 2OH- ----> [Cu(H2O)4 (OH)2](s) +2H2O

  For [Fe(H2O)6]3+

  • A brown precipitate forms
  • Equation is [Fe(H2O)6]3+ (aq) + 3OH- ---> [Fe(H2O)3 (OH)3](s) +3H2O
• Adding OH- (aq) to aqueous solution

  For [Al(H2O)6]3+

  • A white precipitate forms
  • Equation is [Al(H2O)6]3+ (aq) + 3OH- ---> [Al(H2O)3 (OH)3](s) +3H2O

  For [Co(H2O)6] 2+

  • A blue precipitate forms
  • Equation is [Co(H2O)6]2+ (aq) + 2OH- ---> [Co(H2O)4 (OH)2](s) +2H2O
• Adding excess of OH- to aqueous solution only changes the colour of [Al(H2O)6]3+ solution from white precipitate to colourless. The formula for is [Al(H2O)6] 3+ + 4OH– → [Al(OH)4]– + 6H2O
• Adding NH3 (aq) to aqueous solution

  For [Fe(H2O)6]2+

  • A green precipitate forms which darkens and turn brown in air
  • Equation is [Fe(H2O)6]2+(aq) + 2NH3 --> [Fe(H2O)4 (OH)2](s) + 2NH4+

  For [Cu(H2O)6]2+

  • A blue precipitate forms
  • Equation is [Cu(H2O)6]2+(aq) + 2NH3 --> [Cu(H2O)4 (OH)2](s) + 2NH4+

  For [Fe(H2O)6]3+

  • A brown precipitate forms
  • Equation is [Fe(H2O)6]3+(aq) + 3NH3 --> [Fe(H2O)3 (OH)3](s) + 3NH4+
• Adding NH3 (aq) to aqueous solutions

  For [Al(H2O)6]3+

  • A white precipitate forms
  • [Al(H2O)6]3+(aq) + 3NH3 --> [Al(H2O)3 (OH)3](s) + 3NH4+
• Adding excess NH3 (aq) to the precipitate

  For [Cu(H2O)6]2+

  • A deep blue solution forms
  • [Cu(H2O)4(OH)2] + 4NH3 ---> [Cu(NH3)4(H2O)2] 2+ + 2H2O + 2OH-

  For [Co(H2O)6]2+

  • A pale brown solution forms
  • [Co(H2O)4(OH)2] + 6NH3 ---> [Co(NH3)6]2+ + 4H2O +2OH-
• Adding carbonate ions to aqueous solution

  For [Fe(H2O)6]2+

  • A green precipitate forms
  • [Fe(H2O)6]2+ + CO3 2- ---> FeCO3 + 6H2O

  For [Cu(H2O)6]2+

  • A blue green precipitate forms
  • [Cu(H2O)6]2+ + CO3 2- ----> CuCO3 + 6H2O

  For [Co(H2O)6]2+

  • A purple precipitate forms
  • [Co(H2O)6]2+ + CO3 2- ----> CoCO3 + 6H2O
• Adding carbonate ions to aqueous solution

  For [Fe(H2O)]3+

  • A brown precipitate forms and effervescence
  • 2[Fe(H2O)]3+ + 3 CO3 2- ---> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2

  For [Al(H2O)]3+

  • White precipitate forms and effervescence
  • 2[Al(H2O)]3+ + 3 CO3 2- ---> 2[Al(H2O)3(OH)3] + 3H2O + 3CO2
• Adding concentrated HCl

  For [Cu(H2O)6]2+

  • Colour chance to green from blue
  • [Cu(H2O)6]2+ + 4Cl- ----> [CuCl4]2- + 6H2O

  For [Co(H2O)6]2+

  • Colour change to dark blue but looks pink if there's some [Co(H2O)6] left
  • [Co(H2O)6]2+ + 4Cl- ----> [CoCl4]2- + 6H2O
• To reduce [Fe(H2O)6]3+ to [Fe(H2O)6]2+ you add excess of Zn in sulphuric acid