Reactions of Ions in Aqueous Solution

• Equation for the reaction of iron with oxygen and water vapour to form iron (III) hydroxide

  Explain why this type of corrosion is not seen on aluminium structures that have been exposed to the environment

  4Fe(s) + 6H2O(g) + 3O2(g) ---> 4Fe(OH)3(s)

  Aluminium forms an oxide coat, this coat prevents further reaction
• What is the final species produced when an excess of aqueous ammonia is added to aqueous aluminium chloride?

  [Al(OH)3(H2O)3]
• Which compound gives a colourless solution when an excess of dilute aqueous ammonia is added?

  AgCl
• Deduce an ionic equation for the reaction of iron(II) ions with manganate (VII) ions

  5Fe2+ + MnO4- + 8H+ ---> Mn2+ + 5Fe3+ + 4H2O
• Hexaaquairon(III) ions react with an excess of hydrochloric acid in a ligand substitution reaction - Write an equation for this

  Explain why the initial and final iron(III) complexes in the equation have different shapes

  [Fe(H2O)6]3+ + 4Cl- ---> FeCl4- + 6H2O

  Cl- is a bigger ligand so only 4Cl- can fit around the metal
• Reactions with NaOH

  Iron 2+: [Fe(H2O)6]2+ +2OH- --->[Fe(H2O)4(OH)2] + 2H2O

  Ppt is green

  Copper: [Cu(H2O)6]2+ + 2OH- ---> [Cu(H2O)4(OH)2] + 2H2O

  Ppt is blue

  Iron 3+: [Fe(H2O)6]3+ + 3OH- ---> [Fe(H2O)3(OH)3] + 3H2O

  Ppt is purple

  Aluminium: [Al(H2O)6]3+ +3OH- ---> [Al(H2O)3(OH)3 + 3H2O

  Ppt is white
• Amphoteric Salts

  Aluminium salt can act as an acid or base meaning it is amphoteric - if sodium hydroxide is added in excess, the salt acts as an acid and is hydrolysed further

  E.g. [Al(H2O)3(OH)3] (white ppt) + H3O+
• Reactions with NH3

  Iron: [Fe(H2O)6]2+ +2NH3 ---> [Fe(H2O)4(OH)2] + 2NH4+

  Ppt is green

  Copper: [Cu(H2O)6]2+ +2NH3 ---> [Cu(H2O)4(OH)2] + 2NH4+

  Ppt is blue

  Iron 3+: [Fe(H2O)6]3+ + 3NH3 ---> [Fe(H2O)3(OH)3] + 3NH4+

  ppt is purple

  Aluminium: [Al(H2O)6]3+ + 3NH3 ---> [Al(H2O)3(OH)3] + 3NH4+

  When ammonia is added in excess to these precipitates, the copper(II) salt undergoes ligand substitution to form a deep blue solution

  E.g. [Cu(H2O)4(OH)2] + 4NH3 ---> [Cu(H2O)2(NH3)4]2+ +2H2O + 2OH-
• Reactions with Na2CO3

  Solutions of these metal 2+ ions react with sodium carbonate as acids, forming insoluble carbonates and water

  Iron: [Fe(H2O)6]2+ + CO32- ---> FeCO3 + 6H2O

  Ppt is green

  Copper: [Cu(H2O)6]2+ + CO32- ---> CuCO3 + 6H2O

  Ppt is blue

  Solutions of metal 3+ ions act as stronger acids - react with sodium carbonate to form a salt, water and carbon dioxide

  Iron: 2[Fe(H2O)6]3+ + 3CO32- ---> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2

  Aluminium: 2[Al(H2O)6]3+ + 3CO32- ---> 2[Al(H2O)3(OH)3] + 3H2O + 3CO2
• Reactions with Cl- ions

  All metal aqua ions undergo ligand substitution reactions to form tetrahedral ions with four Cl- ligands - react with conc hydrochloric acid

  Iron: [Fe(H2O)6]2+ + 4Cl- ---> [FeCl4]2- + 6H2O

  Copper: [Cu(H2O)6]2+ + 4Cl- ---> [CuCl4]2- + 6H2O (Solution is yellow-green)

  Iron 3+: [Fe(H2O)6]3+ + 4Cl- ---> [FeCl4]- + 6H2O

  Aluminium: [Al(H2O)6]3+ + 4Cl- ---> [AlCl4]- + 6H2O
• What forms when a solution of sodium carbonate is added to a solution of gallium (III) nitrate?

  A white precipitate of gallium (III) hydroxide and bubbles of carbon dioxide
• Which compound gives a colourless solution when an excess of dilute aqueous ammonia is added?

  AgCl
• What is the final species produced when an excess of aqueous ammonia is added to aqueous aluminium chloride?

  [Al(OH)3(H2O)3]