Summary AQA A-Level Chemistry 2.6 Reactions of Inorganic Compounds in Aqueous Solution

Reactions of Inorganic Compounds in Aqueous Solutions
24.1 The Acid-Base Chemistry of Aqueous Transition Metal Ions:
24.1 the acid-base chemistry of aqueous
- Metal ions become hydrated in water with H2O ligands
around the metal ion transition metal ions
- Metal 3+ ions are more acidic than 2+ ions. This is because 24.2 ligand substitution reactions
they have a greater charge density and so have a higher
polarising power. 24.3 a summary of acid-base and
- As charge density increases the cation has a greater substitution reactions of some metal ions
attraction for water, this pulls the electron pair in the O-H
bond towards the O. This makes the H more acidic.
- Water acts as a Lewis Base and the metal ions act as Lewis bases.
- Some substances can show both acidic and basic properties, these are called amphoteric. Aluminium is an
example of an amphoteric hydroxide.
o Al(H2O)3(OH)3 + 3HCl à Al(H2O)63+ + 3Cl-
o Al(H2O)3(OH)3 + OH- à [Al(OH)4]- + 3H2O
Reactions with Sodium Hydroxide:
- The hydroxide group takes a proton from the water ligand leaving a hydroxide group in the complex and
forming water. This continues until the complex is neutral, it forms a solid and drops out of solution, a
precipitate will form.
- [Fe(H2O)6]2+(aq) + 2OH- à Fe(H2O)4(OH)2(s) + 2H2O(l)
- [Cu(H2O)6]2+(aq) + 2OH- à Cu(H2O)4(OH)2(s) + 2H2O(l)
- [Fe(H2O)6]3+(aq) + 3OH- à Fe(H2O)3(OH)3(s) + 3H2O(l)
- [Al(H2O)6]3+(aq) + 3OH- à Al(H2O)3(OH)3(s) + 2H2O(l)
o If more sodium hydroxide is added in excess aluminium can undergo a further reaction to form
[Al(OH)4]-
o Al(H2O)3(OH)3(s) + OH- à [Al(OH)4]-(aq) + 3H2O(l)
Reactions with Ammonia:
- Reactions with ammonia work in the same was as with sodium hydroxide, precipitates will form and drop
out of solution
- [Fe(H2O)6]2+(aq) + 2NH3(aq)à Fe(H2O)4(OH)2(s) + 2NH4+(aq)
- [Cu(H2O)6]2+(aq) + 2NH3(aq)à Cu(H2O)4(OH)2(s) + 2NH4+(aq)
o If excess is added a further step occurs
o Cu(H2O)4(OH)2(s) + 4NH3(aq) à [Cu(H2O)2(NH3)4]2+(aq)+ 2OH-(aq) + 2H2O(l)
- [Fe(H2O)6]3+(aq) + 3NH3(aq)à Fe(H2O)3(OH)3(s) + 3NH4+(aq)
- [Al(H2O)6]3+(aq) + 3NH3(aq)à Al(H2O)3(OH)3(s) + 3NH4+(aq)
Reactions with Sodium Carbonate:
- Carbonate ions react differently depending on the oxidation state.
- A precipitate will form, and, in the 3+ reactions CO2 is produced
- The greater acidity of 3+ metal ions means that the carbonate will act as a base and remove protons.
- [Fe(H2O)6]2+(aq) + CO32-(aq) à FeCO3(s) + 6H2O(l)
- [Cu(H2O)6]2+(aq) + CO32-(aq) à CuCO3(s) + 6H2O(l)
- [Fe(H2O)6]3+(aq) + 3CO32-(aq) à Fe(H2O)3(OH)3(s) + 3CO2(g) + 3H2O(g)
- [Al(H2O)6]3+(aq) + 3CO32-(aq) à Al(H2O)3(OH)3(s) + 3CO2(g) + 3H2O(g)

24.2 Ligand Substitution Reactions:
- Complexes containing water molecules can have the water ligands replaced by different ligands.
- Replacement by water or ammonia ligands do not involve a change in coordinate number as they are a
similar size.