1. Complex Ions A complex ion is when cations combine with either molecules or ions of opposite charge (anions) to form a new charged particle. They tend to last only a short time, but complexes have distinct chemical properties. Generally have a central atom (or ion) with joined on particles called ligands. The use of square brackets indicates it is a complex ion

2. Types of Complex ions Complex ions form with the hydroxide and ammonia anions Hydroxide with Zinc or Aluminium Ammonia with Silver, zinc or copper

3. Complex Ion Colours [Cu(NH 3 ) 4 ] 2+ [FeSCN] 2+ [Zn(NH 3 ) 4 ] 2+ [Zn(OH) 4 ] 2- [Al(OH) 4 ] - [Ag(NH 3 ) 2 ] +

4. Aluminate If sodium hydroxide is added to a solution containing Al 3+ insoluble aluminium hydroxide is formed. 3OH - (aq) + Al 3+ (aq) Al(OH) 3 (s) If hydroxide ions are added to aluminium hydroxide soluble aluminate ions form. Al(OH) 3 (S) + OH - (aq) [Al(OH) 4 ] - (aq)

5. Zinc Hydroxide Complex If sodium hydroxide is added to a solution containing Zn 2+ insoluble Zinc hydroxide is formed. 2OH - (aq) + Zn 2+ ( aq) Zn(OH) 2 (s) If hydroxide ions are added to Zinc hydroxide soluble Zinc hydroxide complex ions form. Zn(OH) 2 (s) + OH-(aq) [Zn(OH) 4 ] 2- (aq)

6. Ammonia Solutions Solutions of ammonia contain Ammonia molecules (NH 3 ) Water molecules (H 2 O) A few hydroxide ions (OH - ) Ammonium ions (NH 4 + ) This is because ammonia is a weak base Small volumes of ammonia solution behave the same way as hydroxide solutions. Large volumes can lead to the formation of complex ions

7. Silver diammine ion In ammonia solutions silver ions form a precipitate of brown silver oxide. 2Ag + (aq) + 2OH - Ag 2 O(s) + H 2 O(l) Additional ammonia forms soluble silver diammine. Ag 2 O (s) + H 2 O (l) + 4NH 3 (aq) 2[Ag(NH 3 ) 2 ] + (aq) + 2OH - (aq) Silver chloride also does this AgCl(s) + 2NH 3 (aq) 2[Ag(NH 3 ) 2 ] + (aq) + Cl - (aq)

8. Zinc Tetraammine ion Zinc precipitates as white zinc hydroxide Zn 2+ (aq) + 2OH - (aq)Zn(OH) 2 (s) Excess ammonia gives soluble Zinc Tetraammine. Zn(OH) 2 (s) + 4NH 3 (aq)[Zn(NH 3 ) 4 ] 2+ (aq) + OH(aq)

9. Copper tetra-ammine ion When a little dilute ammonia is added to copper sulphate a light blue precipitate of copper hydroxide forms Cu 2+ (aq) + 2OH - (aq)Cu(OH) 2 (s) Excess or concentrated ammonia solution results in the formation of a deep blue solution of copper tetra- ammine ion Cu(OH) 2 (aq) + 4NH 3 (aq) [Cu(NH 3 ) 4 ] 2+ (aq) + 2OH - (aq)

10. Review Solubility 1.Which cations have insoluble sulfates? 2.Which cations have insoluble chlorides? 3.Which ions have soluble carbonates? 4.Which ions form white hydroxides? 5.Which ions form a complex with hydroxide? 6.Write the formulae for three ammonia complexes.

11. Answers to: Solubility facts 1.Pb2+, Ca2+, Ba2+ (Ag+) 2.Pb2+, Ag+ 3.Na+, K+, NH4+ 4.Mg2+, Pb2+, Zn2+, Al3+ 5.Pb2+, Zn2+, Al3+ 6.[Ag(NH3)2]+, [Cu(NH3)4]2+, [Zn(NH3)4]2+

12. Homework Make flash cards to learn your complex ions

13. Complete work sheet 18: Soluble or Insoluble 1 insoluble 10 insoluble 2 11 soluble 3 insoluble 12 insoluble 4 13 soluble 5 slightly soluble 14 insoluble 6 soluble 15 soluble 7 16 slightly soluble 8 soluble 17 insoluble 9 18 soluble