Synthesis of Alum Lab This synthesis reaction involves a redox reaction and the formation of a complex ion

Balanced Net Ionic Equations Mole ratios of Al to K to alum are all 1:1. Aluminum hydroxide dissolves in a solution with excess KOH: Al(OH)3(s) + OH-(aq)  [Al(OH)4]-(aq) Aluminum hydroxide dissolving in acid solution: Al(OH)3(s) + 3H+(aq) + 3H2O(l)  [Al(H2O)63+]-(aq) + 3H2O(l)

Lab Discussion Questions Aluminum reacts with KOH and water to form tetrahydroxoaluminate(III) ions, potassium ions and hydrogen gas: 2Al(s) + 2K+(aq) + 2OH-(aq) + 6H2O(l)  2[Al(OH)4]-(aq) + 2K+(aq) + 3H2(g) The oxidation and reduction half reactions: Oxidation: 2Al(s) + 8OH-(aq) + 6H2O(l)  2[Al(OH)4]-(aq) + 6e- Reduction: 6H2O(l) + 6e-  3H2(g) + 6OH-(aq)

Hydrogen ions from the acid react with tetrahydroxoaluminate(III) ions to precipitate aluminum hydroxide: H+(aq) + [Al(OH)4]-(aq)  Al(OH)3(s) + H2O(l) c) Aluminum hydroxide reacts with additional hydrogen ions and water to form hydrated aluminum ions: Al(OH)3(s) + 3H2O(l) + 3H+(aq)  [Al(H2O)6]3+(aq) d) Alum forms from potassium ions, hydrated aluminum ions sulfate ions and water: K+(aq) + 6H2O(l) + 2SO42-(aq) + [Al(H2O)6]3+(aq) KAl(SO4)2.12H2O(s)

Meanings of These Formulae A complex ion consists of a central metal cation (usually derived from a transition metal) joined by coordinate covalent bonds to molecules or anions called ligands. Complex ions can be cations or anions. Compounds composed of a complex ion and counter ions are coordinate compounds Hydrates are indicated by the dot and number of water molecules incorporated into the compound. When finding molar mass of a hydrate, add the indicated number of water molecules (12H2O = (12 x 18 g/mol).

Relationship between coordinate compound and complex ion Counter Ion [Cu(H2O)4]SO4 Cu(H2O)42+ SO42- K[Al(SO4)2] Al(SO4)2- K+ [Al(H2O)6]2(SO4)3 Al(H2O)63+ K3[Fe(CN)6] Fe(CN)63-

Common complex ions The number of ligands (things attached to the metal) is usually double the oxidation number of the metal. Transition metals with NH3, OH-, or SCN- often form complexes. NH3 is added to Cu2+: Cu(NH3)42+ cupric tetraamine NH3 is added to Ag+: Ag(NH3)2+ silver diamine Conc. OH- is added to Zn(OH)2: Zn(OH)42+ Fe3+ in thiocyanate (SCN-): Fe(SCN)63- complex Co2+ with chlorine: CoCl42- Al oxidized in base: Al(OH)4-

Counting the Charges

Naming Coordination Complexes Cation name precedes anion name The complex ion: Ligands are listed first then central metal ion Negative ligands are often named by replacing the ion ending with an –o. (chloro, bromo, nitrito, etc.). Examples of ligand names are chloro, hydroxo, cyano Ligand Names Not Ending in –o: H2O - aqua NH3 - ammine CH3NH2 - methylamine CO - carbonyl NO – nitrosyl S2O32--- thiosulfato

WRITING COMPLEX ION FORMULAS write the central ion first then negative ligands (alphabetical order) then neutral molecules (alphabetical order) polyatomics always in parentheses (even if 1)