Presentation on theme: "Synthesis of Alum Lab This synthesis reaction involves a redox reaction and the formation of a complex ion."— Presentation transcript:
1 Synthesis of Alum LabThis synthesis reaction involves a redox reaction and the formation of a complex ion
2 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)
3 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)
4 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)
5 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 compoundsHydrates 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).
6 Relationship between coordinate compound and complex ion Counter Ion[Cu(H2O)4]SO4Cu(H2O)42+SO42-K[Al(SO4)2]Al(SO4)2-K+[Al(H2O)6]2(SO4)3Al(H2O)63+K3[Fe(CN)6]Fe(CN)63-
7 Common complex ionsThe 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 tetraamineNH3 is added to Ag+: Ag(NH3)2+ silver diamineConc. OH- is added to Zn(OH)2: Zn(OH)42+Fe3+ in thiocyanate (SCN-): Fe(SCN)63- complexCo2+ with chlorine: CoCl42-Al oxidized in base: Al(OH)4-
9 Naming Coordination Complexes Cation name precedes anion nameThe complex ion:Ligands are listed first then central metal ionNegative ligands are often named by replacing the ion ending with an –o. (chloro, bromo, nitrito, etc.).Examples of ligand names are chloro, hydroxo, cyanoLigand Names Not Ending in –o:H2O - aquaNH3 - ammineCH3NH2 - methylamineCO - carbonylNO – nitrosylS2O32--- thiosulfato
10 WRITING COMPLEX ION FORMULAS write the central ion firstthen negative ligands (alphabetical order)then neutral molecules (alphabetical order)polyatomics always in parentheses (even if 1)
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