AlumLab - Synthesis of Alum Lab Synthesis This synthesis...

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Unformatted text preview: Synthesis of Alum Lab Synthesis This synthesis reaction involves a This redox reaction and the formation of a complex ion complex Balanced Net Ionic Equations Balanced Mole ratios of Al to K to alum are all 1:1. Aluminum hydroxide dissolves in a solution with Aluminum excess KOH: excess 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) (aq) 3H (aq) 3H Lab Discussion Questions Lab a) Aluminum reacts with KOH and water to form Aluminum tetrahydroxoaluminate(III) ions, potassium ions and hydrogen gas: and 2Al(s) + 2K+(aq) + 2OH-(aq) + 6H2O(l) 2[Al(OH)4]-(aq) + 2K+(aq) + 3H2(g) 2Al The oxidation and reduction half reactions: Oxidation: 2Al(s) + 8OH-(aq) + 6H2O(l) 2[Al(OH)4]-(aq) + 6eReduction: 6H2O(l) + 6e- 3H2(g) + 6OH-(aq) (g) 6OH a) a) Hydrogen ions from the acid react with Hydrogen tetrahydroxoaluminate(III) ions to precipitate aluminum hydroxide: aluminum H+(aq) + [Al(OH)4]-(aq) Al(OH)3(s) + H2O(l) c) Aluminum hydroxide reacts with additional hydrogen Aluminum ions and water to form hydrated aluminum ions: ions Al(OH)3(s) + 3H2O(l) + 3H+(aq) [Al(H2O)6]3+(aq) d) Alum forms from potassium ions, hydrated aluminum d) ions sulfate ions and water: ions K+(aq) + 6H2O(l) + 2SO42-(aq) + [Al(H2O)6]3+(aq) KAl(SO4)2.12H2O(s) Meanings of These Formulae Meanings A complex ion consists of a central metal cation complex (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 Compounds ions are coordinate compounds coordinate Hydrates are indicated by the dot and number of Hydrates water molecules incorporated into the compound. When finding molar mass of a hydrate, add the indicated number of water molecules (12H2O = (12 x indicated (12 18 g/mol). 18 Relationship between coordinate compound and complex ion compound Coordinate Compound [Cu(H2O)4]SO4 Complex Ion Counter Ion Cu(H2O)42+ SO42- K[Al(SO4)2] [Al(H2O)6]2(SO4)3 K3[Fe(CN)6] Al(SO4)2Al(H2O)63+ Fe(CN)63- K+ SO42K+ Common complex ions Common The number of ligands (things attached to the metal) is The usually double the oxidation number of the metal. Transition metals with NH3, OH-, or SCN- often form Transition complexes. 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: CoCl42Al oxidized in base: Al(OH)4- Counting the Charges Counting Naming Coordination Complexes Naming Cation name precedes anion name The complex ion: Ligands are listed first then central metal ion Ligands Negative ligands are often named by replacing the ion Negative ending with an –o. (chloro, bromo, nitrito, etc.). Examples of ligand names are chloro, hydroxo, cyano Ligand Names Not Ending in –o: H2O - aqua aqua NH3 - ammine NH CH3NH2 - methylamine CO - carbonyl NO – nitrosyl S2O32--- thiosulfato WRITING COMPLEX ION FORMULAS FORMULAS write the central ion first then negative ligands (alphabetical order) then neutral molecules (alphabetical order) polyatomics always in parentheses (even if 1) ...
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This note was uploaded on 12/01/2010 for the course PHYS PHYS320 taught by Professor Garrett during the Spring '10 term at DeVry Chicago.

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