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Unformatted text preview: Discussion: The overall purpose of this lab is to synthesize alum, KAl(SO 4 ) 2 12H 2 O. After synthesizing, the alum is tested for the presence of K + , Al 3+ , SO 4 2- , and H 2 O in KAl(SO 4 ) 2 12H 2 O . The aluminum foil is treated with the base KOH. Aluminum metal and aluminum oxide react independently with KOH to form potassium aluminate. The potassium aluminate reacts with sulfuric acid to form solid aluminum hydroxide, Al(OH) 3 (s). The solution is then heated and excess sulfuric acid is added to neutralize the hydroxide, dissolving the aluminum hydroxide. The result is the production of Al 3+ and SO 4 2- ions. The solution now contains these ions, and evaporation saturates the solution. I t is then cooled in an ice bath to form alum crystals: K + (aq) + Al 3+ (aq) + SO 4 2- + 12 H 2 O(l) KAl(SO 4 ) 2 12H 2 O(s) Part 1. Synthesis of Alum from Aluminum Foil 0.515 g of aluminum foil is placed in a flask and 25 mL of 4M KOH is added slowly: 2 Al (s) + 2 OH- (aq) + 6 H 2 O (l) 2 Al(OH)- 4 (aq) + 3 H 2 (g) The foil dissolved and formed an aqueous solution of aluminum hydroxide and hydrogen gas. When the reaction was complete, all of the foil had dissolved and a black solute at the bottom of the solution formed. The solution was then placed on the hotplate until all of the aluminum had reacted. The black solute at the bottom was filtered out of the solution and reacted....
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This note was uploaded on 12/02/2009 for the course CHEM chem1C taught by Professor O'dea during the Spring '09 term at UCSB.
- Spring '09