October 6, 2010
The purpose of this laboratory project was threefold, in that it presented three main objectives. The first objective was to prepare the ionic compound alum from aluminum powder. The alum was produced from the reduction-oxidation reaction of aluminum with potassium hydroxide and sulfuric acid in water. The second objective was to then analyze the alum product for water crystallization; that is, to determine the value of x in the following formula: KAl(SO4)2(aq) xH20
After the formula of the product had been deduced, it was then possible to complete the third and final objective of the project, which was to calculate the theoretical yield, the actual yield, and then the percentage yield of the preparation. These yields were surmised by using specific stoichiometric calculations. Experimental Method
To form alum, 0.50 g of aluminum powder (Al(s)) were added to 2.01 g of Potassium Hydroxide (KOH(aq)) in a 400 mL beaker. Under the hood, 25 mL of distilled water were then added to the beaker. The mixture was stirred with a glass strirring rod in order to disperse the heat produced by this exothermic reaction. After about 15 minutes, when there was no sign of further evolution of hydrogen, the solution was filtered by gravity into a 250 mL beaker. Any residue was washed from the filter paper with distilled water and collected in the filtrate. While stirring, approximately 10 mL of 9 M H2SO4 solution was carefully poured into the filtrate. The H2SO4 neutralized the solution, producing a thick, gelatinous precipitate of Al(OH)3. After this was completed, the mixture was gently warmed on a hot plate, with the temperature being raised 5C every two minutes, starting at 65C. Within ten minutes, the blue litmus paper used to test the acidity of the solution turned red, thus showing that the solution was acidic. 1 mL more acid was added to the solution in to dissolve the remaining solid particles....