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~~ Chem 207 Lab - Report 3

~~ Chem 207 Lab - Report 3 - Results and Discussion A given...

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Results and Discussion:   A given procedure was scaled down in order to prepare a theoretical yield of 23 g of alum. In  order to synthesize the alum from aluminum, both gravity and vacuum filtrations were performed. After  being crystallized and isolated, the percent yield and melting point of the solid alum were determined. An aluminum soda can was cut into tiny strips. The mass of these strips was found to be 1.295  grams using a highly calibrated balance. After finding the mass, the strips were then placed into an empty  600-mL beaker. In the fume hood, 67 mL of 1.4 M KOH was added to the 600-mL beaker containing the  aluminum strips and the mixture was heated gently for about 30 minutes. A reaction occurred while  heating, causing the aluminum strips to dissolve and a gas (H 2 ) to be produced. This reaction is  demonstrated by the following equation: 2 Al (s)  + 2 KOH (aq)  + 6 H 2 O (l)    2 K + (aq)  + 2 Al(OH) 4 - (aq)   + 3 H 2(g) About 40% of the evaporated water was replaced with distilled water. Then, the product of the  previous reaction was filtered using gravity filtration, and a faint clearish-yellow solution was obtained in  a clean beaker. 26.5 mL of 9M H 2 SO 4  was measured using a graduated cylinder and was gradually added  to the clearish-yellow solution in the beaker while it was being warmed on a hot plate.  After the first 6.5 mL of sulfuric acid was added to the beaker, a thick, white precipitate formed,  which can best be understood in terms of the following equation.
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