University:
Eastern Kentucky University
Course:
CHE 111 | General Chemistry
Academic year:

2020
Views:

199

Pages:

4
Author:

Carina Becker

Synthesis of Aluminum Experiment 9 Introduction Alum is a group of crystalline substances, that usually contain an aluminum sulfate, a water of hydration, and another element. This experiment will be synthesizing the particular alum known as potassium aluminum sulfate dodecahydrate (KAl(SO4)212H2O). To achieve this synthesis aluminum foil will be dissolved in a strong base and then filtered, and this new solution will be mixed with a strong acid. This aqueous solution will be given time to evaporate off the water leaving behind the desired crystals. A mixture of both physical and chemical processes occur with the synthesis of alum. In this experiment, a sample of alum will be synthesized and that will be compared to its theoretical yield. Materials and Procedure Attached as a carbon copy of the pre-lab. Calculations Weighed Mass of Aluminum: 1 gram Weighed Mass of the Alum: 3.81 grams Moles of Aluminum: 1/26.98= 0.037106 mol Ratio of Aluminum to Alum= 1:1 Moles of Alum formed= 0.037106 mol Mass of Alum= 0.037106 x 474.19 =17.58 g Percent yield = (actual mass/theoretical mass) x 100% Percent yield = (3.81/17.58)x100= 21.67% Discussion 1.) The theoretical yield of alum is 17.58 grams. 2.) The percent yield of our crystal was 21.67% 3.) There are a few factors that can affect percent yield including; temperature, container, pressure, medium, and physical state. 4.) Balanced Net Ionic Equations a.) 2Al (s) + 2OH- (aq) + 6H2O (l) b.) H+ (aq) + 2[Al(OH)4]- (aq) 2[Al(OH)4]- (aq) + 3H2 (g) Al(OH)3 (s) + H2O (l) c.) Al(OH)3 (s) + H+ (aq) + 3H2O (l) [Al(H2O)6]3+ (aq) d.) K+ (s) + [Al(H2O)6]3+ (aq) + 2SO42- (s) + 6H2O(l) KAl(SO4)212H2O 5.) A synthesis reaction is when several reactant species combine to produce a more complex product species. 6.) When the alum was being synthesized it was in a solvent of KOH, until sulfuric acid was added to neutralize the strong base into water, this was an exothermic reaction. The solution was very hot at this point, but as it cooled and the water evaporated off alum crystals began to form. 7.) It was a cloudy substance taking on a ridge crystal shape, the geometry varied from crystal to crystal. Observations While conducting the lab there are several recognizable observations. When the aluminum foil was mixed with the strong base KOH it was a very rapid and extreme exothermic reaction. Within a minute almost all of the aluminum foil was dissolved and the beaker was heated up to the point it should be handled with gloves. The reaction caused the aluminum to smoke while it dissolved, and also let off a smelly fume. Once the strong acid was added to the mixture it formed an aqueous solution, it was intriguing to observe once the water evaporated left behind crystals. This reinforces several chemistry principles, including acid-base principles and the basis of chemical reactions. I now have a more clear understanding of how synthesis of Alum works in part to these observations. Conclusion In the lab conducted, we were able to successfully synthesize an alum crystal from aluminum foil. The percent yield of the alum was about twenty-two percent, which is good for this experiment. The major error in this yield is due in part to the impurities in the aluminum foil. All in all, the lab clearly shows how a species is synthesized and that the percent yield will never be one-hundred percent.