Saul Ruiz Chemistry 1CL April 22 2012 Experiment 16 Synthesis of Alum This experiment dealt with the synthesis of alum KAl SO4 2 12H2O from aluminum foil as well as performing various qualitative tests such as the flame test for the presence of K Al3 SO42 and H2O in the alum This second part of the experiment dealt with growing alum crystals using various crystal growth techniques In the first part of the experiment 0 5 grams of aluminum foil are weighed and cut into smaller pieces in order to increase the surface area of the aluminum Then they are placed in a 250 mL Erlenmeyer flask after which 25 mL of KOH is added and the flask is swirled After completing this process it was observed that white foam began to appear along with bubbling fizzling and a heating of the solution This can be seen through the reaction OH aq 6 H 2 O l 2 Al 2 Al s 2O H After the reaction has slowed down the flask is gently heated on a hot plate until all the aluminum has reacted This warm mixture is filtered through a filtration apparatus and then transferred to a clean dry 250 mL flask where 20 mL of 9M H2SO4 is added After swirling the flask an aluminum hydroxide precipitate formed The flask is then heated until the volume of the solution reaches 35 mL and all of the precipitate dissolves according to the reaction OH 3 aq 3 H 2 O l aq Al Al The flask is then allowed to equilibrate to room temperature and later placed in an ice bath from which alum crystals should form O4 S 2 aq 12 H 2 O l KAl 3 aq 2 SO 4 aq Al K O4 S 2 Al s 2 KOH 22 H 2 O 4 H 2 SO 4 2 KAl The results for the theoretical yield in this part of the experiment were 8 7854 grams of alum whereas the actual was 17 090 grams of alum Furthermore the percent yield that was obtained for alum was 194 5 The reason that is over 100 is that difficult to obtain completely dry crystals using suction which possibly results in a percent yield over 100 For the KOH and BaCl2 test two small test tubes are cleaned and a spatula of alum is placed in each In the first test tube a few drops of BaCl2 are placed which causes the reaction 2 aq 2 Ba S O4 s 2 aq 2 Ba Net Ionic 2 S O 4 This also forms a white powdery foamy precipitate on top of the test tube In the second test tube 0 1 M KOH is added drop wise which forms a very small amount of white ish precipitate on the top of the test tube OH aq Al 3 aq 3O H Net Ionic Al In order to test for the presence of water thus the hydrates in the alum crystal a spatula of alum is added to a clean test tube and heated over a flame after which condensation appeared on the side of the test tube For the flame test two small test tubes are obtained and a spatula of alum is added to one of the test tubes whereas potassium chloride is added to the second The crystals in each of the test tubes are dissolved in a few milliliters of DI water Afterwards the nichrome wire is dipped into the KCl solution and placed over the flame of the Bunsen Burner which reveals a faint purplish pinkish flame This color change is due to the potassium ion being present in the KCl solution which gives it a lilac color when placed over the flame When the nichrome wire is dipped into the alum mixture and placed over the flame it appears to be the same color as the potassium chloride solution Some possible sources of error for this experiment arise from the fact that there could have been an accidental inclusion of other substances when the mass of synthesized alum was measured If the alum is mixed with any of the other chemicals in the lab or the filter paper they would affect the final results