If no crystals have formed after 30 minutes, consult your instructor.
Let the filtrate beaker sit undisturbed in the ice bath until crystals of alum are observed. Place 3 mL of 95% ethanol into a test tube, and put the test tube in a second ice bath, secured by a test tube clamp. Place the filtrate beaker into the ice bath, making sure no water from the ice bath gets into the filtrate beaker. Allow it to begin to cool while you prepare an ice bath, an ice-water mixture in a 400-mL beaker. Using tongs, remove the filtrate beaker to a wire gauze on the lab bench. Reaction steps involving the sulfuric acid:. Using a hot plate, heat the acidified filtrate until all solid dissolves. Observe and record changes in the filtrate. Slowly and carefully stir 22.5 mL of 4 M H 2SO 4(aq) into the filtrate in approximately 5-mL portions. When all the liquid has drained from the filter paper, discard the paper and its contents in the appropriate waste container. Rinse the residue on the filter paper with 2-3 mL of distilled water, joining this rinse to the filtrate. Rinse the reaction beaker twice with 2 mL distilled water, and add each rinse to the filter paper. Transfer the reaction mixture to the filter paper in the funnel. Moisten the filter paper with 2-3 mL of distilled water to make it adhere to the funnel, and discard this water. Fold a 7-cm piece of filter paper as described in the lab handout. Place a funnel in your funnel holder, and place a labeled beaker beneath the funnel. Gravity filtration of the reaction mixture. On your data sheet, describe the reaction mixture after all the Al dissolves. Use your rubber policeman to push back into the solution any Al that adheres to the side of the beaker. Use only the glass part of your stirring rod to wet the Al. Under the fume hood, pour 13.0 mL of 3.0 M KOH into the reaction beaker. Place the foil in a reaction beaker labeled with your initials. Weigh 0.45-0.50 g Al foil, using the tare function on the balance and not letting the foil come into contact with your hands or the balance pan. The synthesis will be carried out in the following stages: It is not a substitute for reading the procedure in the handout before coming to lab. This is a brief summary of that procedure including tips, suggestions, and deviations from the procedure detailed in the handout. Theoretical yield, g Procedure Note: the following is not a procedural check-list that is contained in the lab handout. Theoretical yield = grams Al used x - x - x - = g alum per cent yield: quantity of product actually recovered expressed as a percentage of the theoretical yield. theoretical yield: quantity of product expected based on quantity of limiting reagent used. 
recrystallization: isolation and purification of a solid by causing it to precipitate slowly from solution. vacuum filtration: filtration using filter paper in a specially designed funnel (Büchner funnel) to separate solids from a liquid pulled through the funnel under vacuum. gravity filtration: ordinary filtration using filter paper in a funnel to separate solids from a liquid allowed to flow freely (under gravity) through the funnel. Synthesis of Alum Synthesis of Alum, KAl(SO 4) 2.
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