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Experiment3Alum copy

Experiment3Alum copy - Experiment#3 Recycling Aluminum...

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Experiment #3: Recycling Aluminum
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Purpose: The purpose of this experiment was to scale down a protocol to synthesize a theoretical yield of 23 grams (g) of alum through gravity and vacuum filtrations. Following isolation of crystals of alum, percent yield and melting point (to determine purity) were to be calculated. Results and Discussion: A series of filtration reactions were carried out to produce the alum. The net reaction throughout the experiment is shown below: 2Al(s) + 2KOH(aq) + 4H 2 SO 4 (aq) + 22H 2 O(l) 2KAl(SO 4 ) 2 •12H 2 O(s) + 3H 2 (g) It is important to note that during the first heated reaction in this experiment, shown below, the solution involved bubbled over the original beaker too much and the reaction was taken off heat momentarily and transferred to a larger beaker. 2Al(s) + 2KOH(aq) + 6H 2 O(l) 2K + (aq) + 2Al(OH) 4 - (aq) + 3H 2 (g) The products were filtered and combined with a small amount of sulfuric acid, producing a white solid precipitate: Al(OH) 4 - (aq) + H + (aq) Al(OH) 3 (s) + H 2 O(l) The solution was stirred and remaining sulfuric acid was added incrementally as the solution became more clear: Al(OH) 3 (s) + 3H + (aq) Al 3+ (aq) + 3H 2 O(l) After a second gravity filtration, the solution was put on ice to cool so that Al 3+ could react with potassium and sulfate ions in solution to form the hydrated crystal alum precipitate, as: K + (aq) + Al 3+ (aq) + 2SO 4 2- (aq) + 12H 2 O(l) 2KAl(SO 4 ) 2 •12H 2 O(s) + 3H 2 (g) In this trial, crystal was not observable after nearly 15 minutes of cooling on ice, and the sides of the beaker of solution were scratched with a glass rod to induce crystallization. The formation of a white, crystal precipitate was then observed on the bottom of the beaker. This precipitate was vacuum filtered and dried for a week. Following the filtration reactions and drying of alum, the synthesized alum crystals were massed on a calibrated electronic scale. To acquire the crystal mass, first (before drying), the tray and filter paper used were placed on the scale. The reading acquired was 7.44 g.
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