Alum Synthesis: The Chemical Process of Recycling Aluminum Introduction By recycling aluminum cans, the costs and energy savings are dramatically more resourceful and efficient than producing aluminum from what it is naturally found in, bauxite ore. The process of recycling aluminum to produce potassium aluminum sulfate, a common alum, will be done through a serious of chemical reactions. Through this reaction, percent yield will be determined. Materials and Methods The mass of a 250 mL beaker is measured, and . 9 to 1. 2 grams of aluminum can pieces are added to the beaker. The mass of the beaker and aluminum pieces is recorded.
These two masses are then used to determine the initial mass of aluminum being reacted in this experiment. 50 mL of 1. 4 M KOH is then added to the beaker and placed upon a hot plate under a fume hood to fumigate any escaping gases during the reaction, which should take no longer than 30 minutes. The heat from the hot plate speeds the reaction, and the reaction mixture must be kept no lower than 25 mL by adding distilled water. An aspirator is assembled by using a suction flask, clamp, ring stand, rubber tubing, funnel, and filter paper to filter the reaction mixture once the first reaction is complete.
The filter paper is then wetted, the vacuum source is turned on, and the mixture is poured through the filter, using 5 mL of distilled water to rinse the beaker. The filter will catch all the dark filtrate from the aluminum can pieces, and the suction flask will contain a clear (transparent) solution. The solution is then transferred to a clean 250 mL beaker, and the suction flask is rinsed with 10 mL distilled water to insure all the remaining solution is transferred to the clean beaker. The beaker is placed in an ice bath to cool the solution, filling the beaker three fourths full with ice and cold water. 0 mL of 6. 0 M sulfuric acid is measured and slowly added to the mixture, using a stirring rod to mix. Heat the mixture on a hot plate if any solids begin to develop in the mixture. Using a 1 L plastic beaker, prepare another ice bath and place the beaker containing the reaction mixture in the ice bath. Once in the ice bath, the alum crystals forming in the mixture will begin to precipitate. To help the process of crystal formation, use the stir rod to scrape the sides of the beaker and form an alum seed crystal. Reassemble a clean vacuum filter, and filter the crystals onto the filter paper.
This type of reaction is a redox (reduction-oxidation) reaction, where the aluminum metal is oxidized to aluminum with an oxidation number of +3 and the hydrogen in potassium hydroxide or in water is reduced from an oxidation number of +1 to zero in hydrogen gas. The balanced chemical equation for this reaction is: 2Als+ 2KOHaq+ 6H2Oliq>2KAlOH4aq+ 3 H2g During this reaction, the colorless mixture potassium hydroxide and aluminum pieces turned a dark, ashy gray as heat was applied and the aluminum can pieces dissolved. The heat sped the reaction, and within thirty minutes all the aluminum pieces were dissolved, leaving behind aluminate.
In the second reaction, the filtered aluminate solution is mixed with sulfuric acid once the solution has cooled. After stirring for several minutes, crystals began to form. The crystalizing liquid started thickening and appeared to be white. The product of this reaction is aluminum hydroxide, potassium sulfate, and water. The fully balanced chemical equation is: 2 KAl(OH)4(aq) + H2SO4(aq) >2Al(OH)3(s) + 2 H2O(liq) + K2SO4(aq) This equation represents a metathesis (precipitation) reaction where all the elements and groups recombine and a precipitate, aluminum hydroxide, is formed.
As more sulfuric was added, the precipitate began to dissolve, thus causing the third reaction. The solution contains aluminum, potassium, and sulfate ions now. The balanced chemical equation is: 2 Al(OH)3(s) + 3 H2SO4(aq) >Al2(SO4)3(aq) + 6 H2O(liq) This type of reaction is a metathesis (acid-base) reaction where, once again, the elements and groups recombine themselves. The product of this reaction is aluminum sulfate and water. The solution continued to cool and crystals began to form. The last reaction resulted in a hydrated potassium aluminum sulfate, and crystals of this compound formed slowly. Seed crystals” developed and more alum deposited causing the crystals to expand. The balanced chemical reaction is: Al2(SO4)3(aq) + K2SO4(aq) + 24 H2O(liq) >2 KAl(SO4)2•12 H2O(s) This would be considered a combination reaction because the three reactants combined to form one product, hydrated potassium aluminum sulfate. The overall balanced chemical reaction for this experiment is: 2Al(s)+2KOHaq+4H2SO4(aq)+22H2O(liq) >2 KAl(SO4)2•12H2O(s) + 3 H2(g) At the start of the experiment, 1. 01 grams of aluminum can pieces were used. After forgoing several reactions, 4. 19 grams of alum were recovered.
Theoretically, 17. 76 grams of alum should have been recovered. This gives a percent yield of 24. 0%. Human error was definitely the main factor as to why the percent yield is not anywhere close to 100%. My lab partner and I did have a misunderstanding with one of the steps in the instructions; instead of placing the beaker in an ice bath during reaction three, we thought the directions said to put ice directly into the reaction mixture. This may have caused some error in the cooling process of the mixture, and may have not enabled all the crystals to form properly.
We may have also not waited long enough for all the crystals to form. Also, some of the crystals may have gotten lost while being transferred from the beaker, to the aspirator, and then to another beaker to be measured. These factors are reasonable as to why the actual yield of alum that resulted in the experiment were not accurate with the theoretical yield of alum. Conclusion Through a series of reactions, it is understood that aluminum can be chemically reacted to result in the synthesis of alum. The success of the experiment proves the reasoning of the process of recycling aluminum.