Aluminum Recycling By Lionel Sims III
Lab Instructor: Roy October 12, 2007
Results and Discussion:
Aluminum strips were used in the obtainment of alum, alum is a name given to a group of chemicals with the general formula MM' (SO4)2 12H2), where M is a monovalent cation and M' is a trivalent cation. The particular form of alum synthesized in this experiment was potassium aluminum sulfate dodecahydrate [KAl(SO4)2 12 H2O], in the solid form of crystals, through a series of chemical reactions. A theoretical yield of 23g was expected. The net of these reactions is shown by the reaction below: 2 Al(s) + 2 KOH(aq) + 4 H2SO4(aq) + 22 H2O(l) 2KAl(SO4)2 12H2O(s) + 3H2(g) During the first week of the experiment, four different reactions took place, numbered 1-4 below. 1. 1.31g of Aluminum strips were cut from a soda can and added to 66 ml of 1.4M KOH and heated on hot plate. The solution was watched until it stopped releasing H2. The new solution began to turn black and the Al almost completely dissolved in it. The solution had to then be filtered using gravity filtration in order to remover any solids that may have been on or in the can along with the Al. The filtered solution was clear because the filter paper held black residue. About 50 ml of solution was obtained in this step. The chemical reaction was as follows, the arrow indicates the introduction of heat: 2 Al(s) + 2 KOH(aq) + 6 H2O 2 K+(aq) + 2 Al(OH)4(aq) + 3 H2(g) 2. 6 ml of 9M H2SO4 was added to this new solution, as it was added the solution began to turn white and cloudy. Al(OH)4-(aq) + H+(aq) Al(OH)3(s) + H2O(l) 3. 20 ml of 9 M H2SO4 was added in the next step. While the new solution was mixed it was slowly heated and stirred. The solution turned even foggier and then cleared. It was then filtered for residue. Al(OH)3(s) + 3 H+(aq) Al3+(aq) + 3H2O(l) 4. The new clear solution and a 15 ml 1/1 ethanol/water mixture were both placed in an ice bath and allowed to chill as the white alum crystals formed. The reaction K+(s) is: + Al3+(aq) + 2 SO42- + 12 H2O(l) KAl(SO4)2 12 H2O The solution then had to be completely filtered in order to weigh the alum crystals. So the water/ethanol mixture was used to rinse all of the crystals from the beaker into the
funnel of the vacuum filter. The crystals were completely filtered and allowed to sit and dry for the next weeks experiments. The purpose of week two was to measure the amount of alum formed and discover its melting point in order to test its purity. MASS Empty weighing boat 6.780 Weighing boat with crystals 17.068 Alum 10.288 Mass of alum was determined thusly: (Mass of bottle w/ alum) (Mass of empty bottle) = (Mass of alum) Percent Yield of alum:
experimantal result *100 Percent Yield (%) theoretical result
10.288g *100 = 44.73% 23 g
Samples of the alum were then placed in capillary tubes in order to place them in a hot water bath to determine its melting point. Four different trials were done with four different samples before reproducibility was produced. TRIAL (#) MELTING POINT RANGE ( C) AVERAGE TEMPERATURE ( C) 1 88-91 89.5 2 89-90 89.5 3 90-92 91 4 89-90 89.5 Average melting point: 89.9 C Known melting point: 92.5 C Percent Error:
accepted value - mean value accepted value 92.5 89.9 92.5 100 2.81%
100 = Percent Error(%)
Average Deviation:
89.9 89.5 89.9 89.5 4 89.9 91 89.9 89.5 0.58
Relative Average Deviation: 0.58 89.9 Conclusion:
100 0.65%
The alum synthesized in this experiment was considered to be relatively pure. Due to the percent error being only 2.81%, this is a small amount of error and can be attributed to impurities due to the laboratory mishap that led to the alum being spilled out onto the floor after being weighed. The samples used in the melting point trials were taken from the spilled alum. The relative average deviation was below one percent showing the results to contain an adequate degree of precision. And the percent yield was acceptable due to the many filtrations and opportunities for human error.