Ap Chem Lab Report
The objective of this lab is to run tests on a compound and analyze the substance itself, and then determine whether or not the compound is actually alum.
Jill Cline Period 3 November 19, 2013 Laurel Hergenroeder and Sarinah Martelli Introduction/Purpose The purpose of this experiment is to run various tests on the substance called alum. (AIK(S04)2 12H20). These tests like the process of filtration heating the solution will reveal things such as melting point, percent hydrate, as well as percent sulfate.
After the experiment, the experimental mole ratio of alum to water will be alculated and then compared with the accepted mole ratio. (This is 12 to 1). Theory If this lab if conducted properly, the unknown substance will be determined to be alum because of melting point, percent hydration and percent sulfate.
The first test that will be run has the purpose of revealing the alum’s melting point. Melting is defined as, the temperature at which a solid turns into a liquid. The melting point will help determine if the substance is an alum if its melting point is around 92. 0 because this is the accepted melting point of an alum. Then, the water will be vaporated from the substance, which will make it possible to find the percent hydration of the alum. A hydrate is a compound containing water: a chemical compound containing water molecules that can usually be expelled by heating.
Anhydrous also will be a part of this lab because an anhydrous means to be with no water: describes compounds that contain no water, or crystals that lack chemically bound water of crystallization.
The water will be expelled from the substance and Since the mass of the alum will be recorded before as well as after the water is vaporated, the two measurements will simply be divided (the larger as the denominator), yielding the percent hydration. Water of hydration is the amount of water present in hydrated compounds. The accepted mole ratio is 12 H20 moles to 1 mole of AIK(S04)2. The percent hydration and mole ratio will be another indicated if the substance is in fact an alum or not. The third test of alum will have the objective of finding the percent sulfate.
In the experiment, alum will be mixed will be mixed with barium nitrate to yield barium sulfate: (AIK(S04)2(aq) H20 + 2Ba(N03)2(sF2BaS04(s) = AIK(N03)2(aq). But the sulfur reactions, combines with the barium to yield barium sulfate. This percent mass will be found also with the percent mass of barium sulfate and used to find the percent sulfate of the alum. This calculation can only be performed with the prior knowledge of knowing that the barium in the experiment is the excess reagent. This guarantees that the sulfate will all be combined with the barium in the right side of the reaction.
This means that none of the sulfate will be left unprecipitated, allowing the mass of that sulfate in BaS04 to be the mass of sulfate in alum. If all of the sulfate reacts, the percent ulfate should be 40. 490. *H20 + Bas04 + K+ + A13++ N03- In the above reaction, the aluminum and potassium quit their bonds with the sulfate. They abandon, so to speak, the sulfate, and become ionic substances (which explain the charges of the elements in the right side of the equation). Also, the barium abandons its bond with nitrate too, which makes the nitrate an ionic compound in the right side of the equation as well.
The two substances left over, the barium and sulfate, combine to make barium sulfate. This barium sulfate will be used to calculate the percent yield of sulfate in alum. Then, after all three of these experiments with their respective calculations are preformed, the percent error of each will be found. Procedure Melting Point: 1. A small amount of dry alum was pulverized by a mortar and pestle. 2.
The alum was packed into a capillary tube to a depth of . 5cm. 3. Then, to pack the alum in the capillary, the tube was bounced upside-down on the lab table. 4. The capillary tube was fastened to the thermometer.
. The thermometer was fastened to a ring stand. 6. The thermometer and capillary tube was then submerged into a beaker full of water and heated. As the temperature reached about 900 the heating was slowed or stopped. 7.
As the first crystal melted, the temperature was recorded along with the point of all crystals melting. Determination of water hydration in alum 1. A Bunsen burner was set on a ring stand beneath a ring clamp holding a clay triangle. 2. The height of the ring stand was adjusted so that the bottom of the crucible was about lcm above the hottest part of the flame.
. Then the crucible was heated well for about five minutes. 4. When the heating was completed, the crucible was cooled and massed. 5.
Then about two grams of alum was put into the crucible. 6. With a lid covering most of the crucible, it was heated slowly at first, and then on high. 7. After the bubbling inside had stopped, the crucible was heated for about five Determination of the percent sulfate 1. A filter crucible was placed in a small beaker and dried in an oven over night.
2. Using an analytical balance, about 1. 0g of alum was measured and placed into the dried crucible. . This was then dissolved in a 250mL beaker with about 50mL of distilled water.
4. Approximately 50. 0mL of . 200M Ba(N03)2 was added to the issolved alum, which was then stirred until the substance was dissolved. 5. The beaker was covered and heated near boiling point for about 15 minutes.
6. The filter paper was massed. 7. The mixture was poured from above into the filtration system. 8. Once the filtering was complete, the solution was filtered again.
9. The filter paper was removed and placed in a beaker to dry overnight. 10. The beaker was massed 24 hours later.
Data Table: Part 1 Measured melting point 92.
000 and 94. 000 Literature melting point 92. 500 Average (experimental) melting point 92. 750 Data Table: Part 2 Mass of crucible and cover 25. 017g Mass of crucible, cover and alum crystals 27. 027g Mass of alum crystals 2.
010g Mass of crucible, cover, and alum after heating #1 26. 046g Mass of water driven off . 981g Mass of anhydrous alum 1. 029g Moles of water 5. 440×10-2 moles Moles of alum 3.
985no-3moles Mole ratio of alum to water 13. 7M Data Table: Part Three . 996g Mass of filter paper only 1. 67g Mass of barium sulfate . 920g Calculations Accepted Melting Point: 92.
50 Average Melting point: 92. 000+94. 000= 186. 000 186. 000/2= 93. 000 Mass of Anhydrous Alum 26.
046g-25. 017g= 1. 029g anhydrous alum 3mole anhydrous crystal Mass and Moles of Water Driven off: 27. 027g-26. 046g= . 981g H20 driven off .
0544mol H20 driven off Accepted Mole Ratio: 12:1 Experimental Mole Ratio: = Mole ratio of anhydrous alum Mole ratio of Water 05445molH20 3. 98×1()-3mol Anhydrous Alum = 1=13. 7 Experimental Mole ratio: 13. 7:1 Percent Hydration: . 488X100= 48.
% Accepted Percent Hydration: 258. 24+216. 194=474. 46g Percent error: = 7. 02% error Mass of Barium Sulfate: = .
456gx100= 45. 6% 109. 541 g-108. 621g= . 920g of Bas04 Mass of Sulfate: Mass of 233. 40g Molar mass of S04: 96.
07g . 4116gx. 920g= . 79g of S04 Alum= . 996g sulfate Percent Error: 1- x 100= 5.
90% error In conclusion, after running three different tests on the substance in the lab it can be confirmed to be alum. The three tests that were run covered three essential properties of alum (melting point, percent hydrated, percent sulfate).
Melting point was the first test run. This test resulted in a seven percent error, and showed that by experimentation, the melting point of the alum was 92. 750. This had a few errors and a possible error may be the fact that the melting point was measured by a simple observation.
When the alum crystals started to melt, the temperature was recorded, and when all of the alum crystals were gone, a second temperature was recorded. Then the average of these two temperatures were measured and determined to be the alum’s boiling point.
Since this measurement was the result of a simple observation, it would be easy for one of the temperature to be too early, giving the experiment a boiling point that is too low. The second test had the objective of finding the alum’s percent hydration, and experimental molar ratio. Both of these measurements were found via calculations.
First, to find the percent hydration, the ass of the hydrated alum was taken, and divided the mass of the “dry’ alum (the dry alum was found by evaporating all of the water from the regular alum compound, which contains 12 moles of water naturally, then massed).
This measurement was multiplied by 100, giving the experimental percent hydration 45. 6%. Then the experimental mole ration was found to be 13. 7 to 1 instead of exactly 12. 0 to 1, the experimental hydration was 48.
8%. The resulting percent error was 7. 02%. The reason the mole ratio was over is possibly due to the crucible being massed before it was cooled adding mass because of the heat. This would force the mole ratio over the accepted 12.
There is also a chance when the alum was being heated, some of the crystals became captured in the water vapor and were carried out of the crucible.
This would have given a percent hydrate that is too high, causing a slight error. The final test run was one to determine the percent sulfate of alum. Through this test (as described in the procedure), the percent sulfate of alum was determined to 38. 1%. The accepted percent sulfate of alum is 40.
49%. This difference resulted in a 5. 90% error. Because this experiment was conducted at a high school level, the filtration rocess may result in error. Said possible errors is when the barium sulfate was filtered from the solution, some of the barium sulfate may have leaked through the filter paper.
This would result in too little sulfate, making the percent sulfate lower than if should be. Another possible error is since there was a significant time limit on the experiment; the filtering process was not completed with precaution. What is meant by that is, the beaker of the solution was not rinsed with distilled water to ensure all of the material was extracted properly. Some improvements of the lab are quite simple. First and foremost, there should be more time allotted to complete the lab if possible.
Secondly, better filtering techniques should be used. Third, the experimenters should try to perform the lab with more caution, and awareness of detail (this goes hand in hand with having more time to finish the lab). Fourth and finally, the crucible should be allowed to cool longer before being massed to prevent the mole ratio from being over the accepted 12 to 1.