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Emily Davis Partner: None Chemistry 253- TA: Alma Wellensiek Lab 3: Identifying a Constituent of “Panacetin” 9/15/2011 Purpose: The purpose of this experiment is to determine the unknown component of Panacetin. Theory: Panacetin is an analgesic (pain reducing) and antipyretic (fever reducing) drug that is sold in drug stores. However, there is a suspicion that this bottle may be counterfeit, not containing the chemicals that it should. Panacetin should be made up of about 50 percent of the unknown component that we previously separated out of Panacetin for testing.We suspect that this unknown compound is either acetanilide or phenacetin, both of which can be toxic to humans. It is very important that this component is identified so that no one unknowingly takes the “Panacetin” and becomes ill or dies.
This whole experiment is based on purifying and then finding the melting point of the unknown compound. The theory is that if a substance is pure, it will have a very specific melting point, within one or two degrees Celsius. This is in opposition to a mixed, or contaminated substance, which will have a broad melting range.Therefore, when we mix our unknown with samples of phenacetin and acetanilide, whichever mixture has a more accurate melting point will tell us what our unknown is. It is also important to make sure that the resulting melting points are close to what the proven melting points of the substances are. The lab manual tells us that acetanilide should melt at approximately 114 degrees Celsius and phenacetin should melt at around 134 degrees Celsius.
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Reaction: This experiment was based on the unknown component of “Panacetin”. In addition to our unknown, we used phenacetin, acetanilide and water.The structures of phenacetin and acetanilide are shown respectively. Phenacetin Acetanilide Solubility: Percent Yield: Total Percent Yield: Methods/ Procedures: In order to conduct this experiment, the instructions on page 59 were followed, with only a few exceptions. It was hard to tell when all of the unknown had dissolved because white flakes remained even as I kept adding hot water.
These were most likely impurities, in which case I added a bit more water than was necessary. Also, the lab manual says to take two samples of each mixture (unknown; ? phenacetin; ? cetanilide) for the melting point, but we only conducted one. There were a few safety concerns in this lab. Both phenacetin and acetanilide are known to be mild irritants, thus contact with skin and eyes should be avoided or minimized around the unknown. Another issue to keep in mind is that we will be moving glass from hot to cold surfaces, which can cause the glass to crack or break. Extra care should be taken when lowering the temperature of a beaker to avoid this issue.
Observations/ Results: When boiling the water before placing it in the unknown, my water never actually came to a boil.It was steaming very heavily and I was losing a considerable amount of water, especially from my smaller beaker, so I had to just assume that it was hot enough. This may have affected the amount of material that I got to dissolve. Either way, the fact that it took 51mL was a good indicator that my unknown was phenacetin, due to phenacetin having a much lower solubility than acetanilide. I also noticed that even though I had put in more hot water than phenacetin should have needed to dissolve (45.
9mL), white flakes still remained in the beaker.I assumed these to be impurities. Observations/ Results: As the experiment progressed, it became more and more clear that the unknown was phenacetin, starting with the fact that their solubilities were much closer.
When I was making the mixtures to put in the capillary tubes, another clue was given that the unknown was in fact phenacetin. Pure acetanilide was a brownish color, as compared to both pure phenacetin and the unknown, which were both white. After placing the capillary tubes in the MelTemp, it became clear that the unknown was phenacetin.Acetanilide, as expected, began melting far before the unknown or the phenacetin+ unknown mixture, beginning to melt at 92C and finishing at 104C. The unknown began to melt at 133C and was finished by 135C and the phenacetin and unknown mixture began melting at 134C and was totally melted by 137C. The small range and extremely close melting points give further evidence that the unknown is phenacetin. Exercises: 1.
(a) What is the minimum volume of boiling water needed to dissolve 0. 200g of phenacetin? Solubility of phenacetin in boiling water= 1. 22g/ 100mL b) About how much phenacetin will remain dissolved when the water is cooled to room temperature? Solubility of phenacetin in cold water= 0.
076g/ 100 mL (c) Calculate the maximum mass of solid (undissolved) phenacetin that can be recovered when the cooled solution is filtered. 0. 200g-0. 012g=0.
188g Phenacetin remaining 2. An unknown compound ‘X’ is one of the four compounds listed in table 3. 2. A mixture of ‘X’ with benzoic acid melts at 89C, a mixture of ‘X’ with phenyl succinate melts at 120C, and a mixture of ‘X’ with m-aminophenol melts at 102C. Give the identity of ‘X’ and explain your reasoning.Table 3.
2: Melting Points | Compound| Melting pt. , C| Benzoic acid| 121C| Phenyl succinate| 121C| m-aminophenol| 122C| ‘X’ is most likely phenyl succinate. If a substance is mixed with another chemical, it’s melting point will be lowered significantly. When ‘X’ was mixed with benzoic acid, the melting point dropped 32 degrees.
When mixed with m-aminophenol, the melting point dropped by 20 degrees. Both of these are major drops, indicating that it is neither of these substances. When ‘X’ was mixed with phenyl succinate, though, the melting point only dropped by one degree.Because of this, it is most likely that ‘X’ is phenyl succinate.
4. Tell whether each of the experimental errors in Exercise 3 will affect the melting point, and explain why. It is possible that some of the impurities in the unknown dissolved into the hot water, along with the unknown.
Also, at any time during this experiment, chemicals from other equipment such as stirring rods, beakers, spatula, etc. could have contributed contaminants to the unknown. Since any added chemicals will lower the melting point and expand the range, these potential (and pretty likely) experimental errors could have changed the melting point.