Popular in Organic Chemistry Lab 1
Popular in Department
This 6 page Study Guide was uploaded by Gabriela Montalvo on Friday December 4, 2015. The Study Guide belongs to chm at University of Miami taught by Lab TA in Fall 2015. Since its upload, it has received 12 views.
Reviews for Lab 1
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 12/04/15
Gabriela Montalvo CHM 205 Atul Parab September 14, 2015 Experiment 1: Recrystallization Lab 0 Questions: 1. The melting point range can be defined as the temperature point at which the substance starts melting till the temperature point at which it is in a liquid state. 2. The correct heating range is about 1°C2°C/ min; if any faster then the point that the substance starts to melt might be missed. 3. a. The sample began to burn in the first trial due to too high of a setting; this could be reported as an experimental error due to not using the proper rate. b. If the sample disappears from the tube then that illustrates that either it was not tightly packed or too little sample was used; more sample can be added to correct this during the test. 4. Ferrocene and Acetlyferrocene: 172.5°C and 81°C83°C Adipic Acid and Citric Acid: 153°C and 152°C 5. The compounds could be mixed with pure Adipic Acid leading to one being fairly similar and the other melting much faster. If you have two varying acids then they will melt at a much lower temperature whereas if you have two of the same acids the melting temperature will stay the same. 6. The equivalent of 0.8 mL of chloroform is approximately 22 drops. a. First find the density of methanol and convert the mass(g) to volume(mL); take that much volume into a calibrated pipette. b. Then put the drops in a beaker that is tarred in order to get the mass; the volume is known due to 1 mL being the equivalent of 28 drops. Lab 1 Questions: 1. The minimum of ethanol needed is 14.3 mL and the amount of compound X is 0.3 g. 2. If too much hot solvent is used then part of the sample may be lost due to it becoming part of the solution and then not filtering out completely due to the high temperature. This may lead to less percent yield of pure crystal formation. Also, the crystals may not dry fast enough due to there being too much liquid in the filtrate. 3. The filtrate solution would be shocked therefore causing immediate crystal formation. This would lead to the formation of crystals on the actual filter and the crystals found in the filtrate would not be as pure due too fast formation. 4. The solvent should have a lower boiling point than the melting point of the substance. In this case the benzyl alcohol was a much higher boiling point than the melting point of fluorenol, which it is the solvent for. Such a higher temperature will not permit for the structure of fluorenol to form because it will denature the organic compound therefore not allowing crystals to form. 5. a. Hot gravity filtration will take out the sand because it will get caught in the filter since it is not part of the actual solution and is actually in solid form. b. The addition of charcoal removes the colored organic compounds because the conjugated pi bonds in the compound are attracted to the carbon in the charcoal. c. The overall process of recrystallization would have to be repeated in order to filter out the very soluble contaminant; this happens when the crystals start to form. 6. Acetone is highly polar which helps dissolve most organic compounds. Due to its low boiling point recrystallization is not as successful because evaporation would occur soon after heating. But acetone shows evidence of aiding in ignition therefore not being completely safe for lab usage. Lab 1: Recrystallization (Unknown #2) Introduction: Recrystallization is an essential technique used to obtain pure compounds. The basic principle for purifying a solid includes thoroughly dissolving the impure compound in a hot solvent, filtering the solution in the case of any insoluble impurities, gradually chilling the solution to manipulate crystal formation, filtration of the crystalline compound, and drying of the crystals. I . Purpose: The purpose of this experimentation is to identify the unknown solid with the use of the technique recrystallization. This process aids in the removal of the impurities in an unknown solid. The process of recrystallization can be performed on both large and small scales, and includes the same basic procedure described above. Once a proper solvent has been selected, the aforementioned procedure is employed with the addition of weighing the crystalline compound, and measuring the melting points of the sample. For a microscale recrystallization, smaller filtration flasks, Craig tubes, and a centrifuge should be employed. Upon recrystallization the solution is transferred to the Craig tube, and then inverted and placed in a centrifuge to separate the solvent from the crystals. II . Data: A. Macrorecrystallization Mass of Unknown 0.501g Mass of Crystals (±.001 g) 0.206 g Melting point fast 121.4°C – 124.2°C Melting point slow 121 °C – 122.3°C Percent Yield 41.1% Mixed Melting Point A: Benzoic Acid 121°C 122°C Mixed Melting Point B: Benzamide 123°C127°C B. Microrecrystallization: Mass of Unknown 0.077 g Mass of Crystals (±.001 g) 0.068 g Melting Point Range 120°C 122°C Percent of Yield 88.3% Boiling Water Added 28 drops/ 1mL C. Identification of Solution: Benzoic Acid III. Observations: A. Part A ● Actual Mass of Unknown Sample: 0.501 g ● No color was present in filtrate therefore charcoal was completely filtered out ● Kept filtrate in ice bath for ten minutes B. Part B ● Actual Mass of Unknown Sample: 0.075 g ● Filter pipette was warmed prior to the hot gravity filtration by pipetting near boiling water through the filter so that the filtrate is not shocked and the crystals form slower and more pure. ● The particles began to crystalize while the test tube was in the near boiling molecule. IV . Results: The process of recrystallization has yielded the ultimate result of the identification of the unknown sample #2 as Benzoic Acid. The melting point range obtained was very similar to that of Benzoic Acid with ranges of 121.4°C – 124.2°C and 120°C 122°C; the textbook melting point range for Benzoic Acid is 121°C 122°C. V . Discussion: During the procedure, there were many chances of error due to human and machine error. To start off, a possibility for error is during the heating of the deionized water in the macrorecrystallization process. Rather than heating it to a near boiling point, the water was a little cooler. This could have been one reason for why not all the particles in the test tube from the unknown sample were dissolved. Therefore, there was a lower percent yield of the crystals to the actual mass of the sample; not all the crystals were able to form due to some particles not fully dissolving. Another source of error may have occurred while finding the melting point. According to literature, the correct procedure to obtain an accurate and precise melting point is to do two rounds of finding the melting point; for the first time a rough estimate of a range is found while the setting of the machine is at “5, but the second time around is supposed to be much slower. Now that the general melting point is known, during the second time the temperature should only increase about 1°C per minute after reaching 110°C. In order to do this, the setting on the MelTemp© machine should be placed to “1”. Such a procedure provides for more accurate results because the temperature is being so closely observed. But during the actual experimentation, the melting point was only found once and was done at the setting of “5” , therefore not allowing for accurate viewing of the thermometer. The lack of precision may have led to inaccurate results. The unknown sample #2 was then identified as benzoic acid by comparing the percent yields and melting points achieved from both the macrorecrystallization and microrecrystallizaton. VI . Conclusion: The overall experiment was partially successful due to the melting points and the percent yields achieved. While the melting points for both of the procedures were within 1°C of each other, the percent yields were not as close. The percent yield for the macrorecrystallization was approximately 47.2% less than the percent yield for the microrecrystallization. Since the percent yields are not as close, the data shows signs of inaccuracy. This illustrates that either some crystals were lost in Part A or there were still some impurities in Part B. But the melting points of both the crystals were very similar; also the ranges of the melting points were fairly small which signifies a very pure crystal sample. Therefore this shows that the probability of the unknown sample # 2 being Benzoic Acid is fairly high.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'