Archives for September 2007

I. Introduction

A. Objective

The purpose of first part of this experiment is to first recrystallize impure acetanilide that is contaminated with dye methylene blue. Decolorizing charcoal will be used to purify the sample. The starting and ending weights of the acetanilide will be recorded to determine percentage of acetanilide recovered. Also, the melting points of the impure acetanilide and recrystallized acetanilide will then be determined using a Melt-Temp device. During the second part of the experiment, the melting point range of pure naphthalene will be measured using a Mel-Temp device. The will calibrate the machine, and then an unknown compound will be identified by discovering its melting range using the technique of mixture-melting points. During the final part of the experiment, the microscale recrystallization of 50 mg of impure trans-1,2-dibenzoylethylene will take place using ethanol to dilute the solvent and the Craig tube technique for recrystallization. The starting and ending weights of the trans-1,2-dibenzoylethylene will be recorded to determine percentage recovered. Also, the melting points of the impure trans-1,2-dibenzoylethylene and recrystallized trans-1,2-dibenzoylethylene will be determined using a Melt-Temp device.

B. Materials and Safety

C. Experimental Procedure

The first part of the experiment is the recrystallization of impure acetanilide. To begin, 2.5 grams of impure acetanilide will be obtained from the teacher’s assistant. Of that sample, 0.1 grams will be saved for a melting point determination. The remainder will be weighed and placed into a 250 mL Erlenmeyer flask with 50 mL of water and several boiling stones. The mixture is to be heated until the acetanilide dissolves. The heat will then be taken away and 25 mL of cold water and about 2.5 grams of decolorizing carbon pellets will be added to the mixture. The mixture will then be brought to a boil and boiled gently for one to two minutes. An additional 0.5 grams of decolorizing carbon pellets can be added if the blue color has not been completely removed. The solution should be boiled for another five minutes and this process can be repeated until the blue color is completely removed. The solution should then be filtered through a fluted filter into a warmed 125 mL Erlenmeyer flask. The original Erlenmeyer and filter paper will then be rinsed with an additional 10 mL of hot water. The 125 mL Erlenmeyer flask with the mixture is then to be cooled in an ice bath. The crystals will then be collected using vacuum filtration and a Buchner funnel. The crystals are then to air-dry on a watch glass for several days. Then the weights and melting points of the purified and impure samples will be determined using a Mel-Temp apparatus.

The second part of the experiment is melting point determination. Two melting point capillaries with samples of pure naphthalene will be tested with a Mel-Temp device to determine their melting point. An unknown will then be distributed. The unknown will be tested using the Mel-Temp device, first heating at a rate of 10-20 ºC to locate the approximate melting range, and then it will be heated at about 1-2 ºC to determine the exact melting point. To determine the identity of the unknown, the two known compounds with similar melting points will be obtained and be made into mixtures of equal amounts of unknown and known compound. The melting range of these mixtures will be determined to find the identity of the compound.

The last part of the experiment is the recrystallization of trans-1,2-dibenzoylethylene. First, a sample of 50 mg of impure trans-1,2-dibenzoylethylene is to be obtained. The sample will then be transferred to a Craig tube. Next, 0.5 mL of 95% ethanol will be added using a pipet pump and 2 mL graduated pipet along with a wood boiling stick. The mixture will be heated in a hot sand bath until the solvent begins to boil. At this time, additional ethanol will be adding dropwise until the solid completely dissolves. Then, the Craig tube is to be removed from the heat and allowed to slowly cool to room temperature. Once it is room temperature, the Craig tube will cool in an ice bath and then placed in a centrifuge to collect the crystals. The crystals are to then air dry, and the starting and ending weights are to be measured.

II. Experiment and Results

A. Data

First, a 2.443 g sample of impure acetanilide was obtained along with a second sample weighing about 0.1 g, which was later used for a melting point determination. The 2.443 g sample of impure acetanilide was placed into a 250 mL Erlenmeyer flask along with about 50 mL of water, and several boiling stones. The impure acetanilide was a greyish, brownish, flakey powder. When mixed with the water, the water turned a bright transparent blue color. This mixture was then heated in the Erlenmeyer flask on a hot plate until the acetanilide dissolved. After the acetanilide dissolved, the Erlenmeyer flask was removed from the heat and 25 mL of cold water and about 2.5 g of decolorizing carbon pellets were added to the flask. The mixture was then brought to a boil and was boiled for about 2 minutes. The mixture produced a black residue and most of the the blue color disappeared after the decolorizing pellets were added and it was brought to a boil. About an additional 0.5 g of decolorizing pellets were added and the mixture was boiled for another couple minutes to remove any more traces of blue color. The mixture was then filtered through a fluted filter in a stemless funnel into a warmed 125 mL Erlenmeyer flask. The original Erlenmeyer flask was rinsed with hot water to aid in transfering all of the mixture into the fluted filter. As the mixture was filtered, crystals began to form in the filtrate in the 125 mL Erlenmeyer flask. This flask was then put into an ice bath to cool for about 5 minutes. The acetanilide mixture was then filtered via vacuum filtration and a Buchner funnel. Transparent rectangular shaped crystals were collected in the filter paper. The acetanilide crystals collected were set aside to dry for a week. The crystals recovered were weighed and the melting point of the impure acetanilide and pure acetanilide were determined using a Mel-Temp device. The crystals recovered weighed 0.731 g. The melting point of impure acetanilide was 113 ºC and the pure acetanilide melting point was 115 ºC.

For the second part of the experiment, a sample of pure naphthalene was obtained and loaded into two cappillaries to determine its melting point using a Mel-Temp device. The temperature of the Mel-Temp was raised fairly slowly and the first trial resulted in a melting point of 81.5 ºC. The second trial resulted in a melting point of 81.0 ºC. An unknown sample labelled “4” was obtained and its melting point was determined using the Mel-Temp. During the first trial, which was the fast trial, the temperature of the Mel-Temp was raised about 10-20 ºC per minute and the unknown had a melting point of 104 ºC. During the slow trial, the temperature of the Mel-Temp was raised about 1-2 ºC per minute and the unknown had a melting point of 110.5 ºC, which was comparable to m-toluic acid and resorcinol. Two new samples were made, mixing an even amount of each known compound with unknown “4”. The melting point of these mixtures were again determined using the Mel-Temp. The melting point for the unknown mixed with m-toluic acid was 106 ºC, while the melting point for the unknown mixed with resorcinol was 110 ºC.

For the third part of the experiment, a 0.068 g sample of impure trans-1,2-dibenzoylethylene was obtained an put into a Craig tube along with 0.5 mL of 95% ethanol and a wood boiling stick. The of impure trans-1,2-dibenzoylethylene was a yellow powdery substance that when combing with the ethanol, changed the color of the liquid to a transparent yellow. The tube was heated in a hot sand bath. It was covered in sand up to the level of solution present and it was heated until the solvent began to boil. A few additional drops of 95% ethanol were added until all the solid dissolved. The Craig tube was then removed from the heat and was allowed to cool for about five mintues at room temperature and then another few mintues in an ice water bath. The Craig tube was then put into a centrifuge. The supernatant was discarded and crystals were taken out of the Craig tube and put onto filter paper using a small spatula. The crystals were yellow, thin, and long. The crystals were then allowed to dry for a week. The crystals recovered were weighed and the melting point of the impure trans-1,2-dibenzoylethylene and pure trans-1,2-dibenzoylethylene were determined using a Mel-Temp device.

III. Conclusions

I do not really know how to judge the results from the first part of the experiment. A percent recovery of 29.92% seems low to me, but that could be close to the expected recovery value. I would have to know the molecular formula of the impure acetanilide to figure out how many moles of pure acetanilide were there to begin with, then compare that to the number of moles of acetanilide recovered. I do know that there were many parts of the experiment where error could have occurred. For example, if too many decolorizing carbon pellets were added, they would have absorbed some of the acetanilide along with the impurities. If the mixture of acetanilide, water, and decolorizing pellets was not boiled long enough, there would still be left over impurities and some portion of acetanilide would still be impure and would not yield the expected amount of crystals. If the funnel and filter paper were too cold, some crystals would begin to form in the filter paper and not make it to the filtrate. The filtrate could not have been allowed to cool long enough and some crystals might not have formed. Some of the crystals could have been poured outside of the filter paper and went into the filtrate during vacuum filtration. There were many steps where error could have occurred, so it is highly unlikely to recover the actual amount of acetanilide that was present in the impure sample.

The results from the second part of the experiment seemed accurate. The melting point of the unknown was nearly identical as the melting point of the unknown mixed with resorcinal. The melting point of the unknown mixed with m-toluic acid was lower than that of pure known, which makes sense. Impurities usually make substances have lower melting points. This means the unknown was resorcinal. Error in this part of the experiment could come from using the Mel-Temp incorrectly or not evenly mixing even amounts of unknown and known samples. That could cause the temperature readings to be different.

For the third part of the experiment, error could have come from many different parts. For example, the impure trans-1,2-dibenzoylethylene could have not all dissovled during boiling. Crystals could start to form on the boiling stick before the Craig tube was centrifuged, which would have then been lost. The Craig tube could have not been cooled long enough to form all the crystals. Some crystals could have been poured off along with the supernatant after centrifugation. Some crystals were not recovered from the Craig tube because they were too hard to get out. There were many sources of potential error, so again it is highly unlikely to recover that original amount of trans-1,2-dibenzoylethylene present in the impure sample.

Abstract

A model system is a convenient way of showing what will happen in real life without going through the time and trouble of observing what happens in the wild. In this exercise, a model pond was filled with items representing variable food types to see the effect beak length has on a wading bird’s chance of survival. The model showed that a short beak meant death for a bird, and that a normal length beak (wild type) and a long beak meant survival and the production of multiple offspring for the bird in this environment.

Introduction

Natural selection is a driving force created by an environment that is exerted an individual to test its ability to survive and yield offspring (Purves, 2004). The individuals that are best suited for the environment, or most fit, will most likely succeed by living and producing offspring (Purves, 2004). The individuals that are worst suited for the environment, or least fit, will most likely die and not produce any offspring (Purves, 2004). The theory of natural selection can be represented and tested by using a model system to see what might happen in the real world. When observing what happens in real life, it could take years to gather enough data to decipher what is happening. A model system is convenient because it can predict what will happen in a short amount of time. For this lab, a model system was devised to show the effects of mutation on natural selection. A model pond was filled with items representing variable food types to see the effect a bird’s beak length has on its chance of survival.

Materials and Methods

A group containing three members was formed. Each group member was to represent an individual wading bird within a population of 100 birds. Groups were supplied with a bucket filled about two thirds of the way full with tap water and items representing three different food types. The first food floated on top of the water, the second food was suspended in the middle of the water, and the last food sunk to the bottom of the water. To represent the beak of a bird, groups were supplied with two tongue depressors rubber-banded together at one end with a screw inbetween to serve as a pivot. The first beak used was denoted as the wild type and was the standard length of the tongue depressors. Each group member individually took three 15 second trials to pick up as much food as they could with the wild type beak. Food was placed back into the bucket after every trial. The counts of food “eaten” were recorded on the data sheet.

Each group member was then randomly assigned an offspring from the wild type parents with a mutation which affected beak size. One member was assigned a short beak, which was about half the size of the standard tongue depressors. A second member was assigned a long beak, which was about the size of two standard tongue depressors. The last member was assigned the wild type beak. Three more 15 seconds trials were performed, but this time the group did the trial together to represent competition. Food was placed back in the bucket after each trial. Finally, food counts for each member were again recorded on the data sheet.

Results

In regards to the three 15 second trials with the wild type beak, the first group member averaged 11.7 total pieces (Appendix I). The second group member averaged 12 pieces of food, and the third member averaged 12.3 pieces of food (Appendix I). The group average was 12 pieces of food (Appendix I). Each member averaged 8 pieces of the food that floated at the top of the water, 3.9 pieces of the food that was suspended in the water, and 0.1 pieces of the food that sunk to the bottom (Appendix I).

In regards to the three 15 second trials when all three members competed for food, the wild type beak averaged a total of 6.3 pieces of food (Appendix I). Of those 6.3 pieces of food, the wild type beak averaged 3 pieces of the food that floated and 3.3 pieces of the food suspended in the water (Appendix I). The long beak averaged a total of 8 pieces of food (Appendix I). Of those 8 pieces of food, the long beak averaged 2 pieces of the food that floated, 4.3 pieces of the food that was suspended in the water, and 1.7 pieces of the food that sunk to the bottom. Finally, the short beak averaged 3 pieces of food (Appendix I). Of those 3 pieces, the short beak’s diet only consisted of the food that floated at the top (Appendix I). Using the guidelines for determining offspring survival provided in the lab manual, it was determined that the long beak and wild type beak both survived and produced four offspring, while the short beak died (Appendix I, Snetselaar et al., 2007).

Discussion

This experiment simulated how natural selection can affect the real world. As shown through the offspring with mutations, beak size had a great affect on their chances of survival. The most dramatic demonstration of this was the short beak. It was only able to eat the food at that floated on top of the water. When all the food was gone, there was nothing left for it to eat. This was a big disadvantage for it because the other beaks could not only eat the food that floated, but they could also eat the food that was suspended in the water and the food that sunk to the bottom. The short beak was the least fit for this environment and it was determined through calculations that it would have died.

The long beak seemed to have the biggest advantage. Our long beak was the most fit out of our three variations of beaks. The long beak had a big advantage because it was able to get all three types of food. It was the only one that could reach the food that sunk to the bottom, so once the other two types of food were all eaten, it had the remainder of the food to itself. It had no competition for the food that sunk. The long beak averaged the most amount of food per trial and it was determined through calculations that it survived and produced four offspring.

The wild-type beak also fared well in the environment. It could eat both the food that floated and the food that was suspended in the water. It could not eat the food that sunk to the bottom. While it could not eat the food that sunk, its beak was well suited for eating the other two types of food. The wild type’s beak was also well suited for the environment, and it was determined through calculations that it survived and produced four offspring.

This simulation demonstrated natural selection by showing which beak types were fittest and could survive in the environment. The short beak was least fit because it obtained the least amount of food. The lack of food led to its death. The wild type and long beak were most fit because they obtained the most food. They both survived and produced four offspring. This simulation was much like the real world where there are numerous birds with very slight variations in beak size and shape. The birds of the world find niches in the environment where their beak shape and size is best suited to feed. Mutations in beak size will either make a bird more fit or less fit. The most fit birds will have the best chance of survival and passing on their genes to their offspring, which will have beak shapes and sizes comparable to them. Over time, the alleles for less fit beaks will become less common, but changes in the environment could make the once less fit beak become a fit beak. There is constant struggle for survival, so any small change in the environment can affect which alleles are favored.

One thing we did not test in our simulation is varying the amounts of the different foods. If we were to do this, there may have been different results. For example, if there was very little of the food that floated and food that was suspended in the water, but an abundance of the food that sunk to the bottom, the long beaked bird would probably be the only bird to survive. If there was an abundance of food that floated and a normal amount of the other two foods, the short beak may have had a chance of surviving. Also, the different kinds of food could have different nutritional values, which would mean eating a lot of one type of food that is low in nutrition does not necessarily mean survival. The exercise we performed did not reveal these kinds of things, but it did show generally how mutations are affected by natural selection.

Literature Cited

Purves, William K., et al. 2004. Life: The Science of Biology (7^th Ed). (Courier Companies Inc., USA).

Snetselaar, Karen M., Jonathan Fingerut, and Joseph T. Thompson. 2007. Biology III Organismic Biology: Laboratory Manual Fall 2007. (Biology Department, Saint Joseph’s University, Philadelphia, PA).

1. What were your overall results?

The results from the test were that I am strongly left-hemisphere dominant with a balance between visual and auditory inputs. The exact results were 52.6% auditory, 47.4% visual, 61.1% left hemisphere, and 38.9% right hemisphere.

2. After reading your “Personal Evaluation”, what statements about you contained in your profile accurately fit you? Give a real example from your own life for each.

The personal evaluation stated that having a strong left hemisphere implies organization, structure, and self-monitoring, which I feel does characterize me fairly well. It also stated that it means I look at situations and problems and analyze them in a very systematic manner. This also holds true to my personality. One of my theories on life is that there are no problems, but only solutions. In any situation, I always look to see how I can get something accomplished in the best manner. One example of how I show left hemisphere dominance in everyday life is that I keep lists of things to do. I have a list for school work I need to get done, I have a list of everyday things I need to do, and I have a list of events coming up that I need to plan for. I make sure to do the first thing on the lists and cross it off before I go on to my next task.

Concerning the auditory and visual input results, I honestly do not agree with anything the personal evaluation said about my personality. The description given did not match me at all. If I were take an alternative test, then maybe the results would have been more accurate in coordinance with my sensory profile.

3. After reading your “Personal Evaluation”, what statements about you contained in your profile inaccurately fit you? Give a real example from your own life for each.

I agreed with most of what was said to come in turn with my strong left hemisphere, except the statement that everything must be a definite since improvisation is less easy for me. I feel that in the past that may have been truer, but I feel that I am a lot more spontaneous now than I have been earlier on in my life. For example, I used to have to plan every single activity I did with my friends at least a day in advance, but now I will do more things on a whim.

In regards to my sensory profile, I do not feel any of the statements given in the personal evaluation fit me. The test reported that I am balanced in auditory and visual perception, but I definitely feel that I am much more a visual than auditory person. The evaluation says that my balance of sensory preferences tends to make me more perceptive than most. I would agree that I am very perceptive visually, but auditorally it is harder for me to pick up on things. For example, in class it is much easier for me to read PowerPoint slides and take notes than it is for me to strictly listen to my teachers lecture and take notes. It is just hard for me to listen and process information at the same time. I learn a lot more by visually seeing the information.

4. Explain how you will be able to apply what you learned from this activity to your own life. That is, in what ways can you use the information learned from this activity.

I can use the information I learned to try and become better in my auditory skills. This is something I know I lack in and have been trying to improve. I know I will probably not reach the level my visual input is at, but I will make a conscious effort to improve my auditory skills. I already knew I was an analytical person, so it does not make much of a difference to me that the test reported this. I will continue to study and live my life pretty much the way I do, except I might try to be a little less structured.

5. Any other comments about your results?

I would like to take any alternate brain function tests to see if they come up with the same results this test reported because the results from this test were slightly surprising to me.