'Melting Point Determination Essay\r'

'Identifying an unidentified sundry(a) pile be a rocky task. In identifying a manifold, researchers lots measure some(prenominal)(prenominal) visible properties: melt spotlight, boiling diaphragm, density and observes a a few(prenominal) chemic properties: reactivity, acidity, basicity of the intensify. The priming for determining several chemical substance and physical properties of the blend is that it is quite affirm fitting for two varied compounds to wear a few physical and or chemical properties in jet; but it is highly unlikely for the two compounds to deem very many monovular physical and chemical properties (Gilber & vitamin A; Martin, 2010).\r\nThe goal of this experiment is to visualize the indistinguishability of the unnoticeable utilise the melt down- bakshis technique. If the entire compound in the list condition by your instructor had clearly varied thaw argues, it would be doable to stop the identity of the unknown by just fetching i ts warming quest. However, apiece(prenominal) of the compounds in this list has a melt down render that is close to the resolve take of an some other compound in the list. Therefore, the dissolve stain of the unknown give allow you to break downward(a) the choices to two compounds (Pavia, Lampman, & Kriza, 2013).\r\nTo determine the identity of you compound, you mustiness perform confection thawing particulars of your unknown and each of the two compounds with similar resolve blames. A diverseness melting point that is depressed and has a large-minded bunk indicates that the two compounds in the smorgasbord atomic number 18 different. It should be pointed out, however, that it is not possible to accurately teleph wizard the physical properties of newly synthesized or isolated compounds.\r\nTherefore, tables of physical properties ar only useful in identifying antecedently known compounds. However, useful information as to the compound’s identity a nd its purity can often be obtained from its melting point. Although the melting point can be used to help identify an unknown by comparing its melting point to writings values, it must be app atomic number 18nt that there atomic number 18 literally hundreds if not thousands of compounds that sh are the kindred melting point. To solve this dilemma the identity of a compound can be confirm using motley melting point method.\r\nIf you contrive a mixture of you unknown chemical and the one you suspect it whitethorn be and measure the melting point of the mixture then there are two possible results: The melting point of the mixture is the same as the tenuous compound which means that the unknown compound and the known compound are the same. The melting point of the mixture is lower than either of the two light components and the melting range is large. This is because the two compounds are different with the result that one is an impurity in the other (Dean, Jones, Holmes, & Reed, 2011).\r\nDetermination of the temperature at which the fast(a) and gas phases of a substance are in counterweight is time consuming. It is too quite difficult with a underage come up of adjudicate. Thus, in practice, most melting points are determined as capillary melting points, which can be done quickly with a small amount of sample in a capillary underpass (Bettelheim & Frederick, 2004). dissolve point analysis is a quick, relatively easy, and inexpensive preliminary exam analysis if the sample is already mostly unclouded and has a suspected identity. Additionally, analysis requires small samples only.\r\nAs with any analysis, there are certain drawbacks to melting point analysis. If the sample is not solid, melting point analysis cannot be done. Also, analysis is destructive of the sample. For soft identification analysis, there are now more than specific and accurate analyses that exist, although they are typically often more expensive. Also, samples wi th more than one solute cannot be canvas quantitatively for purity (Molavi & Barron, 2011)\r\nMethodology:\r\n finding an Identical Compound:\r\nTwo melting-point capillaries were filled with small amounts of your sample. One was used to determine an approximate melting point range for your unknown by allowing the temperature to show up at about 6oC per minute. Then the melting point apparatus was cooled to at least 5oC below the temperature at which melting began.\r\nA slow, careful determination of the melting point range was made on the scrapment sample by allowing the temperature to rise at a rate of approximately 2oC per minute. It is important that the melting point was measured carefully because finding another pupil in the testing ground with the identical compound depends on it.\r\nThe melting point range was recorded in the research testing groundoratory notebook and also on the data sheet provided by the instructor along with the savant number. From the data sheet, another scholar in the lab was located whose unknown has a melting point range that is within 4oC. A small amount of the disciple’s compound was used to prepare a sample for a mixed melting point. The error range of ±4oC was accounted for experimental error and the event that the thermometers are not calibrated thus the ranges from different instruments may vary slightly.\r\nTo prepare the mixed melting point sample, one part of the unknown condition was used to one part of the other student’s compound. The sample was mixed thoroughly by gently crushing the mixture with a fruitcake stirring rod until it looks homogeneous. The melting point range was determined and the result was recorded in the laboratory notebook.\r\nSearch was continued until you identified a student in the lab with a compound identical to yours and a second student in the lab with an unknown with approximately the same melting point range, but whose compound is not the same as yours.\r \nResults and Discussion:\r\n|Table 1 Mixed Melting localise inexplicables | |Unknown |Structure |Melting Point Range | | | |(oC) | |Benzoic Acid |[pic] |121-123 | |DL-malic Acid |[pic] |131-133 | |carbamide |[pic] |132-135 | |Trans-cinnamic Acid |[pic] |131-136 | |Succinic Acid |[pic] |184 |\r\nTable 1 shows the infractn unknowns to be identified in this experiment. The melting point range in the table was the backside of the researchers in identifying their given unknowns. Some chemical compounds given from the manual was omitted to limit the scope of the experiment. Other books give different melting point range on the compounds in the table. This is because temperature also varies in the fact that the thermometers are not calibrated.\r\nThe unknown pure compound has a white powdery solid consume. Melting point range determination is only applicable for solid compounds. Two trials were conducted to observe the melting point of the pure compound. For the first trial, it was o bserved that the compound starts to melt at exactly 135oC and the solid in the capillary pipage was completely dissolved at 137oC.\r\nThe solid melts outright because the temperature of the cooking oil used arises rapidly compared when using water as a boiling bath. The second trial was conducted to confirm if the result for trial one is precise and the finding for the melting point also ranges from 135-137oC. From the data collected, it was predicted that the unknown might be carbamide or trans-cinnamic acid. Since both urea and trans-cinnamic acid have exactly the same melting point, it is difficult to determine which one is the given compound.\r\nThe pure compound (Unknown A) was mixed to the compound (Unknown B) of one student with melting-point range of 134-136oC. both unknown have the same physical brag which fell into conclusion that the two solids are same compounds. However, the temperature of the mixed compounds decreased by 80-84oC. Possible reason for this outcome is contaminant of the mixed compound by the stirring rod used in mixing.\r\n outpouring two was conducted for the mix-melting point determination. Another student whose compound (Unknown C) has a melting point that ranges from 131-134oC was mixed with Unknown A. Both unknowns have the same physical feature with Unknown B. The unknowns were mixed thoroughly with a fresh stirring rod. The mixed compound starts to dissolve at exactly 134oC and solid in the capillary tube was completely dissolved at a temperature of 136oC.\r\nIt is reinforced evidence that the two substances are the same. According to Mayo, Pike, and Forbes (2011), the polycrystalline lattice forces holding constitutive(a) solids together are distributed over a relatively narrow zipper range. The melting points of organic compounds, therefore, are usually relatively sharp, that is, less than 2oC. The range and maximum temperature of the melting point, however, are very sensitive to impurities. Small amounts of sample contamination by soluble impurities nearly always will result in meting-point depression. The drop in melting point is usually accompanied by an elaboration of the melting-point range.\r\nThus, in addition to the melting point acting as a useful guide in identification, it also can be a peculiarly effective indication of sample purity. The effectiveness of this technique depends on the relative solubility of the substances in each other. The usefulness of mixed melting points is limited in that you must have some idea of the chemical nature of your unknown\r\ncompound and a sample of the suspected compound must be available.\r\nThe researcher used melting points to determine the purity of organic compounds. Pure compounds were seen to have a narrow melting range, while impurities were seen to cause the melting range to arrive lower and broader. From the mixture melting points the researcher definitively able to identify the unknown as trans-cinnamic acid.\r\n5. References:\r\nAl drich, S. (n.d). Retrieved July14, 2013, from LLC, Sigma-Aldrich Co, http://www.sigmaaldrich.com/catalog/ produce/aldrich/w228826?l ang=en®ion=PH\r\nBettelheim, Frederick, A., Landenberg, & Joseph M. (2004).\r\n original and Biochemistry (5th ed.). USA: A Division of Thomson Learning, Inc. Pages 17-20\r\nDean, J., Jones, M., Holmes, D., & Reed, R. (2011). possible Skills in Chemistry (11th ed.). England: Pearson Education Limimited.\r\nGilbert, J. & Martin S. (2010). data-based total Chemistry: A Miniscale and Microscale Approach: A Miniscale and Microscale Approach (5th ed.). USA: Cengage Learning\r\nMayo, D., Pike, R., & Forbes, D. (2011). Microscale primitive Laboratory with multistep and multiscale synthesis (5th ed.). United States: John Wiley & Sons, Inc.\r\nMolavi, S., & Barron, A. (2012, May 29). Melting Point Analysis. Retrieved from the Connexions web site: http://cnx.org/content/m43565/1.1/\r\nPavia, D., Lampman, G., Kriz, G., and Engel, R. (2013). A Microscal Approach to Organic Laboratory Techniques (5th ed.). USA Cencage Learning.\r\n'