Melting Point - Experiment 1 - Organic Chemistry Lab | 160 311, Lab Reports of Organic Chemistry

Download Melting Point - Experiment 1 - Organic Chemistry Lab | 160 311 and more Lab Reports Organic Chemistry in PDF only on Docsity! EXPERIMENT 1 Prelab and Postlab Questions for Melting Point PRELAB QUESTIONS 1) Describe the attraction that occurs between polar molecules that increases the intermolecular attractive force. 2) Describe the attraction that occurs between molecules that can undergo hydrogen bonding. 3) How is the calibration of a thermometer carried out? (You are not carrying out this step). POSTLAB QUESTIONS 1) One of the purposes of taking a melting point is to record a physical characteristic of a new compound. Why is this important? 2) You have an unknown sample that has a melting range of 51-53°C. The three possibilities for this unknown are maleic anhydride (mp: 52-54°C), 4-nitrotoluene (mp: 54-56°C) and benzophenone (mp: 49-51°C). a) Which of the three standards can you automatically eliminate? Why? 3) What error of technique could cause a confirmed pure sample to appear to have a wide melting range when the melting point of the sample is taken? Why would this error cause the abovementioned observation? You must do the readings listed under the Lecture Schedule for this experiment and the Experiment (Lab) Schedule for this experiment. Pay special attention to how isomers and structures and intermolecular forces affect melting points, definition of eutectic point, criteria and effect of impurities on melting points, how and why determination of melting points must be done, relationship between vapor pressure of solid and liquid of a pure compound at melting point, why sample would shrink as the melting point is approached. Make sure you study your lecture notes very carefully to prepare for the quizzes (including answering any questions posed in lecture). The lecture notes, questions to ponder given in lecture and the points mentioned in the extra notes (for all experiments) are topics you have to consider for the quizzes and these as well as prelab and postlab and introduction questions are all fair game for the exam for the course. Quizzes for the course will begin during the 2nd experiment - they are given at the beginning of the lab period. You will get a take home safety quiz during the first experiment (discussed further in the last paragraph). EXPERIMENT 2 PRELAB QUESTIONS 1) Explain why propanamine (3 carbon amine) is soluble in water while heptanamine (7 carbon amine) is not. 2) The solubility of phthalic acid is water is: 0.54g/100 mL at 14°C, 18g/100 mL at 100°C. How many mL of boiling water are required to dissolve 76.0 g of phthalic acid?(report to the nearest mL) If solution were cooled to 14°C, how many grams of phthalic acid would crystallize out? (report to one decimal place) (Show calculations) 3) If you are using a trial-and-error method to pick a solvent for recrystallization, why would it be advisable to try low-boiling solvents first, especially if you have a limited sample of solid that you wish to recrystallize? 4) Describe what occurs on a molecular level when you try to dissolve one substance in another. POSTLAB QUESTIONS 1) You wish to recrystallize naphthalene (mp: 80ºC). The solubility of naphthalene in ethanol (bp: 78ºC) is 7.7g/100mL at 22ºC, in toluene (bp: 111ºC) is 28.5g/100mL at 22ºC and in tert-butylmethyl ether (bp: 55ºC) is 37g/100mL at 22ºC. Based on the data given, a) List two possible reasons why it would be inadvisable to use toluene (by itself) as a recrystallization solvent. b) If you decide to use ethanol and tert-butylmethyl ether as a solvent pair to recrystallize naphthalene, i) besides the solubility of naphthalene in each of these solvents, what criteria would ethanol and tert-butyl methyl ether have to satisfy? ii) describe which solvent you would heat up and dissolve naphthalene in initially and which solvent you would add second and at what point would you stop adding the second solvent EXPERIMENT 3 PRELAB QUESTIONS 1a) From figure 5.3 on pg. 92, what would the boiling point of a liquid mixture of 30%cyclohexane and 70% toluene be? b) If you boiled the liquid mixture of 60%cyclohexane and 40% toluene, condensed the vapor mixture it generated and then redistilled that condensed mixture, what would the vapor composition of the mixture resulting from the 2nd distillation be? 2) Calculate the mole fraction of A (XA) in the vapor if a mixture of liquids is 67%A and 33%B. The vapor pressure of pure A (P°A) is 790 torr and the vapor pressure of pure B (P°B) is 865 torr. Show calculations and give answer to 2 decimal places. 3) At pressures near that of the atmosphere at sea level, how do boiling point of most liquids change with atmospheric pressure? Following this, what do you expect the boiling point of toluene to be at 740mm mercury? 4) When does superheating occur? POSTLAB QUESTIONS 1) List two reasons why the constancy of a boiling point does not necessarily mean that the liquid only consists of one compound. 2) What observation, during a distillation, would indicate impurity in the liquid being distilled? 3) What are two advantages of using steam distillation to purify compounds? 4) You are given a mixture of two liquids, A and B, to purify. The boiling point of A is 75ºC and the boiling point of B is 84ºC. What criteria would this mixture have to satisfy for the liquids in the mixture to be sufficiently purified by simple distillation? EXPERIMENT 4 Prelab and Postlab Questions for TLC PRELAB QUESTIONS 1) What is the purpose of having very small bores on the spotters? 2) Why is it important to use a separate spotter for each of your samples? 3) You have a TLC plate that measures 9.5 cm lengthwise. You prepare it for spotting as described in the procedure, spotted samples A and B, develop the TLC plate and then visualize it. You find that the Rf for the sample A is 0.63. a) What distance did the sample A travel from the spotting line? (Report in cm to 1 decimal place) (Show calculations) b) Would sample A be more or less polar than sample B that travelled 3.7 cm on the same TLC plate? POSTLAB QUESTIONS 1) Why would uneven rising of eluent on the TLC plate lead to inaccurate results? 2) If spots are extremely close together (or right on top of each other) on a TLC plate, how can you effect their separation? 3) You can take a TLC of a solution of partially soluble material. Why does the experiment still work? EXPERIMENT 5