Organic Chemistry Laboratory I--Lab 3, Fall 2018.ppt -...

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Unformatted text preview: Laboratory 3: Physical Properties II and Identification of an Unknown Organic Liquid Physical Properties II and Identification of an Unknown Organic Liquid Index of Refraction Identification of Organic Liquids by Physical Properties: Density, Refractive Index, Boiling Point Determining the Composition of a Mixture Technique E: Index of Refraction Exercise E.1 Measuring the Refractive Index of an Unknown Liquid Questions 1, 3, 4, 5 on page 34— read 32-34 first Index of Refraction Refraction Definition of index of refraction: n = sin i sin r An important physical property of organic liquids found in chemical reference books Correction factor must be used if n is measured at temperatures other than 20oC: nD20 = nobs + 0.00045 (t – 20) Index of Refraction The Abbe Refractometer Refraction in Abbe Refractometer Cross section of part of the optical path of an Abbe refractometer. The sample thickness has been exaggerated for clarity. Optical Field in Refractometer Refractive Index Scale Exercise E.1: Measuring the Refractive Index of an Unknown Liquid Place 4 drops of unknown pure liquid between the plates of an Abbe refractometer. Measure and record the refractive index. Record the ambient temperature and apply correction factor if necessary. Record corrected refractive index. Using Table 1E-1 (page 34) identify the unknown liquid. Calculate the percent error between the corrected value and the literature value. Repeat for three unknown liquids. Exercise E.1 Data for Three Unknown Liquids For example: Unknown pure liquid refractive index was observed to be 1.4209 measured at 25oC. – Calculation of the corrected refractive index – Pick the most likely compound from table 1E-1 – Calculation of the Percent Error Experiment 3.2: Identification of Organic Liquids by Physical Properties Measure the density of a pure liquid and then consult Table 1B-1 (page 22) Measure the refractive index of a pure liquid and then consult Table 3.2.1 (page 191) Determine the boiling point of a pure liquid and then consult Table 3.2.1 (page 191) Apply correction factors for temperature and for barometric pressure Calculate percent error of each of the measured physical properties Questions 2, 3 on page 190—read page 189 first Calculation of Percent Error % error = literature value – experimental value x 100 literature value Experiment 3.2 Data Unknown pure liquid: 0.5 ml weighs 0.4046 g 102.4oC boiling point 1.4008 refractive index at 25oC Determining the Composition of a Liquid Mixture Determine the refractive index of Unknowns A and B; determine most likely identity of A and B Determine the refractive index of a mixture of A and B Assuming that the relationship between refractive index and concentration is linear, calculate the composition of the mixture (that is, ?%A and ?%B) Before Laboratory 3 Read each section of textbook for Technique E and Experiment 3.2 As you go through the reading, type into computer, upload Pre-Lab Report to Black Board course website, print out and place into lab notebook, so you have the following during lab: 1. Your name and name of lab partner 2. Title of experiment 3. Date the experiment was performed 4. Abstract (1-4 will be on the cover page of the lab report.) 5. Reference sections in textbook 6. Reactions that may occur during experiment (not applicable to this lab) 7. Chemicals to be used (not applicable to this lab, since they are unknowns) 8. Flow scheme (not applicable to this lab) 9. List of experimental procedures for each technique and experiment) (be as detailed as possible) (third person past tense) 10. Answers to assigned questions (for Technique E and Experiment 3.2) During Laboratory 3 Enter all procedural information, data, and observations while performing techniques and experiments in lab Write legibly in black ink; if a mistake is made, cross out and correct Have lab notebook initialed by instructor at end of experiment (before leaving lab) After Laboratory 3 After the lab, put information already in computer into final form, so it reflects what you actually did in lab (make corrections on computer) To prepare a lab report, add the following additional information to the information already in your computer. The objective is to have a stand alone (3 or 4 or more page) report to turn in at the beginning of the next lab. Additional information needed to complete a lab report: 11. Data and observations during lab (actual measurements for density, refractive index and boiling point) 12. Data analysis (calculations of corrected measurements) 13. Results (Exercise E.1—identity of the three unknown liquids; Experiment 3.2—see 1-5 on page 191; Identity of two compounds in the mixture and their percent composition) 14. Conclusions (validity of the results, utility of techniques, sources of error) 15. References (in addition to textbook) 16. Spectra (not applicable to this lab) 17. Carbon copy of pages used in laboratory notebook for notes ...
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  • Fall '19
  • Index of Refraction, refractive index, Test method

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