Chemistry 14CL Exam 1 Study Questions Fall 2006 Note: Distillation, which was discussed in Lecture 4 and studied in lab periods on November 2, 3 will not be tested on the midterm. It will be included on the final exam. Students with surnames beginning with A through P will take the exam in CS50; students with surnames beginning with R through Z will take the exam in CS24. You will be allowed to use your lab notebook, hand-written materials, lecture notes, and a calculator on the midterm. Review: In reviewing the experiments (8, 6, and 7a and 7b) you should think about why you used each reagent or carried out a specific procedure and what the consequences on your results would be if you had not used that reagent or carried out that procedure. In studying the theory of the techniques, review the readings in Mohrig and the texts as well as the lecture notes. Understanding, not memorization, is the key. Study questions: 1. An organic lab book gives the following solubility data for oxalic acid (HOOC-COOH; IUPAC: ethanedioic acid; MW = 90g) 9.5 g/100mL of water 23.7 g/100 mL of ethanol 16.9 g/100 mL of ether (a) A 14CL student has 45 g of oxalic acid in 1000 mL of water and wishes to extract it into an organic solvent for further experiments. Which solvent should the student use for the extraction? Explain your choice. (b) Calculate the partition coefficient for your choice. (Be sure to define the terms of your equation so the grader knows which organic solvent you are using.) (c) Calculate the weight of acid remaining in the water phase if you extracted the 40 g/1000 mL of water with 1000 mL of the solvent you chose in part (a). (d) Draw a three-dimensional representation of the most stable conformation of oxalic acid using simple lines to indicate bonds in the plane of the paper, dotted wedges to indicate any bonds going behind the paper, and dark wedges to indicate any bonds coming out of the paper. Explain why other conformations would have a higher energy. (e) The acid dissociation constants of oxalic acid are 5.36 x 10-2 and 5.3 X 10-5. Sketch the titration curve that would result from a titration of 100mL of 1.0 M oxalic acid with 1.0 M NaOH. 2. When the molecule 1-methyl-2-phenylethene (I) is drawn using the Spartan molecular modeling program, the initial strain energy is 17.5 kcal/mol. The line structure is shown below. When the structure is minimized, the strain energy drops to 5.7 kcal/mol. How does the molecule change shape to minimize the strain energy? Be specific. You may find a drawing helpful in explaining your answer.CH3HH (I) 3. Amino acids are called ampholytes. What does this mean?. (a) Write an equation for the reaction of the amino acid valine with acid. (b) Write an expression for the reaction of the amino acid lysine with base. 9. The IR spectrum of a compound, C10H18O is to be investigated. (a) How many unsaturations and/or rings are in the molecule? (b) What type of absorption(s) would you look for in the IR spectrum. Absorptions due to C=O stretch or O-H stretch; possibly C=C stretch) (c) In what region of the IR spectrum (left third, middle third, right third) would you look for this (these) absorption(s)? 10. Phenol has the structure shown below. OH List four infrared-active stretching vibrations for this molecule. Order them from 1 to 4 in terms of most energetic (1) to least energetic (4). 11. What would be the most distinct difference in the infrared spectra of (a) acetic acid and acetone (b) ethanol and ethyl amine (c) acetone and acetic acid methyl
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