1 Chem 6AL Midterm Exam Winter 2016 Name:____________________ TA: _____________________ Instructions: You may only have a pencil, a non-graphing/non-programmable calculator, and a Parscore sheet. Completely fill in each circle corresponding to your chosen answer. Use the Parscore to record your answers. On the Parscore sheet write and bubble in your perm #, and your name. There is a zero tolerance policy toward cheating. If you are caught cheating in any way (including, but not limited to, having notes or cell phone out or looking at someone else’s exam) your exam will be taken away and you will receive a zero. There are 35 questions. For true/false questions, A = True, B = False. For the three questions below, match the solvent with the correct structure. 1. Ethyl acetate E 2. Ether AD 3. Methylene chloride D 4. Which solvent is the most miscible with water? a. Hexane b. Ether c. Methylene chloride d. Acetone e. C and D are both very miscible with water 5. Some chemicals we deal with are teratogens. Which definition below is the best definition of teratogen? a. Irritates eyes b. Destroys bodily tissue c. Causes cancer d. Harms fetuses 6. True or False: Boiling stones provide heat to speed up the rate of a reaction. 7. To the side is what you observe during a miscibility test with an alcohol and water. Which alcohol did you use in your test? a. CH3(CH2)3OH b. CH3OH c. CH3(CH2)10OH d. CH3(CH2)8OH.2 8. Arrange the following molecules in order of decreasing polarity. a. 1>2>3 b. 2>1>3 c. 2>3>1 d. 3>2>1 e. 3>1>2 9. 4-Amino ethylbenzoate will be soluble in which of the following solvents? (select all that apply) a. 3M NaOH b. 3M HCl c. 3M NaCl d. Ether e. All of the above 10. Suppose you are performing a fractional distillation and liquid is just beginning to condense in the distillation head. At which spot in the distillation column does the vapor have the highest temperature? a. The top (in the distillation head) b. The bottom (right above the vapors) c. Neither (the temperature of the vapors is uniform throughout the column) Use the graph below to answer the following four questions 11. The molar composition of a mixture of compounds X and Y is 70% X and 30% Y. Use the phase diagram to estimate the composition of the vapor over this liquid. a. 90% X, 10% Y b. 75% X, 25% Y c. 25% X, 75% Y d. 10% X, 90% Y 12. If a simple distillation were performed, which component would distill first. a. X b. Y c. Simple distillation would not result in the purification of either component. 13. True or False: Y has a greater vapor pressure than X. 14. If a solution with a mole fraction of X equal to 0.9 is boiled and the vapors condensed and collected, what is boiling point of the newly collected liquid? a. 93 oC b. 80 oC c. 75 oC d. 73 oC 15. True or False: When performing the fractional distillation of the water/ethanol mixture in lab the first few drops of liquid that you collected were pure ethanol. 16. A solution is prepared consisting of 10.0 mL of acetone (FW = 58.08 g/mol, density = 0.791 g/mL, Po = 22.2 kPa) and 0.61 moles of ethyl acetate (FW = 88.10 g/mol, Po = 15.7 kPa). What is the mole fraction of acetone in the vapor above this solution? a. 0.24 b. 0.18 c. 0.29 d. 1.0 e. None of the above3 17. A student is tasked with isolating 300mg of caffeine from a 120mL tea solution. To do this the student extracts the aqueous solution three times, using 35mL of dichloromethane each time. If the partition coefficient of caffeine in dichloromethane/water is 8.1, what is the theoretical recovery amount for this extraction procedure? a. 300mg b. 292mg c. 296mg d. 267mg e. 32mg 18. You are tasked with performing an extraction of caffeine that is dissolved in 100mL of a basic aqueous solution. You have available 50 mL of ethyl acetate and 50 mL of dichloromethane. If the partition coefficient of caffeine for ethyl acetate and water is 4.5 and the partition coefficient of caffeine for dichloromethane and water is 8.1, which extraction procedure below would give the highest percent recovery of caffeine? a. Extract the aqueous solution 2 times with 25mL of ethyl acetate each time. b. Extract the aqueous solution 3 times with 16mL of ethyl acetate each time. c. Extract the aqueous solution 2 times with 25mL of dichloromethane each time. d. Extract the aqueous solution 3 times with 16mL of dichloromethane each time. e. Extract the aqueous solution once with 50mL of dichloromethane. 19. True or False: The purpose of venting during an extraction is to ensure the two layers properly mix. 20. Which is the best definition of the word ‘anhydrous”? a. Soluble in water b. Does not contain organic contaminants c. Does not contain water d. Causes genetic mutations e. Insoluble in water 21. Which of the following is not a way to resolve an emulsion during an extraction? a. Add brine b. Add a seed crystal c. Filter d. Centrifuge e. All of the above are ways to resolve an emulsion 22. What would be the result if CaOH were not added during the isolation of caffeine? a. The caffeine would not be able to leave the tea leaves, resulting in no isolation of caffeine. b. The caffeine would stay mostly in the aqueous layer and not be extracted very efficiently c. Organic acid impurities would stay mostly in the organic layer, resulting in a less pure product d. a and b e. b and c 23. Which of the following is not true of distillation? a. The larger the difference in the boiling points of two liquids, the less theoretical plates necessary to separate them. b. Azeotropic mixtures can be avoided if fractional distillation is used. c. Simple distillation works best if the two liquids have very different boiling points. d. Fractional distillation will result in a lower yield of a more pure product. e. As the number of theoretical plates increase, the amount of column hold up also increases4 24. Recrystallization is a common procedure in an organic chemistry lab. For a proper recrystallization, the impurities in your reaction should _____________ than your desired product a. be more soluble in the recrystallization solvent b. have a higher density c. have a higher Rf d. be less soluble in the recrystallization solvent e. have a lower Rf 25. Which of the following would not be useful when attempting a sublimation? a. Increasing the temperature of the sublimation apparatus. b. Placing the sublimation apparatus in