Midterm_1_S10

Midterm_1_S10 - Chem 6AL S10 Russak 19 April 2010 ...

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Unformatted text preview: Chem 6AL S10 Russak 19 April 2010 Midterm 1 The following questions are all multiple choice. Please fill out the score sheet with your name. You must put your perm number on the score sheet and fill in the bubbles associated with it to receive credit for the exam. There are equations on the back sheet that you may need to calculate your answers. You may use a calculator. There is only 1 correct choice for each question, filling in multiple answers will result in no credit given. 1. The density of mercury, the only metal to exist as a liquid at room temperature, is 13.6 g/cm3. What is that density in pounds per cubic inch? (2.54 cm = 1 in, 1kg = 2.205 lbs.) a. 849 lb/in3 b. 491 lb/in3 c. 376 lb/in3 d. 0.491 lb/in3 e. 1.83 × 10 ­3 lb/in3 2. A flask has a mass of 78.23 g when empty and 593.63 g when filled with water. When the same flask is filled with concentrated sulfuric acid, H2SO4, its mass is 1026.57 g. What is the density of concentrated sulfuric acid? (Assume water has a density of 1.00 g/cm3 at the temperature of the measurement.) a. 1.992 g/cm3 b. 1.840 g/cm3 c. 1.729 g/cm3 d. 1.598 g/cm3 e. 0.543 g/cm3 3. Potassium chloride is used as a substitute for sodium chloride for individuals with high blood pressure. Identify the limiting reactant and determine the mass of the excess reactant remaining when 7.00 g of chlorine gas reacts with 5.00 g of potassium to form potassium chloride. a. Potassium is the limiting reactant; 2.47 g of chlorine remain. b. Potassium is the limiting reactant; 7.23 g of chlorine remain. c. Chlorine is the limiting reactant; 4.64 g of potassium remain. d. Chlorine is the limiting reactant; 2.70 g of potassium remain. e. No limiting reagent: the reactants are present in the correct stoichiometric ratio. 4. What is the weight percent of glucose in a solution made by dissolving 24.6g of glucose in 145.2g of water? a. 1.5% b. 1.7% c. 14.5% d. 16.9% e. None of the above 5. How would you prepare 400g of a 2.5 wt% solution of NaCl? a. Dissolve 400g of NaCl in 2500 mL of water b. Dissolve 10 g of NaCl in 400 mL of water c. Dissolve 10 g of NaCl in 390 mL of water d. Dissolve 2.5 g of NaCl in 397.5 mL of water e. None of the above 6. A melting point was taken of a 20 mol % sample of cinnamic acid (148.16 g/mol) in urea (60.06 g/mol). What is this mixture in wt %? a. 9.2 wt % b. 12.0 wt % c. 25.1 wt % d. 38.1 wt % e. None of the above 7. Which of the following is not a colligative property a. Freezing Point Depression b. Vapor Pressure c. Boiling Point Elevation d. Osmotic Pressure e. All of the above are colligative properties 8. According to the laws of colligative properties, adding KCl to water would a. Increase the boiling point of the solution b. Decrease the boiling point of the solution c. Increase the melting point of the solution d. Both B and C e. None of the above 9. Two compounds with the same literature melting point are mixed in equal amounts. What will be the most likely outcome? a. The melting point will be the same, but the range will be broader b. The melting point will be lower and broader c. The melting point will be the same and the range will be the same d. The melting point will be lower, but the range will be sharper e. None of the above 10. What does a melting point actually represent? a. The volume required for a solid to go to a liquid b. The energy required to disrupt the crystal lattice of a solid c. The energy required for a liquid to go to a gas d. The energy required for a solid to go to a gas e. None of the above 11. The melting point of a compound is reported as a range. The range is representative of: a. The temperature when solid and the temperature when liquid b. The temperature of evidence of 1st drop and the temperature when liquid c. The temperature of evidence of shriveling and the temperature when liquid d. The temperature of evidence of meniscus and the temperature when liquid e. All of the above 12. The refractive index of diamond is 2.4. What is the speed of light through diamond? a. 1.25 m/s b. 8 E ­9 m/s c. 8 m/s d. 1.25 E8 m/s e. None of the above 13. Refractive index is reported as nD20= value. What does the D stand for? a. The D ­line of sodium b. The angle of incidence c. The angle of refraction d. The temperature that the sample was conducted e. None of the above 14. A fractional distillation, when compared to a simple distillation, will usually give: a. more volume of a more pure substance b. less volume of a more pure substance c. more volume of a less pure substance d. less volume of a less pure substance e. None of the above 15. How should cooling water be attached to a water ­jacketed reflux condenser? a. The water should flow in at the lowest point and out at the highest b. The water should flow in at the highest point and out at the lowest c. The condenser should be filled and then the water turned off so it doesn’t interfere in the experiment d. A and C e. B and C 16. You are planning on performing an experiment that calls for a starting material with at least 75% purity. You find the material on your chemical shelf, but it is a pretty dark liquid (literature says it is supposed to be clear) and there isn’t very much of it. You need as much as possible. Based on this information, what purification method would you perform? a. Perform a recrystallization b. Perform a simple distillation c. Perform a fractional distillation d. Perform a sublimation e. Any of the above would be adequate Use the graph below to answer the following questions. 17. A solution of 70/30 hexane/pentane was distilled once. What is the approximate purity of the distillate according to this graph? a. 99/1 hexane/pentane b. 70/30 pentane/hexane c. 85/15 pentane/hexane d. 90/10 hexane/pentane e. None of the above 18. According to the graph above, in order to purify a sample of 40/60 hexane/pentane one must heat until the temp of the solution is a. 42 °C b. 47 °C c. 56 °C d. 62 °C e. None of the above 19. What is true of vapor pressure? a. The higher the vapor pressure, the higher the boiling point b. Vapor pressure is not a colligative property c. The lower the vapor pressure, the lower the boiling point d. The higher the vapor pressure, the lower the boiling point e. A and B 20. Consider a 20 mol % mixture of hexane (P°=72 kPa) in toluene (P°=35 kPa). What is the combined vapor pressure? a. 7 kPa b. 14.4 kPa c. 28 kPa d. 42.4 kPa e. None of the above 21. From the question above, calculate the fraction of hexane molecules that reside in the vapor above the solution? a. 20 % b. 25% c. 34% d. 66 % e. None of the above 22. Let’s say you have an organic compound with a pKa of 5. In an organic/aqueous system, you add a base where the pKa of the conjugate acid is 3. If the organic solvent is chloroform, then where is the organic compound? a. The top organic layer b. The top aqueous layer c. The bottom organic layer d. The bottom aqueous layer e. None of the above 23. An extraction procedure specifies that an aqueous solution containing dissolved organic material be extracted twice with 10 mL portions of ether. After adding the first portion of ether, a student removes the lower layer and adds the second portion of ether. After shaking and venting, only 1 layer was visible. What did the student do wrong? a. Nothing, this is how extraction works…the phases were easily separated from one another b. The student should have taken the top layer off with a pipet and then added the second portion of ether c. The student should have allowed the organic layer to go out of the bottom of the separatory funnel and then added the second portion of ether d. The student should have allowed the aqueous layer to go out of the bottom of the separatory funnel and then added the second portion e. The student should have allowed the aqueous layer to go out of the bottom of the separatry funnel, the organic out the top, and put the aqueous back in the separatory funnel before adding the second portion. 24. Consider that you have a partition coefficient of 3 for a substance in an ether/water solution. You perform 3 extractions using ether. What is the total amount of material in the organic layer assuming equal volumes of liquids were used? a. 1.5% b. 25% c. 75% d. 98.5% e. None of the above 25. Compound-W has a partition coefficient value (K) of 2.5 in dichloromethane and water. If 1g of 44.4% 55.5% 83.3% 97% None of the above 26. A brine wash is used to remove water from organic liquids. It works by: a. Increasing the concentration of NaCl in the water later b. Decreasing the concentration of NaCl in the water layer c. Trapping water in small pockets that they cannot be removed from easily d. Forming hydrates e. None of the above compound-W is successively partitioned between CH2Cl2:H2O 2:1 v/v (volume/volume) , how much of compound-W will be in the combined CH2Cl2 layers after the second separation? a. b. c. d. e. 27. Which of the following functional groups has the lowest IR energy? a. sp3 C ­H b. sp2 C ­H c. sp C ­H d. O ­H e. N ­H 28. A stretch in the infrared was recorded to be 2.186 E ­20 Joules. What functional group does this correspond to? a. O ­H b. C ­H c. C=O d. C ­O e. None of the above Match the following structures to their Infrared Spectra: H NH2 N O OH O O O A B C D E 29. 30. 31. 32. 33. Equations: N=c/ʋ E=hc/λ h=6.626 E ­34 J.s c = 3.00 E8 m/s P=P°X P=PA+PB Υ=P/Ptotal K = [A]org / [A]aq [A]aq final / [A]aq initial = [(V2/(V2+V1K)]n pKa =  ­log Ka ...
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This note was uploaded on 08/14/2010 for the course BIO 2010 taught by Professor Le during the Summer '10 term at UCSB.

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