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2nd_exam_1 - St John’s University Department of Chemistry...

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Unformatted text preview: St. John’s University Department of Chemistry Course: Chemistry 1120 ' Summer Session H Second Examination July 24, 2000 NAME - I.D. # INSTRUCTIONS 1. Write your name'and I.D. # on this page, and on the answer (Scantron) sheet. ' 2. USe the examination pages and the blank scrap page to work out your answers. 3. For each of the 25 questions, indicate the correct answer on the Scantron with a #2 pencil. Each question is worth FOUR points. A non programmable, non graphic calculator may be uSed for this exam. ‘1 ’ Answers will be posted on the notice board Opposite to Room 324, St. Albert Hall. 4. Hand in the examination questions, scrap page, and the Scantron sheet. ‘ 5. You will have 75 MINUTES to complete the exam. PROPER CONDUCT DURING EXAMINATIONS: 1. Communication between students by any means is prohibited. 2 H Possession Of any unauthOrized papers is prohibitedf V ,, 3. No paging devices or cell phonesallowed. 4. All books, papers, and jackets should be placed in the fiont of the room. 5. Violation of any of the above rules will result in a grade of zero. CONVERSION FACTORS , l kilogram = 2.204 pounds Avog'adro’s N0. = 6.02 x 1023 R = 0.0821 L atm mol'l K'1 R = 8.314 J mol'1 K'1 1 mol gas = 22.4 L gas at ‘STP Density Ong = 173.57 g mL‘I Speed oflight = 3.00 x 108 m/s Kw = 1.0 x 10-14 Sp Heat H20 = 40184 J/goC Planck’s Constant = 6.63 x 10'34 J/s 1cal=4.l84J , 1mi1e=1.609km . A PERIODIC TABLE & A FORMULA SHEET ARE ATTACHED 1. When a solute such as ammonium sulfate, (NH4)ZSO4, is dissolved in a solvent like water one of the observed effect is: ‘ VA. A decrease in the vapor pressure of the solvent. B. A decrease in the boiling point of the liquid. ' C. An increase in the melting point of the liquid. D; An‘increase in the vapor pressure of the solute. 2. At room temperature the vapor pressure of acetonitrile, CH3 CN, is 81.0 torr, while that of acetone, C3H60, is 184.5 torr. What is the vapor pressure of a solution which contains 0.550 moles of acetonitrile and 0.350 moles of acetone ? Assume ideal behavior. ' A. 109 torr B. 130 torr v6. 121 torr ' D- 144 torr 3. For a chemical reaction, AH > 0 while AS < 0 . Which of the following is correct ? V“ The reaction must be non-spontaneous regardless of temperature, and becomes even more so at higher temperatures. B. The reaction must be spontaneous regardless of temperature, and becomes even more so at lower temperatures. C. The reaction may or may not be spontaneous, but spontaneity is favored by low temperatures rather then by high temperatures. D. The reaction may or may not be spontaneous, but spontaneity is favored by high temperatures rather then by low temperatures. 4. 7. What is the freezing point of a solution that cantains 36.0 g of glucose, C6H1206’ in 750.0 g of water ? Kf= 1.86 oC/m. A. -0.267 00 v1! ' -0.496 0c c. -0.186°C‘ D. -1.03 00 An aqueous solution of a protein with a concentration of 15.0 g/L at 35.0 0C, had an osmotic pressure of 0.160 torr. What is the molecular mass of the protein ?. A. 1.51 x 106 ‘21. 1.80 x106 0. 2.0x 103 D. 1.6 x 109 Wax is a solid mixture of hydrocarbon compounds consisting of molecules with long chains of carbon atoms. WhiCh solvent below wouldyou expect to be most capable of dissolving wax ?‘ A. Water, H20 B. Methanol, CH3 OH C. Ethylene glycol, HO-CHz-CHZ—OH 11D. Heptane, CH3-CH2-CH2-CH2-CH2-CH2-CH3 Which of the following is a concentration unit whose value will be altered if the temperature of anaqueous solution is increased ? 1 . . , . 1 , .. A. Mole fiaction A. Molarity C. Molality D. Weight percent 8. 10. ll. 12. What forces enable ionic compounds to dissolve in water ? A. Hydrogen bonding B. Ion-ion forces C. Dipole-dipole forces VK Ion-dipole forCes A solution is made by mixing 138.2 g of ethanol, C2H6O, 103.6 g of water, and 80.11 g of methanol, CH4O. What is the mole fraction of methanol in the mixture ? A. 10.4886 v37 0.2223 C. 0.2663 D. 0.51 14 A solution of potassium hydroxide is prepared by mixing 3.55 g of KOH with 25.0 g ofwater. What is the percent by mass of KOH in this solution ? .A. 12.4% ~ ‘B. 14.2%- C. 26.6 % D. 87.6 % Which one of the following aqueous solutions will have the lowest freezing point temperature ? A. > 0.200mMg(NO3)2 ’ B. 0.200 mMgSO3 C. 0.300 m KBrO3 fl. 0.300 m CaC12 A gas occupies 2.5 L in an apparatus that exerts a pressure of 3.6 atm. The pressure is reduces to halfof its initial-value and the gas is allowed to expanchssuming‘ that. . temperature is constant, calculate the P-V work of this system in Liters-atmospheres. 13. The reaction of a substance A with substance C was carefully studied under conditions where the [C] remainedconstant. The graphs of [A] vs time, and that of ln[A] vs time both gave curves, but the graph of 1/ [A] vs time gave a'straight line. Which of the following is correct ? The reaction is zero order with respect to A The reaction is first order with respect to A The reaction is Second order with respect to A p.806? The reaction is third order with respect to A 14. The half-life of a radioactive substance is 14 days. How much of a 500 mg sample will remain alter 28 days 7 A. 250 mg ‘ ‘13. 125 mg C. 62.5 mg D. 500 mg 15. A chemical reaction has been observedto g9 tocompletion in 2.50 hours at 30 0C. How long will this reaction take at 20 0C 7 A. 1.25 hours B. 1.67 hours J. 5.00 hours D. 25.0 hours 16. 17. 18. The solubility of oxygen in water is 0.00380 g/L when the temperature is 25.0 0C and the partial pressure of gaseous Oxygen is 760 torr. The oxygen gas above the water is replaced by air at the same temperature and pressure, in which the mole traction of oxygen is 0.210. What should be the solubility of oxygen in water under these new conditions ?' A. 1.05 x 10'6 g/L a! 7.98 x 10-4 g/L c. 1.33 x 10-3 g/L ‘ D. 0.606 g/L Which of the following would have no efi'ect on the rate of a reaction taking place in the liquid phase ? A. Concentration B. Temperature C. Inhibitor V6. l’ressure i A reaction has the rate law, Rate = k[X]2[Y]3. What is the overall order of the reaction ? A. l 0 c4 ’5 19. 20. 21. For the reaction , 2 M + 2 N V 2 P + Q, some studies on how the initial rate of the reaction varied with Concentration were carried our. Some data are given below- Expt. # [M] [N] Rate (moi/Ls) 1 0.100 0.100 0.000230 2 0.100 0.200 0.000920 3 0.200 0.200 0.000920 The rate law is therefore: .43. Rate = k[N]2 B. Rate = k[M] [N]2 C. Rate = k[M][N] D. Rate = k[M]2 In a first order reaction with only onereagent, the reaction was started with a concentration of reactant equal to 0.0800 M. After exactly 2 hours, the concentration had fallen to 0.0400 M. What is the concentration alter exactly 3 hours ? A. 0.0300M vfi. 0.0283M C. 0.0340 M D. 00276 M The rate constant for a first order decomposition reaction is 0.01 11' min”1 . What is the half—life of the reaction ? A. 111 min B. 31.25min J6. 62.4 min D. 27.1 min 22. Of the species listed below, which one has the highest standard entropy value (So) ? A. (CH3)2CO (1) ' «é. VC4H10(g) 0. H200) D. He(g) 23. The criterion for a spontaneous chemical reaction is A. AS = 0 - B. AE < 0 ' C. AH>0 V195. AG<O 24. Which one of the following processes is accompanied by a decrease in the-entropy of the system ‘2 A. The mixing of 1 liter of water with one liter of ethylene glycol to procude ‘2 liters of antifi'eeze solution. ' ‘ B. The crushing of an antacid tablet into the powdered form. C. The thawing of the fioiéfi orange juice concentrate Which Was left in the car. “5. The absorption of odorous gaseous compounds by the charcoal filter in your home central air cleaning unit. _ 25. Real solution often show positive deviations fiom Raoult’s Law because: /. ‘ Attractions between solute and solvent particles are weaker than solute-solute .. . .. and solvent-solvent attractions. B. All attractive forces are identical in solute and solvent. C. Attractions between solute and solvent particles are identical to the solvent- solvent attractions, but weaker than solute-solute attractions. D. The heat of solution (AHsoln), is negative. ...
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