Exam 3 CH301 Mcord Sp 2009

# Exam 3 CH301 Mcord Sp 2009 - Version 260 Exam 3...

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Version 260 – Exam 3 – McCord – (53745) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Make sure you are taking the right exam. This is Dr. McCord’s AFTERNOON course that is MWF from 1-2 PM, unique 53745. McCord MWF : 1pm g = 9 . 8 m / s 2 1 atm = 101325 Pa = 760 torr R = see back of answer sheet P = ρ · g · h ( P + a ( n/V ) 2 )( V - nb ) = nRT 001 10.0 points Dissolving 3.00 g of an impure sample of cal- cium carbonate in hydrochloric acid produces 0.656 L of carbon dioxide, measured at 293 Kelvin and 1.04 atm. What is the percent by mass of the calcium carbonate in the sam- ple? (Hydrochloric acid reacts with calcium carbonate to produce calcium chloride, water, and carbon dioxide). 1. 88.2 percent 2. 54.6 percent 3. 76.3 percent 4. 94.7 percent correct 5. 64.5 percent Explanation: 002 10.0 points Two gases are contained in gas bulbs con- nected by a valve. Gas A is present in a 36 L bulb at a pressure of 273 torr. Gas B exerts a pressure of 716 torr in a 84 L bulb. What is the partial pressure of gas B after they equilibrate once the valve has been opened? 1. 603.0 2. 739.0 3. 501.0 4. 405.0 5. 550.0 6. 566.0 7. 558.0 8. 610.0 9. 522.0 10. 473.0 Correct answer: 501 torr. Explanation: V A = 36 L P A = 273 torr V B = 84 L P B = 716 torr V total = V A + V B = 120 L P B V B = P t V t P t = P B V B V t = (716 torr) (84 L) 120 L = 501 torr 003 10.0 points For a sample of gas held at constant temper- ature, a plot of volume versus pressure is a straight line. 1. False correct 2. True Explanation: Volume of a gas sample is inversely propor- tional to pressure. The plot of V versus P is not a straight line, but a hyperbola. 004 10.0 points A metal bulb is filled with 10.2 g of CHCl 3 and 1.67 g of CH 4 (two gases). What is the total pressure in the bulb if the temperature is 345 C and the volume is 50.0 mL? 1. There is no pressure because the metal bulb exerts more force than the gas does. 2. 107 atm 3. 1450 atm 4. 12,030 atm

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Version 260 – Exam 3 – McCord – (53745) 2 5. 12.1 atm 6. 0.107 atm 7. 193 atm correct Explanation: n CHCl 3 = 10 . 2 g · mol 119 . 5 g = 0 . 0854 mol n CH 4 = 1 . 67 g · mol 16 g = 0 . 104 mol n total = 0 . 1898 mol V = 50 mL = 0 . 05 L T = 345 C + 273 . 15 = 618 . 15 K Applying the ideal gas law equation, P V = n R T P = n R T V P = (0 . 1898)(0 . 08206)(618 . 15) 0 . 05 = 192 . 554 atm 005 10.0 points At 25 C and 0.5 atm, which has the highest vapor pressure in a closed 3 liter container? 1. 2.99 liters of water 2. 2 liters of water 3. 2.5 liters of water 4. They all have the same vapor pressure. correct Explanation: 006 10.0 points Which of the following gases would you pre- dict to have the largest value of the van der Waals coefficient b ? 1. C 2 F 6 2. C 2 F 2 Cl 4 3. Cl 2 4. CO 2 5. C 2 FCl 5 correct Explanation: The larger the van der Waals coefficient ‘ b ’, the larger the molecule. The largest molecules have 8 atoms. Of these, C 2 FCl 5 is larger than C 2 F 2 Cl 4 and C 2 F 6 , because Cl is larger than F. 007 10.0 points What are the main intermolecular forces found in a liquid sample of CBr 4 ?
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