Second practice exam for Test 1 with answers

Second practice exam for Test 1 with answers - Correct...

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Correct answers are highlighted in yellow. Part I. Each of the 12 questions in this section is worth 3 pts. (36 pts.) 1. Pentane and hexane form an ideal solution. At 25 ºC, the vapor pressures of pure pentane and hexane are 511 torr and 145 torr, respectively. A solution is prepared by mixing 1.00 moles of hexane with 2.00 moles of pentane. What is the vapor pressure of the resulting solution? A) 267 torr B) 328 torr C) 389 torr D) 656 torr E) 1167 torr 2. A sample of KNO 3 (49.0g) is completely dissolved in 101 g of water at 100 °C with precautions to avoid evaporation of any water. The solution is then cooled to 30 °C. A small amount of precipitate is observed. The solution at 30 °C is _________. A) hydrated B) placated C) saturated D) unsaturated E) supersaturated 3. At 1 atm, CO 2 concentration in water at room temperature is 3.15 x 10 -2 M . Suppose carbonated water from a bottle is opened and allowed to sit for several hours. What will the concentration of CO 2 in the carbonated water be if the partial pressure of CO 2 in the atmosphere is 3.80 x 10 -4 atm? A) 1.21 x 10 -2 M B) 3.15 x 10 -2 M C) 1.20 x 10 -5 M D) 82.9 M E) None of the other answers is correct

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2 4. Consider the reaction S 2 O 8 2- + 3I - ! 2SO 4 2- + I 3 - in aqueous solution. Initial concentrations are 0.050 M for S 2 O 8 2- and 0.072 M for I - . The reaction is followed by measuring the iodide concentration: Time / s 0 400 800 1200 1600 [I - ] / M 0.072 0.057 0.046 0.037 0.029 The average rate of disappearance of I - in the initial 400 s is (in M /s): A) 6.00 B) 3.8 5 10 - × C) 4 1.4 10 - × D) 4 2.7 10 - E) 4 3.7 10 - 5. For the reaction of problem 4 above, which of the options below represents a correct definition of the reaction rate? A) 2 28 [ ]/ d S O dt - B) 3 [ d I dt - - C) 2 4 0.5 [ d SO dt - D) 1 [ 3 d I dt - E) 3 1 [ 3 d I dt - 6. For the reaction of problem 4, the concentration of S 2 O 8 2- remaining at 1600 s (in M ) is A) 0.036 B) 0.014 C) 0.043 D) 0.064 E) 0.029
3 7. The reaction A + 2B + 3C ! X + Y is followed by the “method of initial rates” yielding the following results: Experiment Initial [A] Initial [B] Initial [C] Initial rate ( M /s) 1 0.10 0.10 0.10 2.0 x 10 -3 2 0.10 0.10 0.20 4.0 x 10 -3 3 0.20 0.10 0.20 1.6 x 10 -2 4 0.20 0.20 0.20 3.2 x 10 -2 What is the differential rate law for the reaction?

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Second practice exam for Test 1 with answers - Correct...

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