CHEMISTRY 0 Hour Exam I (Multiple Choice Section) September 8, 017 Dr. D. DeCoste Name Signature T.A. This exam contains 0 questions on 4 numbered pages. Check now to make sure you have a complete exam. Determine the best answer to these questions and enter these on the special answer sheet. Also, circle your responses in this exam booklet. Each multiple choice question is worth 3 points (total of 60 points). The free response section is worth a total of 60 points. Useful Information: Always assume ideal behavior for gases (unless explicitly told otherwise). PV = nrt R = 0.0806 Latm/molK = 8.3145 J/Kmol K = C + 73 N A = 6.0 x 10 3 υ rms = 3RT M λ = 1 ( N / V )( πd ) Z A = A V N RT πm Z = 4 V N d πrt M x = - b ± b - 4ac a Solubility Rules: 1. Most nitrate salts are soluble.. Most salts of sodium, potassium, and ammonium cations are soluble. 3. Most chloride salts are soluble. Exceptions: silver, lead(ii), and mercury(i) chloride. 4. Most sulfate salts are soluble. Exceptions: calcium, barium, and lead (II) sulfate. 5. Most hydroxide salts can be considered insoluble. Soluble ones: sodium, potassium, and calcium hydroxide. 6. Consider sulfide, carbonate, and phosphate salts to be insoluble.
Hour Exam I (Multiple Choice Section) Page No. 1 1. Tetraphenylporphyrin is composed of only C, H, and N atoms. Experiments reveal that tetraphenylporphyrin is 85.96% C and 9.1% N by mass. What is the empirical formula of tetraphenylporphyrin? a) C 7 HN 5 b) C H 15 N c) C 11 H 8 N d) C 11 H 15 N e) C 7 H 5 N. Given equal masses of each of the following, which contains the greatest mass of phosphorus? a) phosphorus pentachloride b) iron(iii) phosphide c) magnesium phosphide d) sodium phosphate e) barium phosphate 3. A 10.00-g sample of copper (Cu) sits in the air for a period of time. Since copper is a transition metal, the products can be copper(i) oxide and copper(ii) oxide. The mass of the copper oxide that has formed is 11.43 g. Which of the following best describes the product? a) The product is a mixture of copper(i) oxide and copper(ii) oxide, and there is more copper(i) oxide by mass. b) The product is a mixture of copper(i) oxide and copper(ii) oxide, and there is more copper(ii) oxide by mass. c) The product is pure copper(i) oxide. d) The product is pure copper(ii) oxide. e) The product is a 50-50% by mass mixture of copper(i) oxide and copper(ii) oxide. 4. Consider reactants, A and B, which react according to aa + bb cc, where a, b, and c are the coefficients in the balanced chemical equation. You add equal masses of A and B together and let them react. How many of the following statements are true? I. If a is greater than b in the balanced equation, and the molar mass of A is less than the molar mass of B, then A must be limiting. II. If a is greater than b in the balanced equation, and the molar mass of A is less than the molar mass of B, then B must be limiting. III. If a is less than b in the balanced equation, and the molar mass of A is greater than the molar mass of B, then A must be limiting. IV. If a is less than b in the balanced equation, and the molar mass of A is greater than the molar mass of B, then B must be limiting. a) 0 b) 1 c) d) 3 e) 4 5. A sample of lead(ii) nitrate is dissolved in water and a 0.300 M aqueous potassium chloride solution is added to the lead(ii) nitrate solution to form 3.14 g of solid. Determine the minimum volume of the potassium chloride solution required to precipitate all of the lead(ii) ions. a) 37.6 ml b) 56.5 ml c) 75.3 ml d) 113 ml e) 6 ml
Hour Exam I (Multiple Choice Section) Page No. 6. How many of the following will make a 0.400 M NaCl solution? I. Take 3.4 g of NaCl and dissolve it in 100.0 ml solution. II. Take 10.0 ml of 4.00 M NaCl and add 100.0 ml water. III. Mix 00.0 ml of 0.100 M NaCl with 600.0 ml of 0.500 M NaCl. IV. Mix 50.0 ml of 0.400 M NaOH with 50.0 ml of 0.400 M HCl. a) 0 b) 1 c) d) 3 e) 4 7. Consider mixing 150.0 ml of 0.150 M solution of calcium nitrate with 150.0 ml of a 0.150 M solution of sodium phosphate to produce a solid. Determine the concentration of the sodium ion after the precipitation is complete. a) 0.0083M b) 0.0650M c) 0.150M d) 0.1458M e) 0.1875M 8. Which of the following solutions contains the greatest number of ions? a) 400.0 ml of 1.00 M aluminum nitrate b) 500.0 ml of 1.00 M sodium sulfate c) 300.0 ml of 1.00 M iron(iii) nitrate d) 400.0 ml of 1.00 M cobalt(ii) chloride e) 400.0 ml of 1.00 M barium nitrate 9. Consider heating a 10.00 g mixture of KCl and KClO 3 to completion. When heated, KClO 3 decomposes to produce KCl and oxygen gas, while KCl is stable. After heating the 10.00 g mixture to completion, the mass of KCl is found to be 6.858 g and the oxygen gas is collected at 1.00 atm and 5 C. Determine the volume of the oxygen gas collected. a) 0.974 L b) 1.9 L c) 1.60 L d).40 L e) 4.4 L 10. Consider two 1.0-L containers. One container is a cube and the other is a sphere. Recall from geometry that these two shapes have different surface areas, and the surface area of a cube is greater than the surface area of a sphere. You add 1.00 mole of He(g) at 5 C to the cube and 1.00 mole of Ne(g) at 5 C to the sphere. Which of the following correctly describes and explains the relative pressures of the gases in each container? a) The pressure is greater in the cube. Pressure is due to the collisions of the gaseous atoms with the inside of the container. The collision frequency (Z A ) is directly proportional to the surface area (A), and since A is greater for the cube, Z A must be greater, so the pressure is greater. b) The pressure is the same in each container. Since the volume, number of moles, and temperature are the same, the total number of collisions between the gaseous atoms and container per second is the same. Because pressure is dependent on total number of collisions, the pressures therefore must be equal. c) The pressure is greater in the sphere. Since the number of moles and temperature are the same, the total number of collisions is the same. The sphere has a smaller surface area and since pressure is a force per unit area; with a smaller area, the pressure is greater. d) None of these answers (a-c) correctly describes and explains the relative pressures of the gases in the two containers.
Hour Exam I (Multiple Choice Section) Page No. 3 11. Recall during the first lecture when I inhaled SF 6 (g) and it lowered my voice. You also have probably seen someone inhale He(g) which makes the voice higher. This is in part a function of the density differences of the gases compared to the density of air. Suppose you wish to make a mixture of SF 6 (g) and He(g) so that this mixture has the same density as air (1.179 g/l) at room conditions (1.00 atm and 5 C). Determine the partial pressure of the SF 6 (g) in such a mixture. a) 0.07 atm b) 0.175 atm c) 0.50 atm d) 0.85 atm e) 0.973 atm 1. Speaking of SF 6 (g) and He(g): determine the temperature at which the effusion rate of SF 6 (g) equals that of He(g) at 5 C. a) 639 C b) 91 C c) 157 C d) 10,601 C e) 10,874 C 13. Suppose a sealed 1.00 L flask contains pure O (g) and this is completely converted to ozone [O 3 (g)] at constant temperature. Determine the ratio of the frequency of molecular collisions with the walls of the container before and after the conversion. That is: [Z A of O ] : [Z A of O 3 ]. a) 0.667 : 1 b) 0.816 : 1 c) 1. : 1 d) 1.50 : 1 e) 1.84 : 1 --------------------------------------------------------------------------------------------------------------------- 14-16. Indicate which of the graphs below best represents each plot described in questions 14, 15, and 16. Note: the graphs may be used once, more than once, or not at all. a) b) c) d) e) 14. Change in momentum (mass x velocity) per impact (y) vs. molar mass (x) for an ideal gas at constant T. 15. Mean free path (λ) (y) vs. T (K) (x) for a 1.0 mole of an ideal gas in a container fitted with a frictionless, massless piston. 16. n (y) vs. T (x) for an ideal gas at constant P and V.
Hour Exam I (Multiple Choice Section) Page No. 4 17. How many of the following statements is/are true considering chemical equilibrium? I. A system that is disturbed from an equilibrium condition responds in a manner to restore equilibrium. II. Because K is an equilibrium constant, its value for a given equation can never change. III. Adding an inert gas to a system at equilibrium cannot change the equilibrium position. IV. For a given reaction at a given temperature, there is only one set of equilibrium concentrations for the reactants and products. V. The value of the equilibrium constant at a given temperature for a given reaction mixture is the same regardless of the direction from which equilibrium is attained. a) 1 b) c) 3 d) 4 e) 5 18. Consider the decomposition of ammonia as shown below: NH 3 (g) N (g) + 3H (g) At a certain temperature, K p = 1.50 10 3. When pure ammonia is placed in an otherwise empty vessel at this temperature, equilibrium is reached after 5.00% of the ammonia has decomposed. Calculate the partial pressure of hydrogen gas at equilibrium. a) 40.83 atm b) 108.9 atm c) 1.5 atm d) 36.6 atm e) 367.5 atm 19. Consider an initial mixture N and H in which the pressure of N is.00 atm and the pressure of H is 4.00 atm. Determine the pressure of NH 3 at equilibrium (assume constant volume and temperature). These gases react according to the following equation: N (g) + 3H (g) NH 3 (g) K p = 3.14 x 10-5 a) 1.6 x 10-4 atm b).51 x 10-4 atm c) 4.31 x 10-3 atm d) 3.17 x 10 - atm e) 6.33 x 10 - atm 0. You add an excess of NaCl(s) to a beaker with 100.0 ml of water and let this sit until the system comes to equilibrium at 5 C. You carefully remove 0.0 ml of the solution without disturbing the solid NaCl on the bottom of the beaker and transfer it to a new beaker. You then add 1.000 g of solid NaCl to the solution in this new beaker at 5 C. What will happen? a) All 1.000 g of NaCl(s) will dissolve in the solution and the system will not be able to reach equilibrium. b) Some of the 1.000 g of NaCl(s) will dissolve in the solution. When the system re-reaches equilibrium, there will be less than 1.000 g of NaCl(s) remaining. c) Some of the NaCl(aq) will precipitate out of the solution. When the system re-reaches equilibrium, there will be more than 1.000 g of NaCl(s) remaining. d) 1.000 g of NaCl(s) will remain and the system will remain at equilibrium. e) 1.000 g of NaCl(s) will remain and the system will not be able to re-achieve equilibrium.