CHEMISTRY 0 Hour Exam I September, 016 Dr. D. DeCoste Name Signature T.A. This exam contains 3 questions on 11 numbered pages. Check now to make sure you have a complete exam. You have two hours to complete the exam. Determine the best answer to the first 0 questions and enter these on the special answer sheet. Also, circle your responses in this exam booklet. Show all of your work and provide complete answers to questions 1, and 3. 1-0 (60 pts.) 1 (0 pts.) (0 pts) 3 (0 pts.) Total (10 pts) 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 Page No. 1 1. Caffeine is a stimulant most commonly found in coffee and is 5.19% hydrogen by mass. The molecular formula of caffeine is C x H 10 N 4 O. Determine the value of x. a) b) 4 c) 8 d) 10 e) 1. An iron (Fe) bar sits outside and rusts, forming iron(iii) oxide. Once all of the iron has rusted, the mass is 6.8 g. Determine the original mass of the iron bar. a).0 g b) 3.38 g c) 4.01 g d) 4.39 g e) 8.78 g 3. When copper (Cu) metal is dropped into an aqueous AgNO 3 solution, silver (Ag) metal is produced and the solution turns blue from the Cu + ions in solution. Determine the mass of silver that can be produced from 10.00 g of copper in an excess of silver nitrate solution. a) 10.00 g b) 16.98 g c) 33.96 g d) 48.57 g e) 67.9 g 4. Consider a reaction in which two reactants make one product (for example, consider the unbalanced A + B C). You know the following:.0 moles of A (with an excess of B) can make a maximum of.0 moles C 5.0 moles of B (with an excess of A) can make a maximum of 4.0 moles C If you react 10.0 moles of A and 10.0 moles of B, what is the maximum amount of C that can be produced? a) 8.0 mol b) 10.0 mol c) 1.0 mol d) 18.0 mol e) 0.0 mol 5. Consider mixing an aqueous solution of barium nitrate and an aqueous solution of potassium phosphate. For how many of the following cases is the concentration of the barium ion essentially equal to zero after the reaction is complete? That is, we are assuming the reaction goes to completion and does not reach equilibrium. Reacting 100.0 ml of 0.100 M barium nitrate with 100.0 ml of 0.100 M potassium phosphate. Reacting 150.0 ml of 0.100 M barium nitrate with 100.0 ml of 0.100 M potassium phosphate. Reacting 00.0 ml of 0.100 M barium nitrate with 100.0 ml of 0.100 M potassium phosphate. Reacting 00.0 ml of 0.100 M barium nitrate with 150.0 ml of 0.100 M potassium phosphate. a) 0 b) 1 c) d) 3 e) 4 6. You have a table sugar solution (sucrose, C 1 H O 11 ) sitting in an open beaker. After several days you test the solution and find that it has a concentration 33.3% higher due to evaporation. What percentage of the water must have evaporated from the sugar solution? a) 5.0% b) 33.3% c) 66.7% d) 75.0% e) The concentration of the solution will not change due to evaporation.
Hour Exam I Page No. 7. Consider the reaction between equal volumes of lead(ii) nitrate and calcium chloride in which both solutions have the same concentration in terms of molarity. How many of the following statements is/are false after the reaction is complete? Note: assume the reaction goes to completion (that is, does not reach equilibrium). The concentration of the nitrate ion is the same as the initial concentration of lead(ii) nitrate. The lead(ii) ion has all precipitated out of solution. The concentration of the chloride ion is equal to that of the nitrate ion. The only ions left in solution are the nitrate ions and the calcium ions a) 0 b) 1 c) d) 3 e) 4 8. A 4.60 g sample of cobalt (Co) metal is reacted with 156.1 ml of 1.00 M HCl(aq) to produce hydrogen gas and cobalt chloride. There is no excess reactant. Determine the formula of the cobalt chloride produced in the reaction. a) CoCl b) CoCl c) Co Cl 3 d) CoCl 3 e) CoCl 4 9. A classic chemistry lab is to determine the molar mass of a volatile (easily evaporated) liquid by vaporizing the liquid to a known pressure, temperature, and volume. Suppose you vaporize a liquid at 1.00 atm and 100.0 C in a 50.0-mL flask. The mass of the vapor is found to be 0.376 g. Which of the following could be the identity of the liquid? a) CHCl 3 b) CH 3 OH c) C 6 H 14 d) CH Cl e) C H 6 O 10. For metals that form a + charge in an ionic compound, the general equation for such a metal reacting with hydrochloric acid is M(s) + HCl(aq) MCl (aq) + H (g) 4.4 g of a metal is reacted completely with an excess of HCl and all of the hydrogen gas produced is collected in a balloon at 5 C and 1.00 atm. The volume of the balloon is measured and found to be 9.1 L. Identify the metal that was added to the HCl. a) Ni b) Mn c) Ca d) Mg e) Zn -------------------------------------------------------------------------------------------------------------------------------- 11, 1. Consider two samples He in separate container of equal volume and at equal pressure. Sample 1 has a Kelvin temperature that is 4 times that of Sample. Determine the ratio of: 11. [moles (n) in Sample 1] : [moles (n) in Sample ]. a) 1:1 b) :1 c) 1: d) 1:4 e) 4:1 1. [collision frequency (Z A ) in Sample 1] : [collision frequency (Z A ) in Sample ]. a) 1:1 b) :1 c) 1: d) 1:4 e) 4:1
Hour Exam I Page No. 3 13, 14. You have equal masses of neon gas in the left side, and helium gas in the right side, of a twobulb container connected by a valve as shown below. Initially the valve is closed. Ne He 5.0 L 1.0 L 13. After the valve is opened, what is true about the relative partial pressures of helium and neon? Assume constant temperature. a) The partial pressures of helium and neon are equal. b) The partial pressure of neon is 5.0 times as great as the partial pressure of helium. c) The partial pressure of neon is 5.0 times as great as the partial pressure of helium. d) The partial pressure of helium is 5.0 times as great as the partial pressure of neon. e) The partial pressure of helium is 5.0 times as great as the partial pressure of neon. 14. After the valve is opened, how does the final total pressure compare to the initial pressure of helium? Assume constant temperature. a) P (final) = (6/5)P (He initial) b) P (final) = (1/5)P (He initial) c) P (final) = (1/6)P (He initial) d) P (final) = (5/6)P (He initial) e) We cannot determine this without knowing the amounts of neon and helium present. --------------------------------------------------------------------------------------------------------------------------- 15, 16. Indicate which of the graphs below best represents each plot described in questions 15 and 16. Note: the graphs may be used once, more than once, or not at all. a) b) c) d) e) 15. Density (y) vs. T (K) (x) for 1 mole of an ideal gas in a rigid steel container. b 16. Pressure (y) vs. molar mass (x) for 1 mole of a given volume of a series of ideal gases at the same temperature. b
Hour Exam I Page No. 4 17. How many of the following changes will always result in shifting the equilibrium position of a gaseous chemical system? I. Changing the pressure of the system. II. Changing the volume of the system. III. Changing the temperature of the system. IV. Changing the total number of moles of gas in the system. a) 1 b) c) 3 d) 4 18. Consider the system represented by H (g) + O (g) H O(g) at equilibrium. How many of the following changes would shift the equilibrium position to the left? I. Addition of water vapor at constant volume and temperature. II. Decreasing the volume at constant temperature. III. Decreasing the temperature of the system at constant volume. IV. Addition of helium gas at constant volume and temperature. a) 0 b) 1 c) d) 3 e) 4 --------------------------------------------------------------------------------------------------------------------------- 19, 0. You have a sample of NOBr(g) in an otherwise empty, closed flask at 1.000 atm where it decomposed at constant temperature according to the following equation: NOBr(g) NO(g) + Br (g) At equilibrium, 60.0% of the original NOBr(g) has decomposed. 19. Determine the total pressure in the flask at equilibrium. a) 1.00 atm b) 1.15 atm c) 1.30 atm d) 1.50 atm e) 1.75 atm 0. Determine the value of the equilibrium constant, K p. a) 0.076 b) 0.0643 c) 0.19 d) 0.450 e) 0.675