CHEM 107 (Fall-2007) Exam 2 (104 pts) Name: ------------------------------------------------------------------------, Clid # ------------------------------- LAST NAME, First (Circle the alphabet segment of your LAST NAME): A-C D-H I-L M-R S-Z Please answer the following questions: Part I: Multiple Choices (56 pts: 13 @ 4 pts each + 4 pts bonus). Circle the ONE best answer: 1. Which of the following species is a weak acid in water? a) HNO2 b) NH3 (aq) c) HCl d) HNO3 2. Which of the following equations DO NOT represent an oxidation? a) CrO42-Cr3+ b) SO2 SO3 c) Zn Zn2+ c) 2 I- I2 (l) 3. The oxidation states of sulfur in F3SN and S2O32- are: a) +6 and +4, respectively b) +6 and +2, respectively c) -6 and +2, respectively d) 0 and -2, respectively 4. For the reaction: Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g), the spectator ion(s) are: a) Zn2+ and SO42- b) only SO42- c) SO42- and H+ d) Zn2+ and H+ 5. In the above problem, the redox reaction is classified as: a) decomposition reaction b) combination reaction c) displacement reaction d) combustion reaction 6 . In the reaction: CaCO3 (s) + 2 HCl (aq) CaCl2 (aq) + H2O (aq) + CO2 (g) What volume of 6.0 M HCl will be needed to react with 0.350 mol of CaCO3? a) 1.17 L b) 42.0 mL c) 117 mL d) 583 mL 7. Aluminum and oxygen react according to the following equation: 4 Al (s) + 3 O2 (g) 2 Al2O3 (s) What mass of Al2O3 (102.0 g/mol), in grams, can be made by reacting 2.70 g of Al with excess O2? a) 10.2 g b) 20.4 g c) 1.28 g d) 5.10 g 128. Which of the following salts are expected to be insoluble in water? a) (NH4)3PO4 b) MgI2 c) K2S d) SrSO4 9. What is the mass of KOH in grams that need to neutralize 280.0 mL of 0.600 M HNO3 solution? a) 9.43 b) 0.168 c) 168 d) no answer was given 10. How many molecules of hydrogen sulfide, H2S are contained in 0.50 L of H2S at 1 atm and 27 ˚C? a) 1.34 x 1022 b) 1.22 x 1022 c) 3.00 x 1022 d) 2.03 x 10-2 11. Given a sample of a gas at 27.0 ˚C, at what temperature would the volume of the gas be doubled, the pressure remaining constant. a) 54.0 ˚C b) 13.5 ˚C c) 327 K d) 327 ˚C 12. Assuming ideal gas behavior. Which of the following statements is INCORRECT? a) The pressure of the gas results from the collisions of the gas molecules with the wall of the container. b) The volume occupied by a gas depends on its temperature, pressure and number of moles. c) When the temperature of a gas sample is increased at constant pressure, the density of the gas will also increase. d) In a mixture containing H2 and O2 molecules, the H2 molecules, on the average are moving faster than the O2 molecules. 13. 10. The concentration of cholesterol (C27H46O) in normal blood is approximately 0.005 M. How many grams of cholesterol are in 750 mL of blood? a) 3.75 b) 9.70 x 10-3 c) 1.93 d) 1.45 14. Which of the following would cause a reduction in the volume of a gas? a) Increasing the number of molecules (constant P& T). b) Decreasing the pressure (constant n & T) c) Decreasing the temperature (constant n & P) d) Increasing the kinetic energy (constant n & P) Part II. Equations and formulas (12 pts) In the following section please include the physical states as (s, l, g aq) for reactants and products. Use the periodic chart for charges on each ion and reference sheet. Please write N. R. if there is no reaction. 1. (4 pts) Write the balanced chemical equation for the reaction, if any occurs between aqueous solutions of Mg(NO3)2 and Na2CO3 (write N.R. if they do not react; no chemical equation)Chemical equation: 2. (8 pts) Write the balanced chemical equation and the net ionic equation for the reaction between aqueous solutions of Na2S and ZnCl2, and then identify the spectator ion(s) 3 Chemical equation: Net ionic equation: Spectator ion(s): Part III. Calculations (36 pts) Show all work for full credit. Please express all answers with the proper units and correct number of significant figures. 1. (16 pts) A chemist mixes 80.0 g of manganese(IV) oxide with 100.0 g hydrochloric acid under conditions for the following reaction: MnO2 (s) + 4 HCl (aq) MnCl2 (s) + Cl2 (g) + 2 H2O (l) a) Which reagent will be totally consumed (limiting reactant)? b) What is the maximum number of grams of Cl2 that can be produced? a) Limiting reagent: b) Max. mass of Cl2 = c) What is the percent yield of the reaction, if 44.7 g of Cl2 is produced? b) % yield =2. (10 pts) Sodium azide, NaN3 (65.0 g/mol), the explosive compound in automobile air bags, decomposes according to the equation: 2 NaN3 (s) 2 Na (s) + 3 N2 (g) What mass of NaN3 (65.0 g/mol) is required to provide the nitrogen needed to inflate a 25.0 L bag to produce a pressure of 988 mmHg at 25 ºC? Mass of NaN3 = 3. (10 pts) The reaction of a copper penny with nitric acid results in the formation of a red-brown gaseous compound containing nitrogen and oxygen. A sample of the gas at a pressure of 727 mmHg and a temperature of 18 ºC weighs 0.289 g in a flask with a volume of 157.0 mL. Calculate the molar mass of the gas, and suggest a reasonable chemical formula for the compound (NO, NO2, N2O, N2O5, N2O4). b) M = 45.9 g/mol, NO2 4Exam 2 – Fall 2007 You will have 60 minutes to complete this exam. The exam has 4 pages plus the Periodic Table and Reference page. When you are told to do so, tear off the Periodic Table cover sheet and use as required during the exam. 1 1 H 1.01 Periodic Table of the Elements 2 He 4.00 2 3 Li 6.94 4 Be 9.01 5 B 10.816 C 12.01 7 N 14.01 8 O 16.00 9 F 19.0010 Ne 20.18 3 11 Na 22.99 12 Mg 24.30 13 Al 26.9814 Si 28.08 15 P 30.97 16 S 32.06 17 Cl 35.4518 Ar 39.95 4 19 K 39.1 20 Ca 40.08 21 Sc 44.96 22 Ti 47.88 23 V 50.94 24 Cr 52.00 25 Mn54.9426 Fe 55.8527 Co 58.9328 Ni 58.6929 Cu