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UL Lafayette CHEM 107 - Final Exam - CHEM 107

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CHEM 107 (Fall-2007) Final Exam (105 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 (54 pts: 18 @ 3 pts each). Circle the ONE best answer: 1. Which of the following molecules is classified as predominantly ionic? a) SO3 b) OCl2 d) P2S5 d) NaN3 2. Which of the following species have linear molecular shape? I) SO2 II) OF2 III) NO2+ IV) XeF2 a) III and IV b) only IV c) I and III d) I and II 3. Which of the following ions is expected to be paramagnetic? a) Zn2+ b) O2- c) Cu+ d) Co2+ 4. Calculate the wavelength, in meters, of microwave radiation that corresponds to an energy of 2.63 J/mol photons. a) 2.63 b) 4.55 x 10-2 c) 1.14 x 108 d) none of the above 5. The ground state electron configuration of tantalum, Ta (Z = 73) is a) [Xe] 5d3 6s2 b) [Xe] 4f14 5d3 6s2 c) [Xe] 4f14 6d3 6s2 d) [Xe] 4f14 5d5 6. Aluminum and oxygen react according to the following equation: 4 Al (s) + 3 O2 (g) 2 Al2O3 (s) What mass of Al2O3, in grams, can be made by reacting 4.6 g of Al with excess oxygen? a) 35 b) 17 c) 1.2 d) 8.7 7. If a gold ring has a mass of 5.50 g in temperature from 25.0 to 28.0 ºC, how much heat is absorbed? (specific heat of gold is 0.129 J/g ºC) a) 2.1 J b) -2.1 J c) 0.24 J d) 130 J 18. Which name is incorrect? a) Mg3P2: magnesium phosphide b) Cr2(SO4)3: chromium(III) sulfate c) S2F2: disulfur difluoride d) TiO2: titanium dioxide 9. Calculate ∆H° for the following reaction using the given enthalpies of formation. 2 NO (g) + 5 O2 (g) 2 NO2 (g) ∆Hf° NO (g) = 90.25 kJ/mol & ∆Hf° NO2 (g) = 33.18 kJ/mol a. +57.07 kJ b) -57.02 kJ c) -114.14 d) +114.14 kJ 10. Two aqueous solutions of AgNO3 and NaCl are mixed. Which of the following diagrams best represents the mixture? 11. What is the best description of Einstein’s explanation of the photoelectric effect? a) Electrons have a definite mass. b) Light consists of particles with a definite energy. c) Ejection of photons occurs when the intensity of light increases beyond a certain minimum. d) Ejection of electrons occurs when the energy of the photon is greater than a certain minimum. 12. Which of the following molecules is expected to be polar? a) BeF2 b) CO2 c) XeF4 d) NF3 13. Which of the following has the greatest first ionization energy? a) Br b) Sn c) Se d) Kr 14. The greatest deviation from the Ideal Gas Law is expected at: a) high T, high P b) high T, low P c) low T, high P d) low T, low P 15. To what speed, in meters per second, must neutrons be accelerated to have an associated wavelength of 174 pm? (mass of neutron = 1.675 x 10-27 kg) a) 2.27 x 103 a) 2.27 x 106 c) 2.2 x 109 d) 2.27 216. How many non-bonding electron pairs are there around the central atom in the Lewis structure of SeF4? a) 1 b) 2 c) 3 d) 4 17. If gallium, atomic number 31, combines with selenium, atomic number 34, what is the most likely formula based on your knowledge of the periodic nature of the elements? a) Ga2Se3 b) GaSe2 c) Ga2Se d) GaSe 18. Which of the following species would have the largest radius? a) P3- b) S2- c) K+ d) N3- Part II. (9 pts) Bonding and molecular structure 1. For N2O molecule (laughing gas, NNO): a) Draw the Lewis structure of the molecule as well as the resonance structures (draw all if there is any) b) number σ and π bonds c) bond angle d) the molecular shape of the molecule a) Lewis Structure & resonance (if there is any) b) # of σ bonds -------- # of π bonds --------- c) Bond angle --------------------- d) Molecular shape -------------------- 3Part III. Calculations (42 pts: 6 @ 7 pts) Show all work for full credit. Please express all answers with the proper units and correct number of significant figures. 1. When heated, lithium reacts with nitrogen to form lithium nitride: 6 Li (s) + N2 (s) 2 Li3N (s) If 12.3 g of Li are heated with 33.6 g of N2: a) Determine the limiting reactant then b) What is the theoretical yield of the reaction? c) If 5.89 g of Li3N is formed. What is the percent yield of the reaction? a) Limiting reactant b) Theoretical yield 20.6 g c) Percent yield 28.6% 42. A piece of sodium metal undergoes complete reaction with water as follows: 2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g) The hydrogen gas generated was collected over water at 25.0 °C and 1.00 atm. The volume of the wet gas is 246 mL. Calculate the number of grams of sodium used in the reaction. The vapor pressure of H2O at 25°C is 23.79 mmHg. Mass of Na = 3. Calculate the standard heat of formation of carbon disulfide, CS2 from its elements {C (graphite) + 2 S (rhombic) CS2 (l)}, given that: C (graphite) + O2 (g) CO2 (g) ∆H°rxn = -393.5 kJ S (rhombic) + O2 (g) SO2 (g) ∆H°rxn = -296.4 kJ CS2 (l) + 3 O2 (g) CO2 (g) + 2 SO2 (g) ∆H°rxn = -1073.6 kJ ∆H°f (CS2, l) = 54. Vitamin C is essential for prevention of scurvy (and large doses may be effective in preventing colds). Combustion of a 0.2000-g sample of this carbon-hydrogen-oxygen compound yields 0.2998 g CO2 and 0.0819 g H2O. What is the empirical formula of vitamin C? In another experiment, the molar mass of the vitamin was found to be about 178 g/mol. What is the molecular formula of vitamin C? 6 5. Milk of magnesia is an aqueous suspension of magnesium hydroxide, Mg(OH)2 used to treat acid indigestion. Calculate the volume of a 0.035 M HCl solution (a typical acid concentration in an upset stomach) needed to react with two spoonfuls of milk of magnesia (approximately 10.0 mL, at 0.080 g


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