2. Print Your Name Clearly on the Exam in the Places Indicated

Practice Exam 2 CHEMISTRY Name______2012

Instructions: 1. You should have only a pencil and calculator at your desk. (Backpacks and etc at back of lab.) 2. Print your name clearly on the exam in the places indicated. 3. You may use a calculator but not a cell phone, PDA or other electronic device. 4. Turn off your cell phone.

Physical Constants Avogadro’s number NA = 6.022×1023 units/mol Planck’s Constant h = 6.626×10-34 J s Speed of light c = 3.00×108 m/s Universal gas constant R = 0.08206 L atm K-1 mol-1 Boltzmann’s constant k = 1.38066×10-23 J/K Atomic mass unit 1 amu = 1.66054×10-27 kg

Conversion Factors (Conversion factors are exact except where indicated.) 1 in = 2.54 cm °C = 59 (°F – 32) 1 mmHg = 1 torr 3.281 ft = 1 m (not exact) °F = 95 °C + 32 1 atm = 760 mmHg 1.609 km = 1 mi (not exact) K = °C + 273.15 1 atm = 760 torr 5280 ft = 1 mi 1 atm = 101 kPa (not exact) 1 atm = 14.7 lb / in2 (not exact) 1 gal = 3.785 L (not exact) 1 atm = 1.01325×105 Pa 1 cal = 4.184 J

Nomenclature 1. Name the following substance: HClO2. A. hydrochloric acid B. perchloric acid C. chloric acid D. chlorous acid E. hypochlorous acid

2. Name the compound Na2SO3. A. disodium sulfur trioxide B. sodium sulfur oxide C. sodium sulfate D. sodium sulfite E. sodium sulfide

3. What is the formula for the compound potassium hypochlorite? A. KClO4 B. KClO3 C. KClO2 D. KClO E. KCl

4. Determine the empirical formula for a compound that is 36.86% N and 63.14 % O by mass. A. NO2 B. NO3 C. N2O D. N2O3 E. NO

5. The empirical formula for a compound is CCl. The molar mass of this compound is 284.77 g/mol. What is the molecular formula of this compound? A. C2Cl2 B. C3Cl3 C. C4Cl4 D. C5Cl5 E. C6Cl6

6. Calculate the mass percent of lithium in Li3PO4. A. 26.75% B. 17.98% C. 30.72% D. 55.27% E. 20.82% Answer the next two questions about the reaction below.

Consider the following balanced reaction: 2N2O5 → 4NO2 + O2 7. How many moles of NO2 form when 2.0 moles of N2O5 react? A. 4.0 moles B. 3.0 moles C. 2.0 moles D. 1.0 moles E. 0.5 moles

8. How many moles of O2 form when 2.0 moles of N2O5 react? A. 4.0 moles B. 3.0 moles C. 2.0 moles D. 1.0 moles E. 0.5 moles

9. Calculate the number of moles of Fe and O2 that will be required to produce 4.00 mol of Fe2O3 according to the following reaction: 4Fe + 3O2 → 2Fe2O3 A. 1.00 mol Fe, 3.00 mol O2 B. 2.00 mol Fe, 2.67 mol O2 C. 6.00 mol Fe, 2.00 mol O2 D. 4.00 mol Fe, 3.00 mol O2 E. 8.00 mol Fe, 6.00 mol O2 10. How many moles of O2 are needed to completely react with 2.14 moles of C2H4. __ C2H4 + __ O2 → __ CO2 + __ H2O A. 2.14 moles B. 0.731 moles C. 6.42 moles D. 283 moles E. 1.43 moles 11. Calculate the mass of hydrochloric acid, HCl, that will be needed to react with 125 g of Al in the following reaction. (MM: Al = 26.98 g/mol; HCl = 36.46 g/mol, AlCl3 = 133.34 g/mol; H2 = 2.02 g/mol) 2Al(s) + 6HCl(g) → 2AlCl3(s) + 3H2(g) A. 169 g B. 13.9 g C. 507 g D. 56.3 g E. 1.37×104 g Practice Exam 2 Page 4 Page 4 of 8 12. Sodium azide, NaN3, decomposes according to the following equation: 2NaN3(s) → 3N2(g) + 2Na(s) How many grams of N2 are produced from the decomposition of 38.5 g of NaN3? (MM NaN3 = 65.01 g/mol; MM N2 = 28.01 g/mol) A. 24.9 g B. 59.6 g C. 16.6 g D. 11.1 g E. none of the above 13. Aluminum reacts with sulfur according to the following equation: 2Al(s) + 3S(s) → Al2S3(s) If 3.0 mol Al and 3.0 mol S are mixed, what is the theoretical yield of Al2S3 (in units of moles)? A. 0.50 mol Al2S3 B. 1.5 mol Al2S3 C. 2.5 mol Al2S3 D. 2.0 mol Al2S3 E. 1.0 mol Al2S3 14. Determine the amount of HCl formed if 60.0 g of BCl3 and 37.5 g of H2O react according to the reaction below. (MM HCl = 36.46 g/mol; MM BCl3 = 117.17 g/mol; MM H2O = 18.02 g/mol) BCl3(g) + 3H2O(l) → H3BO3(s) + 3HCl(g) A. 75.9 g B. 187 g C. 132 g D. 25.3 g E. 56.0 g 15. A sample of metallic element X, weighing 20.69 g, combines with 5.219 g of sulfur atoms, S, to form a metal sulfide with the formula X2S. Determine the atomic weight of X and use the periodic table to identify X. A. 22.99 g/mol, Na B. 39.10 g/mol, K C. 47.90 g/mol, Ti D. 52.00 g/mol, Cr E. 63.54 g/mol, Cu Answer the next four questions about the reaction below. Ammonia, NH3, reacts with molecular oxygen, O2, to form nitric oxide, NO, and water: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) (MM NH3 = 17.03 g/mol, MM O2 = 32.00 g/mol, MM NO = 30.01 g/mol, MM H2O = 18.02 g/mol) During an experiment, 105 g of NH3 and 315 g of O2 are mixed. 16. What is the limiting reactant (LR), and what is the theoretical yield of NO? A. O2 is the LR; 295 g of NO B. NH3 is the LR; 59.6 g of NO C. NH3 is the LR; 185 g of NO D. O2 is the LR; 236 g of NO E. none of the above 17. What is the theoretical yield of H2O? A. 167 g B. 354 g C. 111 g D. 177 g E. none of the above 18. How many grams of excess reagent will be left over? A. 247 g B. 68 g C. 315 g D. 210 g E. none of the above 19. If the actual yield of NO had been 91 g, what would be the percent yield of the reaction? A. 56.8% B. 38.6% C. 82.0% D. 49.2% E. none of the above 20. The percent yield of a reaction is: A. The percent of reactants (in g) that were consumed. B. The percent of the theoretical yield that was actually attained. C. The mass percent of oxygen in the products. D. The percentage of the limiting reactant (in g) that was left over after the reaction. E. (actual yield in g / amount of limiting reactant in g ) × 100% Practice Exam 2 Page 5 Page 5 of 8 Chapter 4, 5 21. Which compound, NaCl or KCl has the most negative lattice energy, and what is the reason for your choice? A. NaCl has the larger negative lattice energy because Na+ is larger than K+. B. NaCl has the larger negative lattice energy because Na+ is smaller than K+. C. KCl has the larger negative lattice energy because K+ is larger than Na+. D. KCl has the larger negative lattice energy because K+ is smaller than Na+. E. none of the above 22. Write an abbreviated electron configuration for the Co3+ ion: A. [Ar] 4s2 3d7 B. [Ar] 4s2 3d4 C. [Ar] 3d7 D. [Ar] 3d6 E. [Ar] 4s2 3d10 23. Why does sulfur form an anion with a 2- charge? A. Sulfur has two electrons in its valence shell that can be lost to make a 2- charge. B. Sulfur has four electrons in its valence shell, and needs to lose two electrons to form an octet. C. Sulfur needs two additional electrons to fill the 4s orbital. D. Sulfur is only two electrons away from having a complete outer shell of 8 electrons. E. none of the above 24. Which ONE of the following has the correct relationship between the sizes of the atoms or ions that are being compared? A. Ca < Ca2+ B. S2- > P3- C. Fe2+ < Fe3+ D. Br > Br- E. Mg2+ < Na+ 25. Which of the following isoelectronic species has the largest radius? A. Ne B. FC. Mg2+ D. N3- E. O2- 26. Arrange the following elements in order of increasing electronegativity: F, Cl, Se, S A. Se < S < Cl < F B. F < Cl < S < Se C. F < S < Cl < Se D. Se < Cl < S < F E. Se < F < Cl < S 27. Which of the following are correctly arranged in order of increasing polarity? A. Si—Cl < Si—P < Si—S < Si—F B. Si—Cl < Si—S < Si—F < Si—P C. Si—P < Si—S < Si—Cl < Si—F D. Si—F < Si—Cl < Si—S < Si—P E. Si—P < Si—Cl < Si—S < Si—F 28. Which one of the following structures represents the Lewis dot structure of NF3?

29. Which is the best Lewis structure for COCl2? Directions for NEXT FIVE Questions: use the following structure to answer these questions.

30. How many electron groups are around the central atom? A. 2 B. 3 C. 4 D. 5 E. none 31. What is the electron group shape of this structure? A. linear B. bent C. trigonal planar D. trigonal pyramidal E. tetrahedral 32. What is the molecular shape of this structure? A. linear B. bent C. trigonal planar D. trigonal pyramidal E. tetrahedral 33. What is the hybridization of the central atom? A. sp B. sp2 C. sp3 D. sp3d E. sp3d2 34. What is the bond angle observed in this molecule? A. 109.5º B. slightly less than 109.5º C. 120º D. slightly less than 120º E. 180º 35. What are the bond angles found around a molecule which is tetrahedral in shape? A. 120° B. 180° C. 90° D. 109.5° E. none of the above

36. Which of the following best represents the Lewis dot structure of calcium iodide? 37. Use formal charges to decide which one of the following structures is the more stable resonance structure for the molecule CO2.

A B C D E O C O O C O O C O O C O all are equally stable 38. What is the molecular shape around a central atom that has two single bonds and two lone pairs connected to it? A. linear B. trigonal planar C. tetrahedral D. trigonal pyramidal E. bent 39. Which of the following compounds is polar? A. CS2 B. SF2 C. BeCl2 D. XeF2 E. all are nonpolar 40. Which ONE of the following molecules has a trigonal planar molecular geometry? A. NF3 B. BeF2 C. O3 D. BF3 E. H2O

Which one of the following compounds has a square planar molecular shape? A. CF4 B. NF4 + C. SF4 D. XeF4 E. BrF3 42. In valence bond theory, a double bond is composed of: A. two sigma bonds B. a sigma bond and a pi bond C. two pi bonds D. a sigma bond and a delta bond E. a delta bond and an epsilon bond Chapter 6 43. Natural gas, or methane, is an important fuel. Combustion of one mole of methane releases 802.3 kilojoules of energy. How much energy does that represent in kilocalories? A. 3.36×103 kcal B. 3.357 kcal C. 191.8 kcal D. 0.192 kcal E. 1.918×105 kcal 44. Which ONE of the following statements is NOT true? A. The change in enthalpy for exothermic chemical reactions is negative. B. In an exothermic reaction, the products are higher in energy than the reactants. C. An endothermic reaction is one in which energy is absorbed by the system from the surroundings. D. If ΔH° is positive in the forward direction, it will be negative in the reverse direction. E. If the coefficients in a balanced reaction are multiplied by 2, the enthalpy change for the reaction is multiplied by 2. 45. Which ONE of the following thermochemical equations has a value of ΔH° that corresponds to the enthalpy of formation, ΔHf°? A. 6C(s) + 6H(g) → C6H6(l) B. ½N2(g) + O2(g) → NO2(g) C. N2(g) + 3H2(g) → 2NH3(g) D. H2O(l) + ½O2(g) → H2O2(l) E. 2H(g) + O(g) → H2O(l) 46. Calculate the energy change for the following reaction, using the enthalpies of formation provided. SO2Cl2(l) + 2H2O(l) → 2HCl(g) + H2SO4(l) A. -105.2 kJ B. -32.9 kJ C. -1176.1 kJ D. +613.4 kJ E. -1586.2 kJ

47. Which one of the following is NOT an endothermic process? A. ice melting B. boiling soup C. water evaporating D. condensation of water vapor E. dry ice subliming 48. The reaction shown below is ______and therefore heat is ______by the reaction. 4Al(s) + 3O2(g) → 2Al2O3(s); ΔHº = -3351 kJ A. endothermic, released B. exothermic, absorbed C. endothermic, absorbed D. exothermic, released E. none of the above 49. Use Hess’s law to derive the enthalpy of the following reaction: N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(l) Use the following thermochemical equations: N2H4(l) + O2(g) → N2(g) + 2H2O(l) ΔH = -597.0 kJ H2(g) + ½O2(g) → H2O(l) ΔH = -285.8 kJ H2(g) + O2(g) → H2O2(l) ΔH = -187.8 kJ A. -1070.6 kJ B. -123.4 kJ C. -1364 kJ D. -793.0 kJ E. -489.8 kJ

Practice Exam 2 Page 8 Page 8 of 8 50. What is the enthalpy change (ΔH°) for the reaction 4NaCl(s) → 4Na(s) + 2Cl2(g), if the reaction 2Na(s) + Cl2(g) → 2NaCl(s) has ΔH° = - 821.8 kJ? A. +1644 kJ B. +410.9 kJ C. -1644 kJ D. -410.9 kJ E. -205.5 kJ 51. When aluminum oxide, Al2O3, is heated to high temperatures, it decomposes to produce aluminum metal by the following thermochemical equation: 2Al2O3(s) → 4Al(s) + 3O2(g); ΔH° = +3352 kJ In order to produce 75.0 g of aluminum, how much heat energy will be required? A. 9320 kJ B. 2330 kJ C. 1210 kJ D. 37300 kJ E. none of the above 52. Which ONE of the following thermochemical equations has a value of ΔH° that corresponds to the enthalpy of formation, ΔHf°? A. 2H(g) + O(g) → H2O(l) B. 6C(s) + 6H(g) → C6H6(l) C. N(g) + 2O(g) → NO2(g) D. NO(l) + ½O2(g) → NO2(g) E. 1/2N2(g) + 3/2H2(g) → NH3(g) 53. Acetylene burns in air according to the following equation: 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g); ΔH° = -2511.6 kJ Given that ΔHf° of O2(g) is 0 kJ, ΔHf° of CO2(g) is -393.5 kJ, and ΔHf° of H2O(g) is -241.8 kJ, what is ΔHf° of C2H2(g)? A. 454 kJ B. 227 kJ C. -454 kJ D. -227 kJ E. none of the above 54. In the thermite reaction, powdered aluminum reacts with iron(III) oxide to produce iron metal and aluminum oxide: 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s); ΔH° = -852 kJ When this reaction is carried out, 1250 kJ of heat energy are released. How many grams of iron are also formed? A. 81.95 g B. 2.974×104 g C. 163.9 g D. 327.8 g E. 9531 g