Chem123 Exam Key

Chemistry 123 Exam 1 September 15, 2005 KEY 1. CoaSbOc • X H2O is the general formula of a certain hydrate. When 43.0 g of the compound is heated to drive off the water, 26.1 g of anhydrous compound is left (CoaSbOc). Further analysis shows that the percentage composition of the anhydride is 42.4% Co, 23.0 % S, and 34.6% O. The empirical formula of the hydrate is (a) CoSO4 • 5 H2O (b) Co2SO4 • 2 H2O (c) CoSO3 • 5 H2O (d) Co2SO3 • 2 H2O (e) CoSO3 • 4 H2O 2. The explosion of nitroglycerin is described by the unbalanced equation C3H5(NO3)3 → CO2 + H2O + N2 + O2 How many moles of carbon dioxide are produced by the explosion of 9.25 × 10 of nitroglycerin? –2 mol –1 mol –2 mol (a) 9.25 × 10 (b) 2.78 × 10 (c) 3.08 × 10 –2 moles –1 (d) 5.55 × 10 mol (e) None of the above 3. Which set of values is possible? (a) (b) (c) (d) (e) Mass Number Atomic Number Number of Protons Number of Neutrons 19 235 53 32 14 42 92 131 15 7 19 92 131 15 7 23 143 79 15 8 4. When solutions of AgNO3 and Na2CO3 are mixed, solid Ag2CO3 is formed and NaNO3 remains in solution. A solution containing 12.43 g Na2CO3 is mixed with a solution containing 8.37 g AgNO3. Which of the following statements is/are not true for this reaction? I. AgNO3 is the limiting reactant. II. Na2CO3 is the limiting reactant. IV. V. This is an exchange reaction. No carbonate ion remains in solution. III. 0.0246 mol Ag2CO3 is produced. (a) II & V (b) II & IV (c) I & III (d) I, III & IV Chemistry 123 Exam 1 Harwood/Fall05 For questions 5 & 6 identify the following reactions as either: a. acid-base 5. NH4Cl (aq) 6. NaNO3(s) b. precipitation c. redox + KOH (aq) → NH3 (g) + KCl (aq) + H2O (l) + → Na (aq) + NO3– (aq) d. none of these a d 7. In the reaction below, 8.0 g of H2 react with 9.0 g of O2. Which of the following statements is true? 2 H2 + O2 → 2 H2O (a) The equation is not balanced. (b) The H2 is the limiting reactant. (c) The O2 is the limiting reactant. (d) 2.0 moles of H2O would be produced. (e) 36 grams of H2O would be produced. 8. The molar mass of lithium atom in a natural sample is 6.941 g/mol. The sample is 6 7 known to consist of Li (molar mass 6.015 g/mol) and Li (molar mass 7.016 g/mol). 6 7 What is true about the relative amounts of Li and Li in the natural sample? 6 (a) Roughly equal (a bit more Li) (b) Exactly equal 6 (c) The majority of the sample is Li 7 (d) The majority of the sample is Li 7 (e) Roughly equal (a bit more Li) 9. Identify the isotope that has atoms with 39 neutrons, 31 protons, and 31 electrons. (a) 70 Ga (b) 31 Ga (c) 70 Y 89 (d) Y (e) None of the above 10. When NaCl and KNO3 are mixed together (a) (b) (c) (d) (e) no reaction a combination reaction a displacement reaction an exchange reaction a decomposition reaction 2 occurs. Chemistry 123 Exam 1 Harwood/Fall05 2+ 11. Suppose you have a solution that might contain any or all of the following cations: Ni , + Ag , Sr 2+ 2+ and Ca . Addition of KCl solution causes a precipitate to form. After filtering off the precipitate, Na2SO4 solution is added to the resulting solution and another precipitate forms. This is filtered off and a solution of NaOH is added to the resulting solution. No precipitate is observed. Which of the 4 ions listed above must be absent from the original solution? (a) Ni 2+ + (b) Ag (c) Sr 2+ 2+ (d) Ca (e) None of them 12. Based on the activity series, which of the following reactions will occur? I. Fe (s) + H2SO4 (aq) → IV. Al (s) + Cr2O3 (s) → II. Pb (s) + MgCl2 (aq) → III. Mn (s) + HCl (aq) → V. Au (s) + AgNO3 (aq) → (a) (b) (c) (d) (e) I, III & V I & III II & V I, III & IV all will occur 13. What is the oxidation number of Cr in K2Cr2O7? (a) (b) (c) (d) (e) +2 +3 +4 +5 +6 14. In the following reaction, (a) (b) (c) (d) (e) is oxidized and I2O5 + CO → I2 + CO2 I, C O, I I, O C, O C, I 3 is reduced. Chemistry 123 Exam 1 Harwood/Fall05 For the remaining questions determine the best answer from the following list. T CaClO K PbCl2 U HF L HCl V Mg(OH)2 M HNO3 W AgCl N NaOH X NaNO3 O CaSO4 Y salt + water P NaNO2 Z salt + water + hydrogen gas Q Sr3(PO4)2 R KNO3 15. is/are ionic compounds that cannot exist. (a) (b) (c) O&P Q O (d) (e) T O&T 16. These compounds will not dissolve in water in large amounts. (a) (b) (c) V&X K&X L (d) (e) K, Q, V & W Q, V & X 17. The products of the reaction between an acid and a metal carbonate. (a) Y (b) Z (c) None of these 18. Strong acid(s). (a) (b) (c) (d) (e) L, M & U L&M L&U M&U U 19. Strong base(s). (a) (b) (c) (d) N N&V V None of these 20. A product of the reaction between sodium hydroxide and dinitrogen pentoxide. (a) M (b) N (c) P 4 (d) X