Oregon State University, Summer 2009 Chemistry 121 Midterm Exam 2, July 3rd, 10 am DO NOT OPEN THIS EXAM UNTIL INSTRUCTED. CALCULATORS ARE NOT TO BE SHARED. Instructions : You should have with you several number two pencils, an eraser, your notecard, your University ID Card, and a calculator. If you have other notes with you, place them in a sealed backpack and place the backpack OUT OF SIGHT. Fill in the front page of the Scantron answer sheet with your last name, first name, middle initial, and student identification number. Leave the class section number and the test form number blank. This exam consists of 20 multiple-choice questions. Each multiple-choice question has 5 points associated with it. Select the best answer by filling in the corresponding circle on the rear page of the answer sheet. If you have any questions before the exam, please ask. If you have any questions during the exam, please raise your hand to attract the attention of a proctor. The proctor will come to you. Open and start this exam when instructed. Present your ID card when submitting the exam. Place your openended portion of this exam in the appropriate stack. You may keep the this exam, so please mark the answers you selected on it. Scoring : 20 multiple-choice questions @ 5 pts each = 100 pts Information provided 1 L = 1000 cm 3 N A = 6.022 10 23 particles/mol A periodic table, a list of polyatomic ions, solubility rules and a list of strong acids and bases, and oxidation number rules are provided on the next four sheets. Check to see that you have them. Also check to see that your exam does have 20 questions on it.
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1A 2A 3B 4B 5B 6B 7B 8B 1B 2B 3A 4A 5A 6A 7A 8A 1 2 1 H 1.00794 3 Li 6.941 4 Be 9.01218 KEY Atomic number! 1 Symbol! H Atomic mass! 1.0079 5 B 10.811 6 C 12.011 7 N 14.0067 8 O 15.9994 9 F 18.9984 2 He 4.00260 10 Ne 20.1797 3 11 Na 22.9898 12 Mg 24.3050 13 Al 26.9815 14 Si 28.0855 15 P 30.9738 16 S 32.066 17 Cl 35.4527 18 Ar 39.948 4 19 K 39.0983 20 Ca 40.078 21 Sc 44.9559 22 Ti 47.88 23 V 50.9415 24 Cr 51.9961 25 Mn 54.9381 26 Fe 55.847 27 Co 58.9332 28 Ni 58.69 29 Cu 63.546 30 Zn 65.39 31 Ga 69.723 32 Ge 72.59 33 As 74.9216 34 Se 78.96 35 Br 79.904 36 Kr 83.80 5 37 Rb 85.4678 38 Sr 87.62 39 Y 88.9059 40 Zr 91.224 41 Nb 92.9064 42 Mo 95.94 43 Tc (98) 44 Ru 101.07 45 Rh 102.906 46 Pd 106.42 47 Ag 107.868 48 Cd 112.411 49 In 114.818 50 Sn 118.710 51 Sb 121.75 52 Te 127.60 53 I 126.9045 54 Xe 131.30 6 55 Cs 132.905 56 Ba 137.327 57-71 * Rare Earths 72 Hf 178.49 73 Ta 180.948 74 W 183.85 75 Re 186.207 76 Os 190.23 77 Ir 192.22 78 Pt 195.09 79 Au 196.9665 80 Hg 200.59 81 Tl 204.37 82 Pb 207.2 82 Bi 208.9804 84 Po (209) 85 At (210) 86 Rn (222) 7 87 Fr (223) 88 Ra 226.025 89-103 ^ Actinides 104 Rf (261) 105 Ha (262) 106 Sg (263) 107 Ns (262) 108 Hs (265) 109 Mt (266) 110 (269) 111 (272) *Lanthanide Series 57 La 138.906 58 Ce 140.12 59 Pr 140.9077 60 Nd 144.24 61 Pm 145 62 Sm 150.4 63 Eu 151.96 64 Gd 157.25 65 Tb 158.9254 66 Dy 162.50 67 Ho 164.9304 68 Er 167.26 69 Tm 168.9342 70 Yb 173.04 71 Lu 174.967 ^Actinide Series 89 Ac 227.028 90 Th 232.0381 91 Pa 231.0359 92 U 238.029 93 Np 237.0482 94 Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (254) 100 Fm (257) 101 Md (258) 102 No 259 103 Lr 262
Strong Acids Strong Bases HCl, HBr, HI LiOH, NaOH, KOH HNO 3 Ca(OH) 2 (slightly soluble) HClO 4 Ba(OH) 2 H 2 SO 4 Sr(OH) 2 4
OXIDATION NUMBER RULES The oxidation number of a free element is always 0. The oxidation number of a monatomic ion equals the charge of the ion. The oxidation number of fluorine in compounds is -1. The oxidation number of hydrogen in compounds is +1. Exception: the oxidation number of hydrogen is -1 in metal hydrides, like CaH 2. The oxidation number of oxygen in compounds is -2. Exception: the oxidation number of oxygen is -1 in peroxides, like BaO 2. The oxidation number of Cl, Br, I in compounds is -1. Exception: when combined with O or F, the preceding rules apply. The oxidation numbers of all other elements in a compound adjust such that: The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. 3
1. Nitrogen forms an interesting series of oxides including N 2 O, NO, NO 2, N 2 O 4 and N 2 O 5. Which of the following statements is/are CORRECT? 1. The number of moles of N atoms in 2 moles of NO is the same as the number in 1 mole of N 2 O. 2. The number of moles of O atoms in 2 moles of N 2 O 5 is the same as the number in 5 moles of NO 2. 3. In 3 moles of N 2 O 4, there are 6 moles of N atoms and 8 moles of O atoms. 4. The oxide with the greatest (mol N/ mol O) ratio is N 2 O. 2. What are the coefficients needed to balance the following equation? a. 1, 2, 2, 1 b. 3, 2, 3, 1 c. 2, 3, 2, 1 d. 1, 3, 1, 2 e. 1, 3, 2, 3 Fe 2 O 3 (s) + CO(g) Fe(s) + CO 2 (g) 3. When the following equation is balanced, what is the ratio of the stoichiometric coefficients (b/c)? a. 3/4 b. 3/2 c. 2/1 d. 1/1 e. 2/3 a PbS(s) + b O 2 (g) c PbO(s) + d SO 2 (g) 4. Which of the following statements is INCORRECT? a. A combustion reaction is one in which a compound reacts with oxygen to make carbon monoxide and water. b. The Law of Conservation of Matter (Mass) states that the total mass of substances in a chemical reaction does not change. c. In a chemical reaction, the number of atoms of all types remains constant. d. An equation is not normally written with non-integer coefficients. e. An equation relates the number of moles of material that react and are produced. 4
5. Ammonia is produced industrially from the reaction of nitrogen and hydrogen. N 2 (g) + 3H 2 (g) 2NH 3 (g) If I wish to make 5.0 mol NH 3, how many moles of H 2 will I need? a. 1.0 mol b. 3.0 mol c. 2.0 mol d. 2.5 mol e. 1.5 mol 6. If I start with 2 mol of F 2, how many moles of SF 6 will I make by the following reaction? a. 24 mol b. 2/3 mol c. 8 mol d. 3/2 mol e. 4 mol S 8 (g) + 24 F 2 (g) 8 SF 6 (g) 7. How many grams of chromium (III) chloride (molar mass 158.6 g/mol) can I make from 5.20 g of chromium metal via the following reaction? a. 3.54 g b. 5.20 g c. 52.0 g d. 159 g e. 15.9 g Cr(s) + Cl 2 (g) CrCl 3 (s) 8. Glucose (C 6 H 12 O 6, molar mass 180.2 g) burns in oxygen to produce carbon dioxide and water. C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(g) How many grams of CO 2 are formed from 45.05 g of glucose? a. 11.0 g b. 44.0 g c. 66.0 g d. 122. g e. 264. g 5
9. Which of the answers correctly best describes the following list of compounds? Nitric acid (HNO 3 ), ammonia (NH 3 ), sucrose (C 12 H 22 O 11 ), KCl, acetic acid (CH 3 COOH) a. Strong electrolyte, weak acid, non-electrolyte, strong acid, weak electrolyte b. Strong acid, weak base, non-electrolyte, strong electrolyte, weak acid c. Non-electrolyte, strong acid, weak base, weak acid, strong electrolyte d. Non-electrolyte, strong acid, strong base, weak acid, strong electrolyte e. Weak base, weak acid, non-electrolyte, strong acid, strong electrolyte 10. Which of the following will result in an insoluble precipitate when mixed with an aqueous Pb(NO 3 ) 2 solution? a. HNO 3 (aq) b. NH 4 NO 3 (aq) c. N 2 (g) d. K 2 SO 4 (aq) e. LiClO 4 (aq) 11. Which are the spectator ions in the following reaction? a. H + and CO 3 2- b. Ni 2+ and Cl - c. Ni 2+ and CO 3 2- d. CO 2 and H + e. H + and Cl - NiCO 3 (aq) + 2 HCl(aq) NiCl 2 (aq) + H 2 O(l) + CO 2 (g) 12. Which is the correct net ionic equation for the molecular equation for the reaction between (NH 4 ) 2 S(aq) + Ni(NO 3 ) 2 (aq) NiS(s) + 2NH 4 NO 3 (aq) a. S 2- (aq) + Ni 2+ (aq) NiS(s) b. (NH 4 ) 2 S(aq) + Ni 2+ (aq) NiS(s) + 2NH 4 + (aq) c. 2NH 4 + (aq) + S 2- (aq) + Ni 2+ (aq) + 2NO 3 - (aq) NiS(s) + 2NH 4 + (aq) + 2NO 3 - (aq) d. S 2- (aq) + Ni 2+ (aq) + 2NO 3 - (aq) NiS(s) + 2NO 3 - (aq) e. Ni 2+ (aq) + 2NO 3 - (aq) NiS(s) + 2NH 4 + (aq) 6
13. Which of the following statements is INCORRECT? a. An acid is proton donor. b. Acid plus base gives a salt and water. c. The neutralization reaction between an acid and base can be written succinctly as H + (aq) + OH - (aq) H 2 O(l). d. Ammonia is a proton acceptor. e. Acetic acid is a weak acid because it dissociates 100% into acetate ions and protons. 14. What is the oxidation number of the chromium atoms in the dichromate ion, Cr 2 O 7 2-. a. +3. b. +6. c. -6. d. +7. e. +2. 15. Elemental chlorine displaces bromine from potassium bromide solution Cl 2 (g) + 2KBr (aq) Br 2 (l) + 2 KCl (aq) Which of the statements about this reaction below is CORRECT? a. Cl 2 is reduced and Br - is acting as an reducing agent. b. K + is oxidized and is acting as a reducing agent. c. Br 2 is reduced, Cl - is reduced and KBr is oxidized. d. Cl 2 is oxidized and Br - is acting as an oxidizing agent. e. This is not a redox reaction. 16. If I wish to make 125. ml of a 0.250 M solution of H 2 SO 4, how many grams of sulfuric acid should I take? The molar mass of H 2 SO 4 is 98.1 g/mol. a. 0.306 g b. 3.06 g c. 12.3 g d. 24.5 g e. 98.1 g 7
17. I take 10.0 ml of a 2.0 M NaCl solution, place it in a 500 ml volumetric flask and fill up the flask with water. What is the final concentration of the NaCl solution? a. 0.0400 M b. 0.0200 M c. 0.00400 M d. 0.100 M e. 2.00 M 18. I prepare an (NH 4 ) 2 SO 4 solution that has a concentration of 0.50 M. What are the concentrations of [NH 4 + ] and [SO 4 2- ] in this solution? a. [NH 4 + ] = 1.0 M, [SO 4 2- ] = 1.0 M b. [NH 4 + ] = 0.50 M, [SO 4 2- ] = 0.50 M c. [NH 4 + ] = 1.0 M, [SO 4 2- ] = 0.50 M d. [NH 4 + ] = 0.50 M, [SO 4 2- ] = 1.0 M e. [NH 4 + ] = 0.25 M, [SO 4 2- ] = 0.50 M 19. Which of the following statements about a titration is INCORRECT? a. The equivalence point of an acid-base titration can be detected by the choice of the correct indicator. b. A volumetric flask contains an accurate volume of liquid. c. An acid-base titration can work if you add either base to acid, or acid to base. d. A titration of the same volume of 1 M HCl and 1 M H 2 SO 4 will need the same volume of 1 M NaOH. e. Titrations can be used for redox reactions as well as acid-base reactions. 20. I perform the following acid/base neutralization titration. HCl(aq) + NaOH(aq) -------> NaCl(aq) + H 2 O(l) 25.0 ml of hydrochloric acid solution of unknown concentration required 50.0 ml of 1.00 M sodium hydroxide solution to be neutralized. What is the concentration of the acid? a. 0.50 M b. 1.00 M c. 2.00 M d. 2.50 M e. 5.00 M 8