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DR. THOMAS J. GREENBOWE FALL 2006 THIS EXAM CONSISTS OF 21 QUESTIONS ON 6 PAGES PARTS Part I Page 2 Part II Pages 3 & 4 Part III Page 4 Page 5 TOTAL GRADING POINTS 24 pts 24 pts 22 pts 30 pts 100 pts ________ SCORE ________ ________ ________

CHEM 177 HOUR EXAM II OCTOBER 2, 2006

NAME______________________ RECIT. INSTR._______________ RECIT. SECT.________________

NOTE: THE METHOD YOU USE IN SOLVING QUESTIONS MUST BE CLEARLY SHOWN IF YOU ARE TO RECEIVE FULL CREDIT. QUESTIONS ARE WRITTEN ON BOTH SIDES OF EACH PAGE. TABLE. THE LAST PAGE CONTAINS USEFUL INFORMATION AND A PERIODIC THIS SHOULD BE REMOVED AND USED FOR ADDITIONAL REFERENCE AND SCRATCH PAPER. DO NOT PUT ANSWERS ON THE TEAR AWAY PAGE.

Teaching Assistants and Recitation Sections Name Sections Time Ram Adhikary 23, 25 10:00, 12:10 Tanya Gupta 11 8:00 Wei Huang 10, 19 4:10, 2:10 Susan Lorge 2, 29 9:00, 10:00 Tim Mauldin 4, 17 12:10, 1:10 Sean Nedd 8, 15 2:10, 10:00 Kerry Riley 5, 30 12:10, 11:00 Sean Riley 3, 12 11:00, 9:00 Robert Roggers 13, 16 9:00, 11:00 Salil Sabnis 14, 22 10:00, 8:00 Suzanne Sander 24, 26 12:10, 2:10 Heather Spangler 7, 9 1:10, 3:10 Laine Stewart 6, 20 1:10, 4:10 Ben Tang 21, 28 5:10, 4:10 Ka King Yan 18, 27 2:10, 3:10 Chad Yuen 1 8:00

THE ANSWER KEY TO THIS EXAM WILL BE POSTED ON BULLETIN BOARD #5 IN THE HALLWAY EAST OF ROOM 1002 GILMAN AND ON THE CHEM 177 WEBSITE. CHEM 177 FINAL EXAM MONDAY, DECEMBER 11 4:30-6:30 P.M.

2 PART I ­ Multiple Choice. (8 questions at 3 pts each = 24 pts total) 1. A weak electrolyte exists predominately as _____ in solution. a) atoms 2. b) ions c) molecules d) electrons e) an isotope

Which of the following are strong electrolytes? 1) HCl a) 1, 4 b) 1, 3, 4 2) HC2H3O2 3) NH3 4) KCl d) 1, 2, 4 e) 2, 4 c) 1, 2, 3, 4

3.

Which ion(s) is/are spectator ions in the formation of a precipitate of AgBr via combining aqueous solutions of CoBr2 and AgNO3? a) Co2+ and NO3­ b) NO3­ and Br ­ c) Co2+ and Ag+ d) Br ­ e) NO3­

4.

The balanced net ionic equation for precipitation of CaCO3 when aqueous solutions of Li2CO3 and CaCl2 are mixed is a) 2 Li+(aq) + CO32­(aq) Li2CO3(aq) b) 2 Li+(aq) + 2 Cl­(aq) 2 LiCl(aq) c) Li+(aq) + Cl­(aq) LiCl(aq) d) Ca2+(aq) + CO32­(aq) CaCO3(s) e) Li2CO3(aq) + CaCl2(aq) 2 LiCl(aq) + CaCO3(s)

5.

Which of the following are strong acids? 1) HI a) 3, 4 b) 1, 2, 3, 4 2) HNO3 3) HF 4) HBr d) 2, 3, 4 e) 1, 2, 4 c) 1, 3, 4

6.

Silver chloride has a similar structure to sodium chloride but does not dissolve in water. One reason for this might be that a) b) c) d) e) the ions are too large to dissolve. the ions are too small to dissolve. the melting point of the salt is too high. the attractions between the ions are too strong for water molecules to separate them. some ions are too light for gravity to pull them down.

7.

The combustion of propane (C3H8) in the presence of excess oxygen yields CO2 and H2O. C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(g) When 2.5 mol of O2 are consumed in the reaction, _____ mol of CO2 are produced. a) 1.5 b) 3.0 c) 5.0 d) 6.0 e) 2.5

8.

Calculate the oxidation number of the chlorine in perchloric acid, HClO4, a strong oxidizing agent. a) ­1 b) +4 c) +5 d) +7 e) none of the above is the correct oxidation number

3 PART II ­ Multiple Choice. (6 questions at 4 pts each = 24 pts total) 9. Sulfur and oxygen react in a combination reaction to produce sulfur trioxide, an environmental pollutant: 2 S + 3 O2 2 SO3 In a particular experiment, the reaction of 1.00 g S with 1.00 g O2 produced 0.80 g of SO3 (molar mass = 80.07). The % yield in this experiment is a) 30 b) 296 c) 21 d) 88 e) 48

10.

The following diagrams represent the reaction of A2 (shaded spheres) with B2 unshaded spheres). Identify the limiting reactant and write a balanced equation for the reaction. a) b) c) d) A2 is the limiting reactant; A + 3 B AB3. A2 is the limiting reactant; A2 + 3 B2 2 AB3. B2 is the limiting reactant; A + 3 B AB3. B2 is the limiting reactant; A2 + 3 B2 2 AB3.

11.

What is the molarity (M) of an aqueous solution containing 22.5 g of sucrose (C12H22O11) (molar mass = 342) in 35.5 mL of solution? a) 0.0657 b) 1.85 × 10­3 c) 1.85 d) 3.52 e) 0.104

12.

What is the concentration (M) of an aqueous methanol solution produced when 0.200 L of a 2.00 M solution was diluted to 0.800 L? a) 0.800 b) 0.200 c) 0.500 d) 0.400 e) 8.00

13.

Which picture below correctly shows the orientation of water molecules around a positively charged ion in solution? (Unshaded spheres represent hydrogen atoms, shaded spheres represent oxygen atoms, gray sphere represents a positive charged ion.)

a)

b)

c)

d)

e)

4 14. The following pictures represent aqueous solutions of three acids HX, HY, or HZ, with water molecules omitted for clarity. Unshaded spheres represent hydrogen atoms or ions and shaded spheres represent X, Y, or Z atoms or ions. Which of the three is the strongest acid, and which is the weakest?

HX

a) b) c) d)

HY

HZ

HX is the strongest acid and HY is the weakest acid. HY is the strongest acid and HX is the weakest acid. HY is the strongest acid and HZ is the weakest acid. HZ is the strongest acid and HY is the weakest acid.

PART III ­ Problems. Show all work. Answers should include appropriate units and contain the correct number of significant figures. (52 pts total) 15. (8 pts) A compound that is composed of carbon, hydrogen, and oxygen contains 70.60% C, 5.90% H, and 23.50% O by mass. The molecular weight of the compound is 136 amu. What is the molecular formula? a) C8H8O2 b) C8H4O c) C4H4O d) C9H12O e) C5H6O2

16.

(6 pts) What is the concentration (M) of sodium ions in 4.57 L of a 0.847 M Na3P solution? a) 0.847 b) 3.87 c) 0.185 d) 2.54 e) 0.282

17.

(8 pts) A 36.3 mL aliquot of 0.0529 M H2SO4(aq) is to be titrated with 0.0411 M NaOH(aq). What volume (mL) of base will it take to reach the equivalence point? (All of the acid is neutralized.) H2SO4(aq) + 2 NaOH(aq) Na2SO4(aq) + 2 H2O(l) a) 93.6 b) 46.8 c) 187 d) 1.92 e) 3.84

5 18. (2 pts) Problem #18 is the bonus question. This is the only optional problem on the exam. A solution is prepared by adding 1.60 g of solid NaCl to 50.0 mL of 0.100 M CaCl2. What is the molarity of chloride ion in the final solution? Assume that the volume of the final solution is 50.0 mL. a) 0.747 b) 0.647 c) 0.132 d) 0.232 e) 0.547

19.

a) (8 pts) Calculate the mass of ammonia (molar mass = 17.01) that can form when 3.82 g of magnesium nitride (molar mass = 100.0) is allowed to interact with 7.73 g of water (molar mass 18.00). Mg3N2 + 3 H2O 2 NH3 + 3 MgO

b) (2 pts) Identify the limiting reagent. 20.

______________________

(12 pts) Classify the following chemical reactions using as many correct terms as appropriate. List A: single-displacement, double-displacement, combustion, decomposition, combination List B: oxidation-reduction, acid-base, precipitate formation a) Mg(s) + 2 AgNO3(aq) 2 Ag(s) + Mg(NO3)2(aq) List A:_____________________________ List B:_____________________________ b) 2 HNO3(aq) + Ba(OH)2(aq) Ba(NO3)2(aq) + 2 H2O(l) List A:_______________________ List B:_______________________ c) CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l) List A:_____________________________ List B:_____________________________

21.

(8 pts) Complete and balance each chemical equation. Use the Solubility Guidelines to indicate the physical state of each product produced ("s" solid, "aq" aqueous, "g" gas, "l" liquid). Also, write the net ionic equation. a) _____Na2S(aq) + _____Zn(NO3)2(aq)

b) _____K2CO3(aq) + _____FeCl3(aq)

6 ABBREVIATED RULES OF SOLUBILITY OF SALTS AND BASES IN WATER All nitrates, chlorates, and acetates are soluble except the acetates of Ag and Hg(l), which are moderately soluble. Practically all sodium, potassium, and ammonium salts are soluble. All chlorides, bromides, and iodides are soluble except those of Ag, Hg(I) and Pb(II). All fluorides are soluble except those of Mg, Ca, Sr, Ba, and Pb(II). All sulfates are soluble except those of Sr, Ba, and Pb(II), which are insoluble, and those of Ca and Ag, which are moderately soluble. All carbonates, sulfites, phosphates, oxalates, and chromates are insoluble except those of Na+, K+, NH4+. All sulfides are insoluble except those of the alkali and alkaline earth metals and NH4+. All hydroxides are insoluble except those of the alkali metals. The hydroxides of Ca, Sr, and Ba are moderately soluble.

Periodic Table of the Elements

1A 1 1 H 1.01 3 Li 6.94 11 Na 23.0 19 K 39.1 37 Rb 85.5 55 Cs 133 87 Fr (223) 2A 2 4 Be 9.01 12 Mg 24.3 20 Ca 40.1 38 Sr 87.6 56 Ba 137 88 Ra 226 3B 3 21 Sc 45.0 4B 4 22 Ti 47.9 5B 5 23 V 50.9 41 Nb 92.9 73 Ta 181 6B 6 24 Cr 52.0 42 Mo 95.9 74 W 184 7B 7 25 Mn 54.9 43 Tc (98) 75 Re 186 8 26 Fe 55.8 44 Ru 101 76 Os 190 3A 13 5 B 10.8 10 28 Ni 58.7 46 Pd 106 78 Pt 195 1B 11 29 Cu 63.5 47 Ag 108 79 Au 197 2B 12 30 Zn 65.4 48 Cd 112 80 Hg 201 13 Al 27.0 31 Ga 69.7 49 In 115 81 Tl 204 4A 14 6 C 12.0 5A 15 7 N 14.0 6A 16 8 O 16.0 16 S 32.1 34 Se 79.0 52 Te 128 7A 17 8A 18 2 He 4.00

1. 2. 3. 4. 5. 6. 7. 8.

8B

9 27 Co 58.9 45 Rh 103 77 Ir 192

15 14 P Si 28.1 31.0 33 32 As Ge 72.6 74.9 50 Sn 119 82 Pb 207 51 Sb 122 83 Bi 209

9 10 F Ne 19.0 20.2 18 17 Ar Cl 35.5 39.9 36 35 Kr Br 79.9 83.8 54 53 Xe I 127 131

39 40 Y Zr 88.9 91.2 57 La 139 72 Hf 178

85 86 84 At Rn Po (209) (210) (222)

89 104 105 106 107 108 109 110 Ac Rf Db Sg Bh Hs Mt Ds 227 (261) (262) (263) (262) (265) (266) (281)

Lanthanides

58 Ce 140 90 Th 232

59 Pr 141 91 Pa 231

Actinides

60 61 62 63 64 65 66 67 68 69 70 71 Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 144 (145) 150 152 157 159 162 165 167 169 173 175 92 93 94 95 96 97 98 99 100 101 102 103 U Np Pu Am Cm Bk Cf Es Fm Md No Lr 238 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (260)

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