Name October 1, 2012 Recitation TA on 8 pages Exam Practice...The heat exchanged during the solution process when solid sodium hydroxide dissolves in water is +44.4 kJ/mol. When a

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Prof. Thomas Greenbowe Prof. Gordon Miller Dr. Cristina Bonaccorsi This exam consists of 2 parts on 8 pages

CHEM 177 Hour Exam II

October 1, 2012

Name______________________ Recitation TA_______________ Recitation Section____________

Grading

Parts

Page 3

Page 4

Page 5

Page 6

Page 7

SUBTOTAL

Grand Total

Points

15 pts

21 pts

26 pts

26 pts

12 pts

64 pts

100 pts

Score

on scantron sheet

________

________

________

________

________

TA Name Sections Time Berry 14, 38 10, 2 Bobbitt 36, 48 2, 3 Boschen 3, 9 8, 9 Burgin 53, 58 4, 5 Carraher 6, 12 9, 10 Castle 40, 46 2, 3 Chaudhary 47 3 Cole 19 11 De Silva 21, 31 11, 1 Flood 54 5 Friedrichsen 7, 30 9, 1 Ganesh 5, 11 8, 9 Geraskin 20, 26 11, 12 Geraskina 17, 23 10, 11 Hochstein 35, 42 1, 2 Joshi 16, 29 10, 12 Keller 1 8 Khan 22, 49 11, 4 Kumar 28, 34 12, 1 Kwolek 4, 10 8, 9 Lei 44, 52 3, 4 Lesoine 15, 57 10, 5 Nelson 33, 41 1, 2 Nguyen 24 12 Peeraphatdit 32, 39, 45 1, 2, 3 Thooft 43, 51 3, 4 Vangaveti 18, 27 11, 12 Wang 50, 55 4, 5 Wanninayake 2, 8 8, 9 Weerasekara 13, 25 10, 12 Xu 37, 56 2, 5

NOTE: To receive full credit for problems on pages 5-7: #13-16, you must clearly show all work and your method of determining the answer must be clear. The final answer must be reported to the correct number of significant figures and have the correct units. Questions are written on both sides of each page. The last page contains useful information and a periodic table; the last page may be removed and used for scratch paper and as a reference. Do not put answers on the tear away page.

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Please read the following instructions carefully before proceeding! Part I of your exam will be computer graded. In order for the computer to identify who you are, it is important that you complete the information section properly.

You must use a #2 pencil and completely fill in the appropriate circles on the BLUE computer scan sheet. 1. 2.

3.

To help you code the correct circles, first write your last name, first name, and middle initial in the boxes (skip a space between each). Then darken the circles that match the letters in the box above it. See the sample to the right. Write the middle nine digits of your ISU identification number in the boxes A-I. Do not skip any spaces. Below each number, darken the circle that matches this number. For example, 123456789. See the sample at bottom right.

Write your recitation section number in the special code area, boxes K-L, as two digits. Do not skip any spaces. For example, if you are in section 8, write 08. Again, darken the circle that matches the number above it. See the sample at bottom far right.

In Part I, select the one best answer for each question. Place your answer on the computer answer sheet by darkening the proper circle for that question. Your computer scan sheet will be your official answer sheet for Part I. All material (exam, answer sheet, scratch paper) must be returned to your TA in order for us to grade your exam.

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Part I: Multiple Choice (12 questions at 3 pts each = 36 points). The answer you fill in on your bubble sheet is the one that will count. You should circle the answer on this sheet for your own reference. There is only one best answer for each question. 1. The reaction Na3PO4(aq) + 3 HNO3(aq) H3PO4(aq) + 3 NaNO3(aq) is best classified as a(n)

a) acid-base reaction b) oxidation-reduction reaction c) precipitation reaction d) combustion reaction

2. Assume that an aqueous solution of a cation, represented by shaded spheres, is allowed to mix with a solution of an anion, represented by unshaded spheres. Three possible outcomes are represented by boxes (a) – (c).

Which outcome corresponds to the combination of calcium and carbonate ions:

Ca2+(aq) + CO32–(aq) ?

a) box (a) b) box (b) c) box (c) d) none of these

3. Acetic acid (CH3CO2H), formic acid (HCO2H), hydrofluoric acid (HF), ammonia (NH3), and

methylamine (CH3NH2) are commonly classified as

a) acids b) nonelectrolytes c) strong electrolytes d) weak electrolytes

4. How many milliliters of a 3.45 M lead nitrate solution are needed to make 450.0 ml of 0.990 M solution of lead nitrate?

a) 129 mL b) 109 mL c) 101 mL d) 56 mL

5. What is the molarity of an aqueous solution containing 75.3 g of glucose in 35.5 mL of solution?

(glucose, C6H12O6, F.W. = 180.12 g/mol)

a) 1.85 M b) 2.12 M c) 0.197 M d) 11.8 M

(a) (b) (c)

cation anion

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6. Solid aluminum and gaseous oxygen react in a combination reaction to produce aluminum oxide:

4 Al (s) + 3 O2 (g) → 2 Al2O3 (s)

In a particular experiment, the reaction of 2.5 g of Al with an excess of O2 produced 3.5 g of Al2O3. What is the % yield of the reaction? (FW of Al2O3 is 102.0 g/mol.) a) 74% b) 37% c) 47% d) 66%

7. How many grams of sodium chloride are there in 550.0 mL of a 1.90 M aqueous solution of sodium

chloride?

a) 1.05 g b) 30.5 g c) 61.1 g d) 122 g 8. The value of ∆E for a system that performs 13.0 kJ of work on its surroundings and loses 9.0 kJ of heat

is ______________kJ.

a) 22 b) 13 c) 4 d) +4 e) +22

9. A chemical reaction that absorbs heat from the surroundings is said to be _____________ and has a

____________________ enthalpy change, ∆H, at constant pressure.

a) endothermic, positive c) exothermic, positive b) endothermic, negative d) exothermic, negative

10. The heat exchanged during the solution process when solid sodium hydroxide dissolves in water is

+44.4 kJ/mol. When a 10.1 g sample of NaOH dissolves in 250.0 g of water in a calorimeter, the temperature increases from 23.0°C to ________________°C. Assume that the solution has the same specific heat as liquid water, 4.18 J/g K. (FW of NaOH is 40.0 g/mol.; assume heat change of the calorimeter to be negligible.)

a) 24.0 b) 33.3 c) 33.7 d) 35.2 e) 40.2

11. Which of the following conditions would always result in a decrease in the internal energy of a system?

a) The system loses heat and does work on the surroundings. b) The system gains heat and does work on the surroundings. c) The system loses heat and has work on it by the surroundings. d) The system gains heat and has work done on it by on the surroundings.

12. A 10.0 g sample of silver is heated to 100.0°C and then added to 20.0 g of water at 23.0°C in an

insulated calorimeter. At thermal equilibrium the temperature of the system was measured at 25.0°C. Assume the specific heat for water is 4.18 J/g°C. What is the specific heat of silver?

a) 0.11 J/g°C b) 0.22 J/g°C c) 17 J/g°C d) 34 J/g°C

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Total Pts ________

Part II: Problems (64 points total). Show all work to receive credit. Place your answers in the answer spaces. 13. (14 pts) Complete and balance each of the following reactions using neutral species. Write NR for

no observable reaction. Identify any spectator ions in the solution and write net ionic reactions. Use the solubility rules to indicate, when appropriate, “(aq)” “(s)”, “(g)”, or “(l)”. (a) ____ (NH4)2S(aq) + ____ Ba(NO3)2(aq)

Spectator Ions: __________________________________________________ Net Ionic Equation: __________________________________________________ What is the name of (NH4)2S(aq)? ________________________________

(b) ____ Pb(NO3)2(aq) + ____ Na2SO4(aq) Spectator Ions: ____________________________________________ Net Ionic Equation: ____________________________________________ What is the name of Na2SO4(aq)? __________________________ 14. (12 pts) In the following reactions, identify the elements or species undergoing oxidation and

reduction. Identify the oxidation states of these elements in the reactant(s) and in the product(s).

(a) 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g)

Element / Species Oxidation State in Reactants(s) Oxidation State in Product(s)

Oxidation:

Reduction:

(b) PbS(s) + 4 H2O2(aq) PbSO4(s) + 4 H2O(l)

Element / Species Oxidation State in Reactants(s) Oxidation State in Product(s)

Oxidation:

Reduction:

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Total Pts ________

15. (26 points; in five parts on this page) When 75.0 mL of 0.100 M Na2CO3(aq) and 25.0 mL of 0.200 M AgNO3(aq) solutions are mixed together in a calorimeter, a white precipitate forms (see balanced equation below). The initial temperature of both solutions is 25.0°C. The final volume is 105.0 mL.

(a) (2 pts) Fill in the phases, i.e., (s), (l), (g), (aq), for the products in the spaces provided below:

Na2CO3(aq) + 2 AgNO3(aq) Ag2CO3 _____ + 2 NaNO3 _____

(b) (4 pts) What is the net ionic equation for the reaction that occurs?

Ans. _____________

(c) (8 pts) What is the limiting reagent in this reaction?

Ans. _____________

(d) (8 pts) What is the theoretical yield in grams for the precipitate formed?

Ans. _____________

(e) (4 pts) Given that the enthalpy change for the reaction is exothermic, will the temperature of the solution increase or decrease as the reaction occurs? Briefly explain.

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Total Pts ________

16. (12 points; in three parts on this page) An unknown monoprotic acid, HA(aq), is titrated with a standard solution of sodium hydroxide.

(a) (6 pts) Calculate the concentration (in molarity) of the acid solution if 18.40 mL of the 0.1502 M NaOH solution are needed to neutralize 25.00 mL of the acid solution.

Ans. _____________

(b) (2 pts) The acid solution titrated above (25.00 mL) contains 0.101 g of HA. What is the identity of

the acid? Circle your choice below.

a) HCl (FW = 36.6 g/mol) b) HBr (FW = 80.9 g/mol) c) HI (FW = 128 g/mol) (c) (4 pts) The acid solution titrated above was obtained from a stock solution of the acid. Calculate the

concentration (in molarity) of the stock acid solution knowing that a 10.00-mL aliquot of the stock acid solution was used to make the 25.00-mL solution used in the titration. (If you do not have an answer to part (a), use 0.1500 M as the concentration of the unknown acid in 25.00 mL.)

Ans. _____________

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INFORMATION

1 mole = 6.022 1023 molecules Esystem = Esurroundings

1 L = 1000 mL = 1000 cm3 E = q + w q = mCsT ΔH = qp 1 kJ = 1000 J qreaction + qsolution = 0 1 K = 1C

Rule for Oxidation States of Elements in Compounds

(1) 0 in elements (5) Oxygen: 2, except for peroxides (O22: 1)

(2) Alkali metals: +1 (6) Halogens (Cl, Br, I): 1, except when combined with F or O (3) Alkaline-earth metals: +2 (7) Hydrogen: +1 with nonmetals; 1 with metals (4) Fluorine: 1 (8) Sum of oxidation states in molecule/ion = total charge

Solubility Rules:

Soluble Compounds contain … except …

Alkali metals (Li+, Na+, K+, Rb+, Cs+) and NH4+ -

Nitrate (NO3), acetate (C2H3O2

), and bicarbonate (HCO3

) ions -

Halides (Cl, Br, I) ions Halides of Ag+, Hg22+, Pb2+

Sulfate (SO42) ions Sulfates of Ag+, Ca2+, Sr2+, Ba2+, Pb2+

Insoluble compounds contain … except … Carbonate (CO3

2), phosphate (PO43), sulfide (S2) ions those with alkali metal ions or NH4

+

Hydroxide (OH) ions those with alkali metal ions or NH4+ or Ba2+

Periodic Table of the Elements

103 Lr

(260)

102 No

(259)

101 Md

(258)

100 Fm

(257)

99 Es

(252)

98 Cf

(251)

97 Bk

(247)

96 Cm

(247)

95 Am

(243)

94 Pu

(244)

93 Np

(237)

92 U

238

91 Pa

231

90 Th 232

71 Lu 175

70 Yb

173

69 Tm 169

68 Er

167

67 Ho

165

66 Dy

162

65 Tb 159

64 Gd 157

63 Eu 152

62 Sm 150

61 Pm

(145)

60 Nd

144

59 Pr

141

58 Ce 140

8A 18

7A 17

6A 16

5A 15

4A 14

3A 13

Lanthanides

Actinides

109 Une

(266)

108 Uno

(265)

107 Uns

(262)

106 Unh

(263)

105 Ha

(262)

104 Rf

(261)

89 Ac

227

88 Ra

226

87 Fr

(223)

83 Bi

209

82 Pb

207

81 Tl

204

80 Hg 201

79 Au 197

78 Pt

195

77 Ir

192

76 Os

190

75 Re

186

74 W

184

73 Ta 181

72 Hf

178

57 La

139

56 Ba

137

55 Cs

133

51 Sb

122

50 Sn

119

49 In

115

48 Cd 112

47 Ag 108

46 Pd

106

45 Rh

103

44 Ru

101

43 Tc

(98)

42 Mo 95.9

41 Nb

92.9

40 Zr

91.2

39 Y

88.9

38 Sr

87.6

37 Rb

85.586 Rn

(222)

85 At

(210)

84 Po

(209)

52 Te 128

53 I

127

54 Xe

131

36 Kr

83.8

35 Br

79.9

34 Se

79.0

33 As

74.9

32 Ge

72.6

31 Ga

69.7

30 Zn

65.4

29 Cu

63.5

28 Ni

58.7

27 Co

58.9

26 Fe

55.8

25 Mn 54.9

24 Cr

52.0

23 V

50.9

22 Ti

47.9

21 Sc

45.0

20 Ca

40.1

19 K

39.1

18 Ar

39.9

17 Cl

35.4

16 S

32.1

15 P

31.0

14 Si

28.1

13 Al

27.0

2 He

4.00

10 Ne

20.2

9 F

19.0

8 O

16.0

7 N

14.0

6 C

12.0

5 B

10.88B

2B 12

1B 111098

7B 7

6B 6

5B 5

4B 4

3B 3

12 Mg

24.3

11 Na

23.0

4 Be

9.01

3 Li

6.94

2A 2

1A 1

1 H

1.01