Please sit in Row_____ Seat_____ Name_____PRACTICE_______________________

Chem 105X

Dec. 10, 2010

Keller

ABCDEG

Hour Exam 4 Chap 9, 10, 11 Kotz

Please:

 Keep this booklet closed until instructed to open it.  Turn off and remove from your person all electronic items including PDAs, cell phones, earbuds, pagers, computers, programmable and graphing calculators, and other similar devices. Place them in your purse or pack on the floor or at the back of the room.  Place all papers, periodic tables, books, coats, packs, on the floor or at the front or back of the room.  All you need are #2 pencils & a non-programmable calculator.

Exam Directions  NOW PRINT YOUR NAME and fill in your STUDENT ID (a number like “309300001” - but not this number) and the letter of the exam on the bubble sheet.  This is a closed book, 60-minute exam. Use nothing but the materials supplied to answer the questions.  There are a total of 8 pages in this exam, including the cover and back sheets.  The attached back sheet contains reference information including constants and periodic table.  For questions 21, show your work, use the correct number of significant figures, and include proper units in answer and in the work. Write legibly: if your answer cannot be read by the grader, no credit can be given.  After you begin, PRINT YOUR NAME at the top of BOTH PAGE 6 and PAGE 7.

Part I. Multiple Choice 4 POINTS EACH Identify the letter of the choice that best completes the statement or answers the question. PUT YOUR ANSWER ON THE BUBBLE SHEET PROVIDED. Marks in this section of the exam booklet will not be graded.

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1. Which of the following statements is/are CORRECT? 1. The overlap between an s orbital and a p orbital is called a pi-bond. 2. The overlap of two s orbitals in H2 is called a sigma bond. 3. HF is formed from the overlap of a hydrogen 1s orbital with a fluorine 2s orbital. a. b. c. d. e.

1 only 2 only 3 only 2 and 3 1, 2, and 3

____ 2. How many sigma () bonds and pi () bonds are in ethene, C2H4? a. four , one  b. four , two  c. five , one  d. five , two  e. six , zero 

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3. What is the hybridization of the xenon atom in XeF2? a. sp b. sp2 c. sp3 d. sp3d e. sp3d2

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4. Which of the underlined atoms (C1, C2, N, and O) are sp2 hybridized?

a. b. c. d. e.

C1 and C2 C1, N, and O N and O O and C2 O only

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5. All of the following statements concerning molecular orbital (MO) theory are correct EXCEPT a. the Pauli exclusion principle is obeyed. b. Hund's rule is obeyed. c. electrons are assigned to orbitals of successively higher energy. d. a bonding molecular orbital is lower in energy than its parent atomic orbitals. e. the combination of two atomic orbitals creates only one molecular orbital. Diagram 9-1 The molecular orbital diagram below may be used for the following problem(s). For oxygen and fluorine, the 2p orbital should be lower in energy than the 2p. However, the diagram will still yield correct bond order and magnetic behavior for these molecules. Energy

________ ________

________ *2p ________

________

*2p

2p

________ 2p ________

*2s

________

2s

________

*1s

________

1s

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6. Refer to Diagram 9-1. According to molecular orbital theory, which of the following species has the highest bond order? a. F2 b. F22+ c. C22– d. Li2 e. B22+

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7. Refer to Diagram 9-1. Use molecular orbital theory to predict which ion is paramagnetic. a. F22+ b. O22– c. O22+ d. N22+ e. B22–

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____ 8. In butadiene CH2=CH-CH=CH2, a component of rubber, each atom can be viewed as sp2 hybridized. Thus, each atom has one remaining unhybridized p orbital. How many 2p molecular orbitals (including both bonding and antibonding orbitals) are formed using the unhybridized p orbitals? a. 1 b. 3 c. 4 d. 6 e. 12 ____

9. Which of the following molecules might be an alkyne? a. C3H6 b. C4H10 c. C5H10 d. C6H10 e. C6H12

____ 10. What is the name of the following compound?

a. b. c. d. e.

1,1,3-trimethylpentane 2,4-dimethyloctane 3-methyl-4-propylbutane 3,5-dimethylhexane 2,4-dimethylhexane

____ 11. At constant temperature, 12.5 L of N2 at 262 mm Hg is compressed to 4.15 L. What is the final pressure of N2? a. 5.05 mm Hg b. 87.0 mm Hg c. 262 mm Hg d. 789 mm Hg e. 873 mm Hg

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____ 12. The lid is tightly sealed on a rigid flask containing 4.20 L O2 at 27 C and 0.969 atm. If the flask is heated to 81 C, what is the pressure in the flask? a. 0.821 atm b. 1.14 atm c. 1.18 atm d. 2.91 atm e. 3.45 atm

____ 13. A balloon is filled with N2 gas to a volume of 1.92 L at 37 C. The balloon is placed in liquid nitrogen until its temperature reaches –142 C. Assuming the pressure remains constant, what is the volume of the cooled balloon? a. –0.500 L b. 0.500 L c. 0.811 L d. 1.43 L e. 4.54 L

____ 14. Which of the following relationships is/are CORRECT for gases? 1. The moles of a gas is inversely proportional to its volume (at constant pressure). 2. The volume of a gas is inversely proportional to its temperature in kelvin (at constant pressure). 3. The pressure of a gas is directly proportional to its temperature in kelvin (at constant volume). a. b. c. d. e.

1 only 2 only 3 only 1 and 2 2 and 3

____ 15. The pressure of N2 in a 20.0 L flask is 0.603 atm at 62 C. What mass of N2 is in the flask? a. 0.439 g b. 6.15 g c. 12.3 g d. 63.9 g e. 66.4 g

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____ 16. Sodium azide decomposes rapidly to produce nitrogen gas. 2 NaN3(s)  2 Na(s) + 3 N2(g) What mass of sodium azide will inflate a 56.6 L airbag for a car to a pressure of 811 mm Hg at 25 C? a. 17.6 g b. 39.5 g c. 107 g d. 161 g e. 241 g

____ 17. The empirical formula of a certain hydrocarbon is CH2. When 0.131 mole of the hydrocarbon is completely combusted with excess oxygen, 16.1 L CO2 gas is produced at 27 C and 1.00 atm. What is the molecular formula of the hydrocarbon? a. C2H2 b. C2H4 c. C3H6 d. C5H10 e. C6H12

____ 18. Which of the following statements are postulates of the kinetic-molecular theory of gases? 1. Gas particles are in constant, random motion. 2. The distance between gas particles is large in comparison to their size. 3. The kinetic energy of gas particles is inversely proportional to the kelvin temperature. a. b. c. d. e.

1 only 2 only 3 only 1 and 2 1, 2, and 3

____ 19. If a gas effuses 2.165 times faster than Xe, what is its molar mass? a. 12.94 g/mol b. 28.01 g/mol c. 32.00 g/mol d. 60.65 g/mol e. 284.3 g/mol

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____ 20. Which of the following statements concerning real gases is/are CORRECT? 1. Real gases are always liquids or solids at temperatures below 273.15 K. 2. The pressure of a real gas is higher than predicted by the ideal gas law. 3. The molecules in a real gas are attracted to each other. a. b. c. d. e.

1 only 2 only 3 only 2 and 3 1, 2 and 3

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ABCDEG Name_____________________________________

Part II. For full credit, you must show all conversion factors and the final answer with complete units, use the correct number of significant figures, and round off correctly. WRITE CLEARLY: if the grader cannot read your writing, no credit will be assigned.

Question 21 (12 pts) What volume of wet CO2 gas (1.000 atm, 30.00°C) will be collected in a gas buret from the reaction of 4.066 g of sodium carbonate with excess sulfuric acid? (Hint: first write the balanced chemical equation.) The vapor pressure of water at 30.00°C is 31.50 mmHg.

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ABCDEG Name_____________________________________ Question 22 (8 pts)

Write clear Lewis formulas for THREE structural isomers of C6H12 that contain THREE METHYL groups (-CH3). For example, the molecule shown below fits this description. Show all hydrogens. Geometric isomers do not count.

(CH3)2C=CHCH2CH3

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Avogadro’s number = 6.0221 x 1023

R = gas constant = 0.08206 L-atm/mol-K = 8.314 J/mol-K

1 amu = 1.661 x 10-24 g

1 mile = 5280.0 ft

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