Chem 1201 Sample Exam 4

Chem 1201 Sample Exam 4 - CHEMISTRY 1201 Modified Sample...

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Unformatted text preview: CHEMISTRY 1201 Modified Sample Examination IV (Chapters 9-10) (In previous years, Exam 4 included questions from Ch. 11, but NOT this year) Time allowed: 75 minutes CALCULATORS ARE PERMITTED IN THIS EXAMINATION 1. One significant difference between gases and liquids is that A. a gas can only be made of nonpolar molecules B. a gas assumes the entire volume of a container C. gases are always mixtures D. gases are always colorless and odorless at room temperature E. gases cannot be compressed . 2. In ideal gas calculations, expressing pressure in Pascals (Pa) necessitates the use of the gas constant, R, equal to . − − A. 0.082057 atm L mol 1 K 1 − − B. 8.314 J mol 1 K 1 − − C. 4.184 J g 1 K 1 − − D. 1.987 cal mol 1 K 1 E. none of the above A line for CH4 is expected to be found . 3. A. between the lines for H2 and He B. between the lines for He and H2O C. between the lines for N2 and O2 D. to the right of (behind) the line for H2 E. to the left of (in front of) the line for O2 1 4. A sample of gas at 1.0 atm is expanded at constant temperature from 10. L to 15 L. What is the final pressure? A. 1.5 atm B. 7.5 atm C. 0.67 atm D. 3.3 atm E. 15 atm 5. What is the approximate rms speed of methane, CH4, at STP conditions? A. 65 ms 1 − B. 380 ms 1 − C. 650 ms 1 − D. 1.4 x 105 ms 1 − E. 4.3 x 105 ms 1 − 6. A sample of methane gas occupies 57.9 L at 300.0 K at 1.00 atm. What is volume of this sample at 423 K and 2.00 atm? A. 2.45 L B. 4.88 L C. 20.5 L D. 40.8 L E. 41.1 L 7. What is the mole fraction of CO2 gas in a sample of air, which consists of 0.756 mole of N2, 0.189 mole of O2, and 0.0132 mole of CO2? A. 0.789 B. 0.0138 C. 0.140 D. 1.003 E. 1.27 8. Methane (CH4) effuses about 2.4 times faster than a certain unknown gas. Which of the following would you suspect of being the unknown gas? A. O2 B. C2H6 C. CH3Br D. CH3I E. F2 2 9. The air bags in cars are inflated when a collision triggers the explosive, highly exothermic decomposition of sodium azide, NaN3: 2 NaN3(s) 2 Na(s) + 3 N2(g) A typical driver-side air bag contains about 50 g of NaN3. Determine the volume of N2 gas that would be generated by the decomposition of 50.0 g of sodium azide at 85°C and 1 atm. A. 0.769 L B. 1.15 L C. 8.02 L D. 15.1 L E. 33.9 L 10. SiF62 exists, but CF62 does not. Why? Consider the concept of hybrid orbitals in your answer. A. Silicon is less electronegative, so its hybrid orbitals are lower in energy. B. Silicon is more electronegative, so its hybrid orbitals are higher in energy. C. Silicon can hybridize using nearby 3d orbitals. Such orbitals are not available to carbon since it is located in the second period of the periodic table. D. Carbon is never found in 2- ions. E. Silicon is unusual, and hybridization is irrelevant. − − 11. Which option gives the correct approximate bond angles in the structure below? Angle 1 A. B. C. D. E. 180° 120° 109° 120° 120° Angle 2 109° 120° 90° 90° 90° Angle 3 120° 109° 109° 120° 109° 3 12. How many sp hybridized carbon atoms are there in the following structure? A. 1 B. 2 C. 3 D. 4 E. 6 13. Xenon tetrafluoride, XeF4, has A. tetrahedral, sp3 B. see-saw, sp3d C. T-shape, sp3d D. square planar, sp3d2 E. square pyramidal, sp3d2 molecular shape and Xe is hybridized. 14. A molecule with the following molecular shape is expected to be . A. unstable, because the sp3d2 hybridization of the central atom demands the presence of the 6th terminal atom B. gaseous at room temperature, because the terminal atoms are likely fluorine atoms C. polar, due to the presence of one lone pair of electrons on the central atom D. nonpolar, because of the expanded octet of electrons on the central atom E. nonpolar, because the sum of individual bond dipoles is zero 15. Which of the statements below best describes formaldehyde shown below: A. there are 3 σ bonds and 1 π bond in formaldehyde and the molecule is trigonal planar B. there are 3 σ bonds and 1 π bond in formaldehyde and the molecule is trigonal pyramidal C. there are 2 σ bonds and 1 π bond in formaldehyde and carbon has sp2 hybridization D. there are 2 σ bonds and 2 π bond in formaldehyde and carbon only uses unhybrized orbitals to bond with H and O atoms E. all σ and π bonds utilize hybridized orbitals on the central C atom 4 16. Identify the polar molecule(s) in the following group: HBr, CH4, SO2. A. HBr only B. HBr and SO2 C. HBr, CH4 and SO2 D. CH4 and SO2 E. CH4 only 17. Which of the statements below is true for benzene, C6H6: A. There are 9 carbon-carbon σ bonds in a molecule of benzene. B. There is a total of 9 localized σ bonds and 3 delocalized π bonds in a molecule of benzene. C. All 6 carbon-carbon bonds in benzene are shorter and stronger than an average single C− bond. C D. Each carbon atom utilizes 2 sp2 hybrids in the resonance hybrid of benzene shown to the right. E. There is a total of 18 valence electrons in benzene. 18. SCl2 has a nonzero net dipole moment, but BeCl2 has a net dipole moment of zero. How can you explain the difference? A. S is more massive than Be. B. Be forms a double bond with one of the Cl atoms. C. S can expand its octet. D. S has two lone pairs of electrons. E. S is more electronegative than Be. 19. Which of the following shapes is not possible for a molecule in which the central atom has sp3d hybridization? A. T-shaped B. tetrahedral C. trigonal bipyramidal D. see-saw E. linear 5 20. Which of the following two isomers of 2,3-dichloro-2-butene is polar and why? Note: both parts of the answer have to be correct to receive credit for this question. A. (i); the molecule is two-dimensional (flat). B. (i); the two C-Cl bond dipole moments contribute to a non-zero net dipole moment. C. (ii); all C-C-C and C-C-Cl bond angles are 120°, which always ensures molecular polarity. D. (ii); the two C-Cl bond dipole moments cancel out. E. nonsense; neither isomer is polar. 21. Assuming the volume of each breath (inhale or exhale) is 0.5 L, calculate the number of molecules exhaled in each breath at body temperature (37°C) at 1 atm. A. 1 × B. 1 × C. 1 × D. 6 × E. 6 × 1021 1022 1023 1022 1023 22. Sodium reacts with water to form sodium hydroxide and hydrogen gas according to the equation: 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) If 90.0 grams of sodium are dropped into 80.0 g of water and the H2(g) is collected in a 15.0 L container at 298 K, what is the pressure of H2(g) in this container? A. 1.60 atm B. 3.19 atm C. 3.61 atm D. 6.38 atm E. 7.24 atm 6 23. What is the molar mass of a gas which at 25°C and a pressure of 99,992 Pa has a density of 2.35 kg/m3? A. 7.76 g/mol B. 44.1 g/mol C. 49.1 g/mol D. 58.2 g/mol E. 92.5 g/mol 24. The drawing below represents a mixture of three different gases. If the total pressure of the mixture is 0.90 atm, what is the partial pressure of the gas symbolized by . A. 0.54 atm B. 0.45 atm C. 0.27 atm D. 0.18 atm E. 0.090 atm 25. Approximately, at what temperature does a collection of He gas atoms become supersonic? Note: speed of sound is 340.29 m/s. A. 0.54 K B. 4.0 K C. 9.4 K D. 18.6 K E. 185.5 K 7 Answer Key: 1B, 2B, 3B, 4C, 5C, 6D, 7B, 8C, 9E, 10C, 11B, 12B, 13D, 14C, 15A, 16B, 17C, 18D, 19B, 20B, 21B, 22B, 23D, 24B, 25D 8 ...
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This note was uploaded on 03/21/2011 for the course CHEM 1201 taught by Professor Cook during the Fall '08 term at LSU.

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