CHE 105 - Mid-Term Examination III - 11 April 1996
University of Kentucky Department of Chemistry
1. What is the electron pair arrangement about the central atom of XeF4?
A. trigonal planar B. tetrahedral C. octahedral D. trigonal bipyramidal
2. Which of the following have the tetrahedral molecular geometry?
NH3, NH4+, H2O, ClF4-, CF4
A. NH3, NH4+, H2O, CF4 B. NH4+, CF4 C. NH4+, ClF4-, CF4 D. all of them
3. Which of the following molecules are polar?
XeO2F2, XeOF4, XeF4, ClF3
A. XeOF4 and ClF3 B. ClF3 and XeF4 C. XeO2F2, XeOF4, and ClF3 D. All of the above.
4. The molecular geometry of XeF4 and hybridization of the central Xe atom are:
A. square planar; sp3d2 B. square planar; sp3 C. octahedral; sp3 D. octahedral; sp3d2
5. Which statement is correct concerning the valence bond theory of H2O?
A. The two sp hybrid orbitals of oxygen overlap with the 1s orbital of each hydrogen forming sigma bonds. B. Two of the sp2 hybrid orbitals of oxygen overlap with the 1s orbital of each hydrogen forming sigma bonds. The remaining sp2 hybrid orbital contains a lone pair of electrons. C. Two of the sp3 hybrid orbitals of oxygen overlaps with the 1s orbital of each hydrogen forming sigma bonds. The remaining two sp3 hybrid orbitals contain a lone pair each. D. The half-filled 2p orbitals of oxygen overlaps with the 1s orbitals of hydrogen to form sigma bonds. The lone pair are contained in the 2s and 2p orbitals of oxygen.
6. According to valence bond theory, which of the following pairs of atomic orbitals can combine to form hybrid orbitals?
A. 2s and 3s B. 2px and 2py C. 2p and 2s D. 4d and 3p
7. The number of sigma and pi bonds in ethene (C2H4) are:
A. 4 sigma, 1 pi B. 4 sigma, 0 pi C. 1 sigma, 1 pi D. 5 sigma, 1 pi
8. Which statement(s) is(are) false concerning CO2?
1. The molecular geometry is linear. 2. The electron pair arrangement is linear. 3. The C-O bond is polar. 4. The molecule is polar
A. 4 B. 2, 4 C. 1, 3 D. 1, 2
9. Which statement is false?
A. Valence Bond Theory describes bonds as being formed by atoms sharing valence electrons in overlapping valence orbitals. B. Hybrid orbitals are the mathematical mixing of two or more orbitals on the same atom. C. When three orbitals are mixed to form hybrid orbitals, three hybrid orbitals are always formed. D. The overlap of p orbitals on adjacent atoms always results in a pi bond.
10. A molecular orbital is a wave function of an electron in a(n) ___________. Molecular orbitals are formed by combining valence orbitals of ____________.
A. atom; an atom B. molecule; an atom C. atom; more than one atom D. molecule; more than one atom
11. Which of the following is the correct valence shell molecular orbital configuration of OF+? (Assume the same energy level diagram as for homonuclear diatomic molecules.)
12. According to molecular orbital theory, the bond order and number of unpaired electrons in N2- are:
A. 2.5, 1 B. 3, 0 C. 3, 1 D. 2.5, 0
13. Which of the following molecules are diamagnetic?
O2, NO, CH4, H2O
A. O2 and NO B. CH4 and H2O C. CH4, O2, and H2O D. none of the above
14. If the atmospheric pressure is 724 torr, which statement is true concerning the following diagrams (where h1 = h2) ?
15. Which of the following is(are) true?
1. At constant temperature a sample of gas will increase in pressure as volume increases. 2. At constant pressure a sample of gas will increase in pressure as the temperature increases. 3. At constant pressure and temperature as the number of moles increases of a gas, the volume increases.
A. 1, 2, and 3 are true B. 2 and 3 are true C. 2 is true D. 3 is true
16. A gas at 25oC and 1.00 atm is heated to 100oC at constant volume. What is the final pressure?
A. 1.25 atm B. 0.799 atm C. 0.250 atm D. 4.00 atm
17. Which of the following is correct for 2 moles of an ideal gas?
18. What is the molar mass of a gas if 10.0 g of the gas occupy 8.21 L at 380.0 torr and 27oC?
A. 1.88 g/mol B. 60.0 g/mol C. 16.7 g/mol D. 127 g/mol
19. For the reaction
A(g) + 3 B(g) ---> 3 C(g)
If 1.5 L of A reacts with 1.5 L of B, how many liters of C are formed?
A. 1.5 L C> B. 3.0 L C C. 4.5 L C D. Cannot be determined without more information.
20. What volume of H2 gas will be produced at 50oC and 1 atm from the reaction of 2.0 g of Na metal with excess water?
2 Na(s) + 2 H2O(l) ---> H2(g) + 2 NaOH(aq)
A. 0.83 L B. 2.3 L C. 0.18 L D. 1.2 L
21. A 50.0 mL sample of N2 gas is collected over water at 26oC at a pressure of 756 torr. Given that the vapor pressure of water at 26oC is 25 torr, how many grams of N2 gas were collected?
A. 5.7 mg B. 63 g C. 67 g D. 5.5 mg
22. Which of the following statements are true concerning the behavior of gas at the molecular level?
1. Pressure of a gas arises from collisions of gas molecules with the walls of the container. 2. At constant temperature, pressure of the gas increases with decreased volume because there is less area over which the collision can occur. 3. Collisions of ideal gas particles with each other and the container walls are perfectly elastic. 4. As the temperature increases, the average kinetic energy of the molecules increases.
A. 3, 4 B. 1, 4 C. 1, 2, 4 D. 1, 2, 3, 4
23. Which of the following are true statements?
1. PV/RT for 1 mole of a real gas is equal to 1 at any temperature and pressure. 2. The average kinetic energy of 1 mole of O2(s) at 200oC is equal to the average kinetic energy of 1 mole of SF6(s) at 200oC. 3. The average speed of 1 mole of O2(s) molecules at 200oC is greater than the average speed of 1 mole of SF6(s) molecules at 200oC. 4. The kinetic molecular theory of gases assumes that gases are made up of large, sticky particles.
A. 1 and 4 B. 1 and 2 C. 2 and 3 D. 3 and 4
24. Under the same conditions of temperature and pressure, a gas is found to diffuse at 0.707 times the rate of diffusion of CH4. The gas could be:
A. O2 B. N2 C. H2 D. He
25. Real gases approach ideal behavior at:
A. low pressures and low temperatures. B. low pressures and high temperatures. C. high pressures and low temperatures. D. high pressures and high temperatures.