Chemistry 106: General Chemistry Syracuse University Project Advance Exam #3, Fall 2005 Name Date The last pages of each examination are reference tables. R = 0.08206 L*atm/mole*K 1) The ground-state electron configuration of S is [Ne]3s23p4, which implies there are two unpaired electrons and S can form two bonds. However, the Lewis structure of SF6 shows six S-F single bonds. This can occur because a) Electrons may be promoted into the 3d orbitals of S with a relatively small energy cost b) The 3s electrons may be promoted into the 4s subshell with a relatively small energy cost. c) All of the six electrons in the M shell (n = 3) can be unpaired with a very small energy cost. d) Electrons can be added to S from the fluorines, each of which has more electrons than S. e) Some of the electron pairs on S can be transformed into bond pairs. 2) Which of the following does not describe a covalent bond? a) electrons are attracted simultaneously to both positive nuclei forming the bond. b) involves overlapping orbitals of the atoms that compose it. c) sharing of core (inner) electrons. d) all describe covalent bonds. 3) A correct Lewis Formula for P2 is: a) P P b) P P c) P P d) P e) None of the above CHE 106 P 1 Fall 2005 Exam #3 4) Given the Lewis structure: H O Cl O Calculate the formal charges for the designated atoms: Oxygen bonded to H, Cl +1 -1 -1 0 0 a) b) c) d) e) Cl -1 +1 0 -1 +1 Oxygen bonded to Cl 0 0 +1 +1 -1 5) Which of the following statements about resonance is/are incorrect? I. When resonance exists, a single Lewis structure does not adequately represent the bonding. II. Resonance describes the vibration of nuclei within the molecule. III. Resonance describes a bonding situation that is in between the contributing structures. a) b) c) d) e) 6) I II III I and III none are incorrect Write a Lewis formula for the ion AlF63-. (Al will have more than an octet around it.) How many non-bonding electrons are there all together? (the entire atom not just the central atom) a) b) c) d) e) CHE 106 24 30 36 42 48 2 Fall 2005 Exam #3 7) What could you do to improve the Lewis structure at right? a) b) c) d) e) 8) Write a Lewis formula for the nitrate ion, NO2-. Make sure the octet rule is followed. What is the total number of bonds in your formula? (A double bond counts as two bonds, a triple bond counts as three.) a) b) c) d) e) 9) 1 2 3 4 5 The Lewis structure of acetic acid is shown at right. How many (sigma) bonds are there in the structure? (A bond involves one pair of electrons.) a) b) c) d) e) 10) Take one of the lone pairs off F and put it on H. Remove one of the lone pairs from F. Take one of the lone pairs of O and put it into the C-O bond, forming a double bond C=O. Take one of the C-F bonding pairs and make it a lone pair on C. Take one of the C-F bonding pairs and put it into the C-O bond, forming a double bond C=O. 1 3 5 7 8 H O H C C O H H The molecular geometry of PCl3 is a) b) c) d) e) CHE 106 linear bent (or angular) trigonal planar trigonal pyramidal tetrahedral 3 Fall 2005 Exam #3 11) The molecule of propenol has the bond structure at right. The hybridization on the three carbons, from left to right, is a) b) c) d) e) 12) H H–C–C=C–O-H H 1 and 2 1 and 3/2 2 and 3/2 2 and 5/2 2 and 3 The order of filling of molecular orbitals in homonuclear diatomics is as follows: 1s < *1s < 2s < *2s < 2p < 2p < *2p < *2p Derive the orbital diagrams for the following molecules: Be2, B2, and C2. Which of these three molecules are paramagnetic? a) b) c) d) e) 14) H The order of filling of molecular orbitals in homonuclear diatomics is as follows: 1s < *1s < 2s < *2s < 2p < 2p < *2p < *2p The molecule of C2 has 12 electrons. The bond orders in C2 and n the anion C2are a) b) c) d) e) 13) sp3, sp3, sp sp2, sp2, sp3 sp, sp2, sp3 sp2, sp, sp3 sp2, sp3, sp3 none of them just Be2 just B2 just C2 B2 and C2 Suppose 3.15 L of neon at 21°C and P = 0.951 atm is compressed to 1.292 atm, with the temperature held contant. The new volume is a) b) c) d) e) CHE 106 2.32 L 3.00 L 3.15 L 4.10 L 4.44 L 4 Fall 2005 Exam #3 15) A tank of volume 40 L contains a gas at 1.0 atm pressure, and a temperature of 20°C. Another tank, of volume 60 L, contains the same gas, also at 20°C, but at 2.0 atm pressure. The tanks are connected so gas can flow between them, with the temperature maintained at 20°C. At equilibrium, the pressure is the same everywhere in the total volume of 100 L. What is the final pressure? a) b) c) d) e) 16) What is the density of ammonia gas, NH3, at 31°C (304 K) and 0.988 atm pressure? Molar mass of NH3 is 17.03 g/mol. R = 8.314 J mol-1 K-1 = 0.0820 L atm mol-1 K-1. a) b) c) d) e) 17) 1.4 atm 1.5 atm 1.6 atm 2.0 atm 3.0 atm 0.0396 g/L 0.675 g/L 0.691 g/L 6.61 g/L 16.8 g/L Ammonium sulfate is produced by reacting ammonia with sulfuric acid, according to: 2NH3(g) + H2SO4(aq) (NH4)2SO4(aq). What volume of ammonia gas at 15°C and 1.15 atm is required to produce 1.136 mol of ammonium sulfate? a) b) c) d) e) CHE 106 11.7 L 20.5 L 23.4 L 40.6 L 46.7 L 5 Fall 2005 Exam #3 18) Here are three statements about the molecules in an ideal gas. I. The forces between molecules are almost always unimportant. II. The average speed of a molecule is proportional to the temperature. III. The kinetic energy of a molecule is unchanged if it collides with the container wall. Which of these statements are true, according to the kinetic-molecular theory of the ideal gas? a) b) c) d) e) 19) Which of the following is/are characteristic of gases? a) b) c) d) e) 20) High compressibility Relatively large distance between molecules. Formation of homogeneous mixtures regardless of the natures of nonreacting gas components. All of the above. None of the above. The average kinetic energy of molecules of a gas depends on a) b) c) d) e) 21) none of them number I and II number II and III number I and III all of them the temperature of the gas. the total mass of the molecules of the gas. the density of the gas. all of these. none of these. 24.2 g of gas initially at 4.00 atm is compressed from 8.00 L to 2.00 L at constant temperature. What is the resulting pressure (in atm) of the gas? a) b) c) d) e) CHE 106 4.00 2.00 1.00 8.00 16.0 6 Fall 2005 Exam #3 22) A sample of hydrogen was collected by water displacement at 23.0°C and an atmospheric pressure of 735 torr. Its volume is 568 mL. After water vapor is removed, what volume would the hydrogen occupy at the same conditions of pressure and temperature? (The vapor pressure of water at 23.0°C is 21 torr). a) b) c) d) e) 23) 509 mL 539 mL 552 mL 568 mL 585 mL Which one of the following is not possible for an ideal gas? a) V1 V2 T1 T2 b) V1T1 V2T c) V1 T1 V2 T2 d) V2 e) none of the above. T2 V2 T1 24) How many moles of gas occupy 60.82 L at 31°C and 367 mm Hg? a) b) c) d) e) CHE 106 1.18 0.850 894 11.6 0.120 7 Fall 2005 Exam #3