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001 5.0 points Which of the following species is/are param- agnetic? I) Li− 2 II) O 2 III) H+ 2
- III only
- II and III
- I and III
- I only
- II only
- I and II
- I, II and III correct
Explanation: Li− 2 and H+ 2 both have an odd number of electrons and therefore must be paramag- netic. O 2 has 16 total electrons, the last two of which must go into separate degenerate π∗ anti-bonding orbitals.
002 5.0 points Rank the labeled bonds in the molecule
C
c
b N
bb
H
e
O
bb bb H (^) a
Sbbb^ b
d b b Sbb
H
from least to most polar.
- c < d < e < b < a
- c < d < e < a < b
- c < e < b < a < c
- d < c < e < b < a correct
- d < c < b < e < a
Explanation: Bonds a, b, c, d, and e have a ∆EN of 1.4, 1.0, 0.5, 0.0, and 0.9, respectively.
003 5.0 points A hypothetical rock was harvested from an- other planet. Trapped inside was a diatomic gas. A volume of 1.25 mL of the gas was ex- tracted from the rock at STP. The mass of the gas sample was determined to be 2.12 mg. Identify the gas.
- hydrogen
- nitrogen
- oxygen
- None of these
- fluorine correct
Explanation: The molecular weight is 37.99 grams per mole, thereby matching the weight of di- atomic fluorine.
004 5.0 points How many σ (sigma) and how many π (pi) bonds are there in the Lewis structure of the following organic molecule?
C
C
H H
C
bO b bb
b b Obb
H
H C C
- 10; 4 correct
- 14; 0
- 12; 0
- 10; 6
Explanation:
005 5.0 points Which of the following species is incorrectly paired with its strongest type of intermolecu- lar force?
- N 2 H 4 (hydrazine), hydrogen bonding
- O 3 (ozone), dispersion forces correct
- C 6 H 6 (benzene), dispersion forces
- NaCl (table salt), ionic bonding
Explanation: Ozone is polar and has dipole-dipole inter- actions.
006 5.0 points Rank the following species in terms of increas- ing bond length: N 2 , O− 2 , Ne+ 2 , H 2 , B^22 −.
- Ne+ 2 < H 2 < O− 2 < N 2 < B^22 −
- N 2 < O− 2 < B^22 − < Ne+ 2 < H 2
- Ne+ 2 < H 2 < B^22 − < O− 2 < N 2
- N 2 < B^22 − < O− 2 < H 2 < Ne+ 2 correct
- N 2 < O− 2 < H 2 < Ne+ 2 < B^22 −
Explanation: The species N 2 , O− 2 , Ne+ 2 , H 2 and B^22 − have bond orders of 3, 1.5, 0.5, 1 and 2, respec- tively. Bond length is inversely proportional to bond strength.
007 5.0 points Which of the molecules below will contain more than one σsp^2 ,sp^2 bond?
- CH 3 PHCH 3
- SiH 3 CHCHCHO correct
- CH 2 SF 2
- CF 3 CHCHCBr 3
Explanation: Both SiH 3 CHCHCHO and CF 3 CHCHCBr 3 contain a σsp^2 ,sp^2 bond (the C=C bond), but SiH 3 CHCHCHO contains an additional σsp^2 ,sp^2 bond between C and O.
008 5.0 points Which of the following statements regarding intermolecular forces (IMF) is/are true? I) Intermolecular forces result from attrac- tive forces between regions of positive and negative charge density in neighbor- ing molecules. II) The stronger the bonds within a molecule are, the stronger the intermolecular forces will be. III) Only non-polar molecules have instanta- neous dipoles.
- II only
- III only
- I and III
- I, II, and III
- II and III
- I and II
- I only correct
Explanation: Statement I is true - all IMF result from Coulombic attraction. Statements II and III are both false; the strength of the bonds within a molecule have no bearing on the strength of the bonds between molecules; all molecules have London forces.
009 5.0 points Which of the following molecules would have the smallest a and b term, respec- tively, in the van der Waals’ equation: O 3 , CHF 3 , SF 5 Cl, SiHCl 3 , Xe.
Explanation: Statement I is false because bonding or- bitals are lower in energy than their corre- sponding anti-bonding orbitals. Statement III is false, because degenerate molecular or- bitals are half-filled before being completely filled, according to Hund’s rule, just like atomic orbitals.
013 5.0 points Which of the following is polar?
- SF 4 correct
- XeF 4
- ICl− 4
- SF 6
- AsF− 6
Explanation: XeF 4 and ICl− 4 have 6 RHED with two RHED being lone pairs on the central atom situated opposite each other so their effects cancel. The others have 5 or 6 RHED and no lone pairs. Only SF 4 has an unbalanced number of lone pairs which places one of the polar S-F bonds opposite a lone pair. This unopposed dipole and the lone pair itself make it polar.
014 5.0 points Rank the following species from strongest to weakest bonds based on bond order: O 2 , N+ 2 ,
H− 2 , Li 2 , C^22 −.
- C^22 − > N+ 2 > O 2 > H− 2 > Li 2
- N+ 2 > O 2 > C^22 − > H− 2 > Li 2
- C^22 − > N+ 2 > O 2 > Li 2 > H− 2 correct
- N+ 2 > O 2 > C^22 − > Li 2 > H− 2
- N+ 2 > C^22 − > O 2 > Li 2 > H− 2
Explanation: The species O 2 , N+ 2 , H− 2 , Li 2 and C^22 − have
bond orders of 2, 2.5, 0.5, 1 and 3 respectively.
015 5.0 points Which of the following statements about gas laws is/are true? I) Amedeo Avogadro determined that there was a direct proportionality between number of moles and volume of a gaseous system. II) The ideal gas law assumes gas molecules collide elastically with the walls of their container. III) The ideal gas constant has the same value for all gases.
- II only
- I, II, III correct
- II, III
- I, II
- III only
- I only
- I, III Explanation: All three statements are true. Avogadro’s law states that adding matter to a gaseous system will increase its volume. The ideal gas law assume the conditions of kinetic molec- ular theory are met, one of which is elas- tic collisions between gas molecules and their container. R is a constant.
016 5.0 points What would be the electron geometry of the nitrogen atom in nitric oxide, N 2 O?
- trigonal planar
- trigonal bipyramidal
- octahedral
- linear correct
- tetrahedral
Explanation: The central nitrogen atom in N 2 O has only 2 regions of electron density.
017 5.0 points Which one of the following substances is IN- CORRECTLY matched with the kind of solid that it forms?
- calcium bromide : ionic
- sulfur dioxide : molecular
- methane : molecular
- graphite : covalent
- lithium : covalent correct
Explanation: Molecular solids consist of molecules held together by weak intermolecular forces. Ionic solids are held together by electro- static attraction between metal cations and non-metal anions. Metallic solids consist only of metals held together by metallic bonds. Covalent (or network) solids are like huge molecules held together by covalent bonds. Carbon in diamond is the most well-known example. Group IV B elements can form tetrahedral electronic geometries. Lithium will form a metallic solid.
018 5.0 points Choose the species below that exhibits delo- calization.
- CO 2
- NH 4 +
- NO 2 −^ correct
- H 2 O
- H 3 O+
Explanation:
Both of the bonds CO 2 are double bonds
- there is no resonance, and so no delocal- ization. The species NH 4 +, H 2 O, and H 3 O+ all have only single (σ) bonds, and so can- not exhibit delocalization. The nitrite anion is all that remains and does in fact exhibit delocalization.
019 5.0 points In which of the following do the unbonded electron pairs not distort the bond angles?
- H 2 O
- NH 3
- I 3 −^ correct
- SF 4
- O 3
Explanation: All of the choices except I− 3 have asymmet- rically placed non-bonding electron pairs on their central atoms and thus have distorted bond angles. I− 3 has three non-bonding elec- tron pairs in equatorial positions and thus has a single bond angle of exactly 180◦.
020 5.0 points Which of the following is not correctly paired with its dominant type of intermolecular forces?
- CaO, ionic forces
- C 6 H 6 (benzene), instantaneous dipoles
- NH 3 , hydrogen bonding
- HBr, hydrogen bonding correct
- SiH 4 , instantaneous dipoles
Explanation: London forces, dispersion forces, van der Waals’ forces, instantaneous or induced dipoles all describe the same intermolecular force. London forces are induced, short-lived,
greater than for S-H or Se-H. H 2 O exhibits H-bonding, so it has the highest boiling point of the three compounds. The relative polar- ities (∆EN) of the H 2 Se and H 2 S bonds are similar and one would predict slightly smaller for H-Se based on general trends, so dipole- dipole interactions do not explain the trend. However, London interactions become longer as the size of the molecule’s electron cloud in- creases; since Se is bigger than S, H 2 Se has stronger London forces and thus a higher boil- ing point than H 2 S.
024 5.0 points Which of the following statements concerning hybrid orbitals is/are true? I) Hybrid orbitals are energetically degen- erate. II) Any element can form sp^3 d^2 hybrid or- bitals. III) Hybridizing a 2s and a 2p orbital would produce one single sp hybrid orbital.
- II only
- II, III
- III only
- I, II
- I, II, III
- I only correct
- I, III
Explanation: Statement I is true; hybridization was de- veloped as a theoretical framework to ex- plain the energetic degeneracy of bonds in molecules. Statement II is false; hybridiza- tion involving d orbitals requires access to empty d orbitals, and thus begins in period
- Statement III is false; the number of or- bitals used to hybridize is always equal to the number of hybridized orbitals, so using a 2s and a 2p orbital would result in two sp hybrid orbitals.
025 5.0 points Helium has a rms velocity (vrms) that is 4. times faster than which of the following gases?
- chlorine, Cl 2 correct
- xenon, Xe
- argon, Ar
- neon, Ne
- oxygen, O 2 Explanation: The relationship of rms velocities between different molecules is:
rateA rateB
massB massA
Let massA be helium’s mass of 4.0 and 4. be heliums rate so that:
- 21 1
massB
- 0
(4.21)^2 =
massB
- 0 70 .9 = massB
This only matches the chlorine gas, Cl 2.
026 5.0 points During vaporization of water which of the following statements is not true?
- The bubbles that form before the water reaches its boling point are primarly air.
- Boiling involves the disruption of hydro- gen bonds.
- Intermolecular bonds are broken during the vaporization process.
- Intramolecular bonds are broken during the vaporization process. CORRECT
Explanation: Vaporization requires disrupting hydrogen bonds, which are intramolecuar, not inter- molecular. Before water reaches its booiling
point, any dissolved gases come out of solu- tion; these are the small bubbles that form early on when heating water.
027 5.0 points For the reaction
2 HCl + Na 2 CO 3 → 2 NaCl + H 2 O + CO 2
179.2 liters of CO 2 is collected at STP. How many moles of NaCl are also formed?
- 16.0 moles correct
- 4.0 moles
- 12.5 moles
- 8.0 moles
- 6.0 moles
- 32.0 moles
Explanation: VCO 2 = 179.2 L
At STP we can use the standard molar volume, 22.4 L/mol.
179 .2 L 22 .4 L/mol
= 8.00 mol CO 2
8 .00 mol CO 2 ×
2 mol NaCl 1 mol CO 2
= 16.0 mol NaCl
028 5.0 points Which is the most polar molecule?
- Ar
- H 2 O correct
- CH 4
- CF 4
- CO 2
- BF 3
Explanation:
H 2 O has angular molecular geometry. It is assymetrical and polar.
029 5.0 points Consider the following molecular orbital dia- gram:
a
b
c
What are the names of the labeled orbitals, a, b, and c, respectively?
- σ 2 ∗p, π 2 p, σ∗ 2 s
- σ 2 ∗p, π 2 p, σ∗ 1 s
- σ 2 ∗p, π 2 p, σ 2 s correct
- π 2 ∗p, σ 2 ∗p, σ 2 s
- π 2 ∗p, σ 2 p, σ∗ 2 s
Explanation:
030 5.0 points Rank the compounds
NH 3 , N 2 , C 2 H 6 , NCl 3 , H 2
in terms of decreasing capillary action in a glass tube.
- NH 3 , NCl 3 , C 2 H 6 , N 2 , H 2 correct
- NH 3 , C 2 H 6 , N 2 , NCl 3 , H 2
- H 2 , N 2 , C 2 H 6 , NCl 3 , NH 3
- NCl 3 , C 2 H 6 , N 2 , NH 3 , H 2
- NH 3 , N 2 , C 2 H 6 , NCl 3 , H 2
