CHEM 207
(A)
1. Midterm Exam
11.11.2010
Name:
Student Number:
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1) The __________ tells us that each orbital can hold a maximum of 2 electrons.
A) Pauli exclusion principle
B) uncertainty principle
C) aufbau principle
D) Hund's rule principle
E) LeChatelier principle
2) Provide a Lewis structure for a molecule with molecular formula CH2O2.
1) _______
2) _____________
3) Write a Lewis structure for a compound with the molecular formula H2N2.
4) The compound methylamine, CH3NH2, contains a CN bond. In this bond, which of the
4) _______
following best describes the charge on the carbon atom?
A) +1
B) slightly positive
C) uncharged
D) slightly negative
E) -1
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5) The electronegativity of elements on the periodic table increases going __________ a column and
to the __________ in each row.
A) up, left
B) down, left
C) down, right
D) up, right
5) _______
6) Which of the following are correct Lewis structures, including formal charges, for nitric acid,
HNO3?
6) _______
A)
B)
C)
D)
E)
A only
B only
C only
both B and C
A, B, and C
7) One resonance structure of a cation is shown. Provide the other reasonable resonance
structures.
7) _____________
8) Provide the structural Formula (showing all bonds) for an aldehyde whose condensed
structure is (CH3)3CCHO.
8) _____________
9) Provide the line-angle formula for the alcohol CH3CH2CH(OH)CH2CH2CH(CH3)2.
9) _____________
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10) Provide the products of the following acid-base reaction.
10) _____________
(CH3)3NH+ + HO-→
11) When methanol (CH3OH) acts as a base, its conjugate acid is __________.
A) -CH2OH
11) ______
B) CH4O+
C) CH3OH2+
D) CH3OE) CH4OH
12) Which of the following pairs of bases lists the stronger base first?
A) H2O > HOB) CH3COO- > HO-
12) ______
C) HO- > H2ND) I- > ClE) H2N- > CH3COO13) Consider the species CH3O-, NH2-, and CH3COO-. Rank these ions in order of increasing basicity, and
explain your rationale.
14) Complete the following chemical reaction and predict whether the equilibrium will
favor the reactants of products . Briefly explain why:
14) _____________
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15) Which atomic orbital combination would result in a molecular sigma bond?
A)
B)
C)
15) ______
D)
16) Consider the interaction of two hydrogen 1s atomic orbitals of the same phase. Which of the
statements below is an incorrect description of this interaction?
A) The molecular orbital formed is cylindrically symmetric.
B) A sigma bonding molecular orbital is formed.
C) The molecular orbital formed has a node between the atoms.
D) A maximum of two electrons may occupy the molecular orbital formed.
E) The molecular orbital formed is lower in energy than a hydrogen 1s atomic orbital.
16) ______
17) Based on the structure below, what is the value for the H-N-CH3 bond angle? Briefly explain
17) ______
why.
A) 109 degrees
B) 90 degrees
C) 60 degrees
D) 120 degrees
18) In the structure below, the sigma bond of the carbonyl is formed from the overlap of a(n)
__________ orbital of carbon and a(n) __________ orbital of oxygen.
A) sp2, sp2
B) sp, sp2
19) Show the bonding scheme for the molecule below.
C) p, p
18) ______
D) sp3, sp2
19) ______
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20) What intermolecular forces are present among molecules in dimethyl ether, CH3OCH3?
A)
B)
C)
D)
20) ______
both London dispersion forces and dipole-dipole forces
London forces only
both London dispersion forces and hydrogen bonding
hydrogen bonding only
21) Which of the molecules below has the higher boiling point? Briefly explain your choice.
CH3CH2CH2OH
or
CH3CH2OCH3
22) Which of the molecules below has the higher boiling point? Briefly explain your choice.
CH3CH2CH2CH2CH3
or
(CH3)2CHCH2CH3
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1) A
2)
3)
4) B
5) D
6) B
7)
8)
9)
10) (CH3)3N + H2O
11) C
12) E
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13) CH3COO- < CH3O- < NH2The first factor to consider is the nature of the atom which bears the negative charge. The more electronegative the
atom that bears the negative charge, the more stable the anion. Stable anions are less reactive and are hence weaker
bases. Since O is more electronegative than N, the NH2- is the strongest base in the set. In the remaining two
species, the negative charge is on the O, but in the case of CH3COO-, the negative charge is also delocalized by
resonance.
14)
15)
16)
17)
18)
19)
20)
21)
The stronger acid and the stronger base are both on the left side of the reaction (reactants); therefore, the
equilibrium concentration should favor the products or right side of this equation.
B
C
D
A
B
A
CH3CH2CH2OH has the higher boiling point since it is capable of intermolecular hydrogen bonding.
22) CH3CH2CH2CH2CH3 has the higher boiling point. As the degree of branching increases, the surface area of the
molecule decreases and the potential for intermolecular attraction via London forces decreases. Greater surface area
leads to a more intermolecular attraction which in results in a higher boiling point.
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