PRACTICE PROBLEMS FROM THE AMERICAN CHEMICAL SOCIETY…VSEPR &
STOICHIOMETRY
INDEX: P003
LEVEL: (A)
ANSWER: (D)
KEYWORDS: bonding, metals & nonmetals
ALTERNATIVE FORMAT: (TF)
are geometrically similar. Use each response in a
separate question.
Which pair is geometrically similar?
(A) SO2 and CO2
(C) CO2 and OF2
(B) PH3 and BF3
(D) SO2 and O3
NH3 (pyramidal geometry) reacts with BF3 (planar
geometry) to form the addition compound, H3NBF3. What
is the geometry around the nitrogen and boron centers in the
addition compound?
INDEX: P005
LEVEL: (A)
ANSWER: (A)
KEYWORDS: periodic properties, bonding
ALTERNATIVE FORMAT: (FR)
NH3 (pyramidal geometry) reacts with BF3 (planar geometry) to
form the addition compound, H3NBF3. What is the geometry
around the nitrogen and boron centers in the addition
compound? Explain in terms of the hybrid orbitals involved.
(A) Both centers are tetrahedral.
(B) Nitrogen–tetrahedral and boron–linear.
(C) Nitrogen–pyramidal and boron–planar.
INDEX: P009
LEVEL: (U)
KEYWORDS: bonding
ALTERNATIVE FORMAT: (FR)
The Lewis structure of BrF5 is
(D) Nitrogen–planar and boron–pyramidal.
The Lewis structure of BrF5 is
ANSWER: (A)
:F :
:F
:F :
:F
Br
:F :
F:
:F :
What is the shape of the molecule, and what is the orbital
hybridization of the Br atom?
INDEX: P011
LEVEL: (A)
ANSWER: (C)
KEYWORDS: bonding, periodic properties
ALTERNATIVE FORMAT: (TF)
is planar. Use each response in a separate question.
Br
:F :
F:
:F :
The molecular structure of BrF5 is
(A) square pyramidal.
(C) trigonal pyramidal.
(B) trigonal bipyramidal.
Which is planar?
(D) octahedral.
(A) PCl3
(C) CO32–
(E) PH3
(B) ClO3–
(D) NH3
INDEX: P022
LEVEL: (A)
ANSWER: (A)
KEYWORDS: bonding
ALTERNATIVE FORMAT: (FR)
Sulfur dioxide can be described by the structures:
Sulfur dioxide can be described by the structures:
: O ::
: O ::
S
:O :
:O
:S : :
O:
S
:O :
:O
:S : :
O:
This implies that
What does the figure imply about the bond lengths and
distribution of electrons in the molecule?
(A) the two bonds in SO2 are of equal length, and the
electronic distribution in the two SO bonds is identical.
(B) the single bond is longer than the double bond and the
electronic distribution in the two SO bonds is different.
(C) an electron pair in the SO2 molecule alternates back
and forth between the two sulfur–oxygen electron pairs so
that the two different bonds seem to exchange positions.
INDEX: P024
LEVEL: (U)
KEYWORDS: bonding
ALTERNATIVE FORMAT: (TF)
The bond angle of
is larger than that of
responses in separate questions.
ANSWER: (C)
(D) the SO2 molecule revolves so that the two different
bonds seem to exchange positions.
Which is the largest bond angle?
(A) angle O–S–O in SO42–
. Use pairs of
(B) angle Cl–C–Cl in HCCl3
(C) angle F–Be–F in BeF2
INDEX: P025
LEVEL: (U)
ANSWER: (D)
KEYWORDS: bonding, periodic properties
ALTERNATIVE FORMAT: (TF)
is a polar molecule. Use each response in a separate
question.
(D) angle H–O–H in H2O
Which molecule is polar?
(A) BF3
(B) CO2
(C) CF4
(D) H2S
The structure of the CO32 – ion can be described in the
Lewis formulation by the structures
INDEX: P039
LEVEL: (A)
ANSWER: (D)
KEYWORDS: bonding
ALTERNATIVE FORMAT: (TF)
The structure of the CO32 – ion can be described in the
Lewis formulation by the structures
2-
:O:
:O
C
O:
which means that
question.
2-
:O :
:O
C
O:
2-
:O :
:O
C
. Use each response in a separate
O:
2-
:O:
:O
C
O:
2-
:O :
:O
C
O:
2-
:O :
:O
C
O:
which means that
(A) two CO bonds are single bonds, the third CO bond is a
double bond.
(B) three independent forms of the CO32 – ion co-exist in
equilibrium.
(C) the electrons must be rapidly exchanging among the
three forms.
(D) the CO32 – ion exists in only one form which is a
composite or average of the three principal structures
shown.
INDEX: V001
LEVEL: (U)
KEYWORDS: formulas and equations,
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (B)
When an electric discharge is passed through boron trichloride
a new compound is formed. What is its simplest formula if
on analysis it is shown to contain 0.0878 g of chlorine and
0.0131 g of boron?
Atomic Molar Masses
B
Cl
(A) BCl
INDEX: V002
LEVEL: (U)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (A)
(B) BCl2
10.8 g·mol–1
35.5 g·mol–1
(C) BCl3
(D) B2Cl3
What is the empirical formula for the substance with this
analysis:
Elemental Analysis
Na
54.0%
B
8.50%
O
37.5%
Atomic Molar Masses
B
Na
O
(A) Na3BO3
INDEX: V006
LEVEL: (U)
ANSWER: (C)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
A compound of sodium, sulfur, and oxygen contains
29.1% Na, 40.6% S, ad 30.3% 0. What is the correct empirical
formula?
Atomic Molar Masses
Na
23.0 g·mol–1
S
32.1 g·mol–1
O
16.0 g·mol–1
INDEX: V009
LEVEL: (U)
ANSWER: (D)
KEYWORDS: formulas and equations, organic chemistry
ALTERNATIVE FORMAT: (SA)
Omit responses.
10.8 g·mol–1
23.0 g·mol–1
16.0 g·mol–1
(C) Na2B2O3
(B) Na4BO4
(D) NaB2O2
A compound of sodium, sulfur, and oxygen contains
29.08% Na, 40.56% S, and 30.36% 0. Which formula is
correct?
Atomic Molar Masses
Na 23.0 g·mol–1
S 32.1 g·mol–1
O 16.0 g·mol–1
(A) Na2SO3
(D) Na2S2O8
(B) Na2SO4
(E) Na2S4O6
(C) Na2S2O3
A gaseous compound contained 90% carbon and 10%
hydrogen by mass. What is the simplest formula for the gas?
Atomic Molar Masses
C 12.0 g·mol–1
H 1.0 g·mol–1
(A) CH4
(E) C9H2O
(B) C2H2
(C) C2H6
(D) C3H4
INDEX: V012
LEVEL: (U)
ANSWER: (A)
KEYWORDS: formulas and equations, organic chemistry
ALTERNATIVE FORMAT: (SA)
Omit responses.
INDEX: V032
LEVEL: (U)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (C)
The empirical (simplest) formula of a compound containing
54.53% carbon, 9.15% hydrogen, and 36.32% oxygen is
Atomic Molar Masses
C 12.0 g·mol–1
H 1.0 g·mol–1
O 16.0 g·mol–1
(A) C2H4O
(D) C4H8O2
(B) C4H9O2
(E) CHO
(C) C5H9O
The percent by mass of oxygen in Ca(NO3)2 is
Atomic Molar Masses
Ca 40.1 g·mol–1
N 14.0 g·mol–1
O 16.0 g·mol–1
(A)
16.0
 100
70.1
(D)
48.0
 100
102.1
(B)
96.0
 100
102.1
(E)
48.0
 100
164.1
96.0
 100
164.1
How many moles of Fe are needed to produce
10.0 mol of H2?
(C)
INDEX: V034
LEVEL: (U)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (A)
4H2O(g) + 3Fe(s)  Fe3O4(s) + 4H2(g)
(A) 7.50 mol
INDEX: V035
LEVEL: (U)
ANSWER: (D)
KEYWORDS: formulas and equations, environmental and
consumer chemistry
ALTERNATIVE FORMAT: (SA)
Omit responses.
(C) 15.0 mol
(B) 13.3 mol
(D) 30.0 mol
Assuming complete oxidation in the reaction
C(s) + O2(g)  CO2(g)
what mass of CO2 will 15 g of carbon produce?
Molar Masses
C
O2
CO2
(A) 11 g
(B) 22 g
12. g·mol–1
32. g·mol–1
44. g·mol–1
(C) 44 g
(D) 55 g
INDEX: V036
LEVEL: (U)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (C)
How many grams of aluminum chloride can one obtain from
6.00 mol of barium chloride?
Al2(SO4)3 + 3BaCl2  3BaSO4 + 2AlCl3
Atomic Molar Masses
Al
Cl
(A) 1250 g
INDEX: V037
LEVEL: (A)
KEYWORDS: formulas and equations
ALTERNATIVE FORMAT: (SA)
Omit responses.
ANSWER: (A)
(C) 534 g
(D) 134 g
If 0.50 mol of Na3PO4 is mixed with 0.30 mol of BaCl2, the
maximum number of moles of barium phosphate which can
be formed is
(A) 0.10
INDEX: V038
LEVEL: (A)
ANSWER: (B)
KEYWORDS: formulas and equations, environmental and
consumer chemistry
ALTERNATIVE FORMAT: (SA)
Omit responses.
(B) 801 g
27.0 g·mol–1
35.5 g·mol–1
(B) 0.15
(C) 0.30
(D) 0.50
How many moles of sulfur dioxide, SO2, can be produced
from 160 g of sulfur and 320 g of oxygen?
Atomic Molar Masses
S
O
(A) 2.5 mol (B) 5.0 mol
32. g·mol–1
16. g·mol–1
(C) 7.5 mol (D) 10.0 mol