Download Problem Set #2 Answer Key

CHEM 10050
Supplemental Problem Set #2
1. Draw Lewis Structures and predict the molecular geometry for the following
molecules. Also, label each formula as “ionic, polar covalent or non-polar covalent”.
a) CH2O
b) HCN
c) NaBrO3
O
O
Na
+
O
C
H
H
trigonal planar
polar covalent
d) K3PO4
Br
O
H
C
N:
linear
polar covalent
pyramidal
ionic
e) C2H2
f) HSCN
3
K
K+
K
O
+
H
O
P
+
O
H
C
C
C
N
H
linear
non-polar covalent
O
S
bent linear
polar covalent
tetrahedral
ionic
g) SO3
h) CH3NO
O
C
O
S
O
i) HCNO
O
trigonal planar
non-polar
H
N
trigonal
planar
H
H
pyramidal
H
C
N
O
linear
polar covalent
polar
2. 25.0 g of butane (C4H10) was burned in a combustion reaction. How many grams of
carbon dioxide were produced?
2C4H10 + 13O2  8CO2 + 10H2O
25.0 g butane x
8 mol CO2
44.0 g CO2
1mol butane
x
x
 75.7 g CO2
58.12 g butane 2 mol butane 1mol CO2
3. 12.56 g of nitric acid was reacted with sodium carbonate in a double displacement
reaction. How many grams of carbon dioxide were produced?
Na2CO3 + 2HNO3  CO2 + H2O + 2NaNO3
12.56 g Na 2CO3 x
1 mol HNO3
1 mol CO2
44.01 g CO2
x
x
 4.396 g CO2
63.01 g HNO3 2 mol HNO3
1 mol CO2
4. The Haber Process for the synthesis of ammonia involves the reaction of hydrogen
gas with nitrogen gas in a combination reaction. How many grams of hydrogen gas
is needed to produce 50.0 g of ammonia?
3H2 + N2  2NH3
50.0 g NH3 x
1mol NH3
3 mol H2 2.016 g H2
x
x
 8.88 g H2
17.03 g NH3 2 mol NH3
1mol H2
5. Chlorine gas reacts with aluminum bromide in a single displacement reaction. How
many milliliters of bromine would be produced from 125.0 g of aluminum bromide?
(dBr2 = 3.14 g/ml)
2AlBr3 + 3Cl2  2AlCl3 + 3Br2
125.0 g AlBr3 x
1mol AlBr3
3 mol Br2
159.8 g Br2
1ml Br2
x
x
x
 35.8 ml Br2
266.69 g AlBr3 2 mol AlBr3
1mol Br2
3.14 g Br2
6. Balance the following equations. Identify the redox reactions and label the reducing
and oxidizing agents.
a) Na(s) + H2O(l) H2(g) + NaOH(aq)
2Na(s) + 2H2O(l) H2(g) + 2NaOH(aq)
Na – reducing agent
H2O – oxidizing agent
b) H3PO4(aq) + NaOH(aq) H2O(l) + Na3PO4(aq)
H3PO4(aq) + 3NaOH(aq)  H2O(l) + Na3PO4(aq)
Not a redox reaction!
c) Al(s) + H2SO4(aq)  H2(g) + Al2(SO4)3(aq)
2Al(s) + 3H2SO4(aq)  3H2(g) + Al2(SO4)3(aq)
Al – reducing agent
H2SO4 – oxidizing agent
7. Calculate the volume that would be occupied by 12.0 g carbon dioxide at 720 torr
and 28°F.
PV = nRT
1mol CO2
1 atm
 0.947 atm
P = 720 torr x
n  12.0 g CO2 x
 0.273 mol CO2
760 torr
44.0 g CO2
R = 0.0821
L  atm
mol  K
T=
28 o F  32
 273  271K
1.8
L  atm 

(0.273 mol CO 2 ) 0.0821
(271 K)
nRT
mol  K 

V

 6.41L
P
(0.947 atm)
8. How many grams of acetylene (C2H2) are contained in a 60 L gas cylinder at
1,650 psi and 73°F?
PV = nRT
V = 60 L
R = 0.0821
P = 1,650 psi x
L  atm
mol  K
1 atm
 112 atm
14.7 psi
73 o F  32
 273  296 K
1.8
PV
(112 atm)(60 L)
n

 277 mol C2H2
L  atm 
RT 
 0.0821
(296 K )
mol  K 

T=
277 mol C2H2 x
26.04 g C2H2
 7.20 x 103 g C2H2
1mol C2H2
9. 6.75 g of oxygen gas occupies a volume of 3.25 L at 740 torr. What is the Celsius
temperature of this gas?
PV = nRT
V = 3.25 L
n  6.75 g O2 x
P = 740 torr x
1mol O2
 0.211mol O2
32.0 g O2
T
PV

nR
1 atm
 0.974 atm
760 torr
L  atm
R = 0.0821
mol  K
(0.974 atm)(3.25 L)
 183 K
L  atm 

(0.211mol O 2 ) 0.0821

mol  K 

10. Draw two resonance forms for the following molecules. Indicate which, if any,
resonance form contributes most to the bonding description for the molecule. (Hint:
use formal charges)
a. CS2
S
C
S
S
contributes most
C
S
contributes least
b. HN3
H
N
N
N
H
N
N
2
N
H
N
N
11. Define and describe the three basic types of van der Waal’s forces.
See Notes
12. Determine formulas from the following names:
a) phosphorus pentachloride
PCl5
b) iodine heptafluoride
IF7
c) tetraphosphorus decasulfide
P4S10
d) selenium hexafluoride
SeF6
e) dinitrogen tetraoxide
N2O4
13. Write an equation for the complete ionization of the following compounds:
a) sulfuric acid
b) nitric acid
H2SO4  2H+ + SO42
HNO3  H+ + NO3
c) calcium hydroxide
Ca(OH)2  Ca2+ + 2OH
d) aluminum sulfate
Al2(SO4)3  2Al3+ + 2SO42
e) phosphoric acid
H3PO4  3H+ + PO43
N
14. Balance the following chemical equations and identify each as addition,
decomposition, single displacement, double displacement or combustion.
a.
Au2O3 
Au +
O2
2Au2O3  4Au + 3O2
decomposition
b.
Mg
Fe3O4 
+
Fe
4Mg
c.
FeCl2
FeCl2
d.
H3PO4
+
Fe(OH)2
+
4MgO
NaCl
2NaOH  Fe(OH)2
double displacement
Ca(OH)2 
2H3PO4
e.
+
MgO
Fe3O4  3Fe +
single displacement
+
NaOH 
+
+
Ca3(PO4)2
+
+
H2O
+ 3Ca(OH)2  Ca3(PO4)2 +
double displacement (neutralization)
Cd(NO3)2 + H2S 
CdS
+
g.
C3H8O
KBr
+
+
O2 
CO2
2C3H8O
+
Cl2 
KCl
2KBr
+
2HNO3
H2O
9O2  6CO2
combustion
+
6H2O
HNO3
Cd(NO3)2 + H2S  CdS +
double displacement
f.
2NaCl
+
8H2O
Br2
+ Cl2  2KCl +
single displacement
Br2