combinepdf-2.pdf - CHEM 230 W16 PREP Final Exam KEY p1 14a...

CHEM 230 W16 PREP Final Exam KEY p1
14a) Carbonated water is prepared by cooling water to 8.0
o
C and pressurizing water with a P
CO2
of
8.3 bar. I wanted to find the solubility of CO
2
at this temperature, but I could not find a value for
k
H
(the Henry's law constant) at 8.0 o C. However, I found the mole fraction of CO
2
in water
water to be 0.002771 at 8.0 o C when the partial pressure of CO
2
was 8.3 bar. What is the
solubility (molarity) of carbon dioxide under these conditions given a solution density of 0.997g/mL?
pick 100 moles total:
0.002771 =
molCO
2
mol total
=
mol CO
2
100
0.2771 molCO
2
44 gCO
2
1 molCO
2
"
#
$
%
&
'
= 12.19 gCO
2
100 − 0.2771 = 99.723 molH
2
O
18 gH
2
O
1 molH
2
O
"
#
$
%
&
'
= 1795 gH
2
O
Total g = 12.19 + 1795 = 1807.1 g total
1 mL solution
0.997g total
"
#
$
%
&
'
1 L
1000 mL
"
#
$
%
&
' = 1.812 L
M =
molCO
2
Lsolution
"
#
$
%
&
' =
0.2771 mol
1.812 L
"
#
$
%
&
' = 0.153 M CO
2
b) Based on the solubility that you found in part a, what is k
H
for CO
2
in water at 8 o C?
[CO
2(aq)
] M
0.153
s = k
H
P
CO
2
0.153
mol
L
= k
H
(8.3 bar )
0.0184
mol
Lbar
= k
H
k
H
mol/(L bar)
0.0184
If the CO
2(g)
above the water is removed and replaced by air (N
2(g)
and O
2(g)
) at a pressure of 8.3bar,
how will each of the following quantities change as the system goes to equilibrium?
Circle one answer in each box.
c) The [O
2
]
aq
will: increase decrease stay the same
d) The partial pressure of CO
2(g)
will: increase decrease stay the same
15
5
5
5
-3 mistake plugging in or math
-3 per math/transcription
0.355 = 4 pts total
-5 per conceptual mistke

CHEM 230 W16 PREP Final Exam KEY p2
15) Three different bases are titrated with 0.1M HCl as described below. Compare the titrations and
select the one that best matches the description in parts a-d. Check one column for each row.
10 mL, 0.2 M
NH
2
OH
pK
b
= 7.97
10 mL, 0.2 M
NH
2
NH
2
pK
b
= 5.77
10 mL, 0.2 M
CH
3
NH
3
pK
b
= 3.44
b) highest volume of 0.1 M HCl to
reach the stoichiometric point
All are
the same
c) lowest pH @ 1/2 stoichiometric point
d) highest pH at the stoichiometric point
X
X
X
20
16) a) What is the minimum number of grams of Pb(NO
3
)
2
(MW= 331.21) that must be added to 100
mL of 5.4x10 -4 M Na
2
SO
4
in order to observe a precipitate? (K
sp
PbSO
4
= 2.53x10 -8 )
PbSO
4(s)
--> Pb +2
(aq)
+ SO
4
2-
(aq)
K
sp
= 2.53x10 -8
K
sp
= [ Pb 2 + ][ SO
4
− 2 ]
2.53 x 10 − 8 = [ Pb 2 + ](5.4 x 10 − 4 )
4.68 x 10 − 5 = [ Pb 2 + ]
4.68 x 10 − 5 molPb + 2
L
0.1 L
#
$
%
&
'
(
1 molPb ( NO
3
)
2
1 molPb + 2
#
$
%
&
'
(
331.21 gPb ( NO
3
)
2
1 moPb ( NO
3
)
2
#
$
%
&
'
(
= 1.552 x 10 − 3 g
Pb(NO
3
)
2
g
1.552x10 -3
10
20
For a saturated aqueous solution of PbSO
4
, describe the response to each of the following stresses.
b) adding PbSO
4(s)
: PbSO
4(s)
will: dissolve precipitate neither cannot determine
c) adding NaNO
3(s)
: PbSO
4(s)
will: dissolve precipitate neither cannot determine
d) adding NaNO
3(aq)
: PbSO
4(s)
will: dissolve precipitate neither cannot determine
e) adding Pb(NO
3
)
2(aq)
: PbSO
4(s)
will: dissolve precipitate neither cannot determine
(Circle one answer in each box.)
a) highest initial pH
X
3 pts Ksp
4 pts [Pb+2]
3 pts conversion to g

CHEM 230 W16 PREP Final Exam KEY p3
Ti
(s)
Cl
2(g)
TiCl
4(l)
Δ H o
f
(kJ/mol) S o
m
(J/K mol)
30.7
223.07
-804.16
221.93
0
a) Write out the balanced chemical equation for the
formation of TiCl
4(l)
.