1.
[7 points] It takes 0.098 g of silver iodate, AgIO3, to make 1.00-L of a
saturated solution saturated at 25 °C. What is the value of the solubility
product, Ksp?
a.
b.
c.
d.
e.
2.
[7 points] The Ksp for PbCl2 is 1.7 × 10–5. Determine the molar solubility of
PbCl2?
a.
b.
c.
d.
e.
3.
0.068 M
4.1 × 10–3 M
2.9 × 10–3 M
0.016 M
0.026 M
[7 points] What is the molar solubility of PbI2 (Ksp = 2.5 × 10–7) in a 0.100 M
NaI solution?
a.
b.
c.
d.
e.
4.
3.5 × 10–4
1.2 × 10–7
9.8 × 10–2
9.6 × 10–3
1.6 × 10–9
2.5 × 10–5 M
6.2 × 10–6 M
2.5 × 10–6 M
4.0 × 10–3 M
None of the above
[7 points] Which of the following reagents would decrease the solubility of
AgCl(s)?
NaOH
a.
b.
c.
d.
e.
HCl
NH3
NaCN
NH3
NH3 & NaCN
NaOH & NH3
HCl
None of these reagents will decrease the solubility of AgCl(s)
5.
[7 points] Given the fact that Ksp = 6.7 × 10–31 for Cr(OH)3, and that the
formation constant for the complex ion, Cr(OH)4–, is Kf = 8.0 × 1029. What is
the concentration of the complex ion Cr(OH)4– in a solution that is buffered at
pH = 11 and is in equilibrium with solid Cr(OH)3?
a.
b.
c.
d.
e.
6.
2.1 × 10–12
1.1 × 10–10
6.1 × 10–14
2.8 × 10–12
1.3 × 10–14
[7 points] An amphoteric oxide (i.e. ZnO) is an oxide that ___________.
a.
b.
c.
d.
e.
8.
× 10-5
× 10+26
× 10+2
× 10-4
× 10-7
[7 points] What is the concentration of free Ni2+, if 1.83 g of Ni(NO3)2 is
dissolved in 1.00 L of 3.0 M NH3 solution? [The formation constant for the
formation of the complex ion Ni(NH3)62+ is 1.2 × 109.]
a.
b.
c.
d.
e.
7.
2.8
8.0
5.4
5.4
3.8
Dissolves in strongly acidic solution, but not strongly basic solution
Dissolves in strongly basic solution, but not strongly acidic solution
Dissolves in both strongly acidic and strongly basic solutions
Only dissolves when the pH is nearly neutral
Sleeps with both metals and nonmetals
[7 points] In the laboratory you add 0.25 g of Ca(OH)2 to 500 mL of H2O and
stir the solution. After 2 minutes the solid has completely dissolved. The
solution is then divided into three beakers. To each of these beakers you add
100 mL of the following solutions:
Beaker 1: 100 mL of 6 M HCl solution
Beaker 2: 100 mL of 6 M NaCl solution
Beaker 3: 100 mL of 6 M CaCl2 solution
This leads to the formation of a white precipitate in which of the beakers?
a.
b.
c.
d.
e.
Beaker 1
Beaker 2
Beaker 3
Beakers 1 & 2
Beakers 1, 2 & 3
9.
[7 points] A solution contains three cations with the following concentrations,
0.10 M Cr3+, 1.50 M Cu2+ and 2.00 M Cd2+. If a dilute NaOH solution is slowly
added to the solution what is the first precipitate to form: Cr(OH)3 (Ksp = 1.6 ×
10-30), Cu(OH)2 (Ksp = 4.8 × 10-20), or Cd(OH)2 (Ksp = 2.5 × 10-14)?
a.
b.
c.
d.
Cr(OH)3
Cu(OH)2
Cd(OH)2
All three precipitates will begin to form when the first drop of NaOH is
added
10. [7 points] The Ksp for AgIO3 is 3.1 × 10–8. When 50 mL of 0.010 M AgNO3
solution is mixed with 10 mL of 0.015 M NaIO3 solution will a precipitate form?
a.
b.
c.
d.
e.
No, because Q = 2.1 × 10-5 and since it is larger than Ksp no precipitate will form
Yes, because Q = 2.1 × 10-5 and since it is larger than Ksp a precipitate will form
No, because Q = 1.5 × 10-4 and since it is larger than Ksp no precipitate will form
Yes, because Q = 1.5 × 10-4 and since it is larger than Ksp a precipitate will form
Not enough information is given to answer this question
11. [7 points] A solution that contains one or more of the following ions Ag+, Sn4+,
Ni2+, Fe3+, Cu2+ is subjected to the following steps:
Step
Action
Result
1
Add NaCl solution
A white precipitate forms (ppt A), which is
separated from a green decantate (soln 1)
2
Add HCl and H2S to soln 1
A yellow precipitate forms (ppt B), which is
separated from a green decantate (soln 2)
3
Add 3 M NaOH solution to ppt
B
The precipitate dissolves to form a colorless
solution
4
The pH of soln 2 is made basic
by adding 3 M NH3 solution and
buffering with NH4Cl
The color of the solution changes from green to
blue, no precipitate forms
Which cations are present in the solution?
a.
b.
c.
d.
e.
Sn4+, Cu2+ and Ni2+
Sn4+ and Ni2+
Ag+, Sn4+ and Ni2+
Ag+, Sn4+, Cu2+ and Ni2+
Ag+, Sn4+ and Cu2+
12. [7 points] You are given a solution and told that it contains two cations. To
test for the identity of the cations you add 15 M NH3 and 3 M NH4Cl. This
causes the solution to turn pink and leads to the formation of a white
gelatinous precipitate. From the choices below which two cations are most
likely to be present in the solution?
a.
b.
c.
d.
e.
Fe3+ and Co2+
Zn2+ and Ni2+
Al3+ and Co2+
Al3+ and Cr3+
Zn2+ and Co2+
13. [7 points] What of the following sulfides is white?
a.
b.
c.
d.
e.
CoS
ZnS
NiS
PbS
SnS2
14. [7 points] What reagent(s) could be used to separate Sb2S5 from CuS?
a.
b.
c.
d.
e.
HCl (aq)
H2SO4 (aq)
K2Cr2O7 (aq)
NaOH (aq)
CH3CSNH2 (aq) + heat
15. [7 points] How could you separate PbCl2 from AgCl?
a.
b.
c.
d.
e.
Add the solids to water and heat
Add the solids to a concentrated NH3 solution
Add the solids to a concentrated HCl solution
Add the solids to a K2Cr2O7 solution
Either (a) or (b) could be used to separate the two
16. [7 points] A solution that contains one or more of the following ions Cu2+, Fe3+,
Pb2+, Al3+ and Sb5+ is subjected to the following steps:
Step
Action
Result
1
The acidity of the solution was
adjusted to a pH = 0.4 with
HNO3, thioacetamide
(CH3CSNH2) was added and the
solution was heated
A dark precipitate forms (ppt A), which is
separated from a colorless decantate (soln 1)
2
Add 3 M NaOH solution to ppt
A
There is no apparent change in the precipitate
(ppt B), which is separated from a colorless
decantate (soln 2)
3
Add 6 M HNO3 solution to ppt
B
The precipitate dissolves to form a colorless
solution (soln 3)
4
Add 9 M H2SO4 to soln 3
A white precipitate forms (ppt C) and the
solution remains colorless
5
3 M HCl is added to soln 2 to
make the solution slightly
acidic
Nothing happens,
6
NH3 and NH4Cl are added to
the solution from step 5 until it
becomes basic
A white precipitate forms. The solution remains
colorless
Which cations are present in the solution?
a.
b.
c.
d.
e.
Pb2+, Sb5+ and Al3+
Cu2+ and Fe3+
Pb2+ and Cu2+
Pb2+ and Al3+
It’s not possible to definitely identify the cations present from these
observations
17. [7 points] Which of the following hydroxides is not amphoteric?
a.
b.
c.
d.
e.
Fe(OH)3
Cr(OH)3
Al(OH)3
None of these hydroxides is amphoteric
All of these hydroxides are amphoteric
18. [7 points] Which of the following statements is false?
a. Spontaneous processes are always irreversible
b. ΔG is always negative for a spontaneous process
c. ΔSsystem is always positive for a spontaneous process
d. A spontaneous process may be exothermic or endothermic
19. [7 points] For which of the following reactions would you expect ΔSrxn to be
positive?
a. 2SO2(g) + O2(g) → 2SO3(g)
b. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
c. Hg(l) → Hg(s)
d. CaO(s) + CO2(g) → CaCO3 (s)
e. None of the above reactions will have a positive ΔS
For problems 20 and 21 consider the reaction depicted below (all molecules shown are in
the gas phase):
Reactants
Products
20. [7 points] Predict the sign of ΔHrxn and ΔSrxn for the reaction shown above.
a.
b.
c.
d.
ΔSrxn
ΔSrxn
ΔSrxn
ΔSrxn
is
is
is
is
positive, ΔHrxn is positive
negative, ΔHrxn is positive
positive, ΔHrxn is negative
negative, ΔHrxn is negative
21. [7 points] What general statement can you make about the relationship
between spontaneity and temperature for the reaction shown above.
a.
b.
c.
d.
e.
The reaction is spontaneous at all temperatures
The reaction is not spontaneous at any temperature
The reaction becomes more spontaneous as the temperature decreases
The reaction becomes more spontaneous as the temperature increases
There is not enough information given to answer this question
Use the following standard thermodynamic quantities as appropriate to answer
problems 22-24.
Compound
ΔHfº
(kJ/mol)
ΔGfº
(kJ/mol)
Sº (J/molK)
MgCl2 (s)
–642
–592
90
H2O (g)
–242
–229
189
MgO (s)
–602
–570
27
HCl (g)
–92
–95
187
Br2 (l)
0
0
152
Br2 (g)
30.7
3.14
245
22. [7 points] The hydrolysis of magnesium chloride occurs through the following
reaction:
MgCl2(s) + H2O(g) → MgO(s) + 2 HCl(g)
What is the value of ΔG0 for this reaction under standard conditions (pressure
= 1 atm, T = 298 K)?
a.
b.
c.
d.
e.
–61 kJ
+61 kJ
-1581 kJ
+156 kJ
-156 kJ
23. [7 points] What is the value of ΔG0 for the hydrolysis of magnesium chloride at
450 K (assume entropy and enthalpy do not change as a function of
temperature)?
a.
b.
c.
d.
e.
–174 kJ
+79 kJ
-54,800 kJ
+219 kJ
+43 kJ
24. [7 points] What value would you estimate for the boiling point of Br2 (where
the liquid and vapor are in equilibrium) if we assume entropy and enthalpy do
not change as a function of temperature?
a.
b.
c.
d.
e.
57 °C
–272 °C
125 °C
305 °C
None of the above
25. [7 points] Consider the reaction:
NH3 (g) + HCl (g) ↔ NH4Cl (s)
Given the following table of thermodynamic data at 298 K:
ΔHfº
(kJ/mol)
Sº (J/molK)
NH3 (g)
–46.19
192.5
HCl (g)
–92.30
186.69
NH4Cl (s)
–314.4
94.6
Compound
The value of the equilibrium constant Keq for the reaction at 25 °C is __________.
a.
b.
c.
d.
e.
Keq
Keq
Keq
Keq
Keq
= 150
= 9.3 × 1015
= 8.4 × 104
= 1.1 × 10–16
= 1.4 × 108
Useful Equations
ΔG = ΔH - TΔS
ΔGºrxn = ΣnΔGºf(products) - ΣmΔGºf(reactants)
ΔG = ΔGº + RT ln(Q)
Keq = exp[-ΔGº/RT]
Physical Constants
h = 6.626 × 10-34 J-s
c = 2.998 × 108 m/s
R = 8.314 J/K-mol
1 Å = 10 pm = 1 × 10-10 m
1 eV = 1.602 × 10-19 J
1 F = 96,500 C/mol = 96,500 J/V-mol
1 A = 1 C/s
1 eV = 1.602 × 10-19 J
Formation Constants for Some Metal Complex Ions in Water at 25°C