Chemistry 1304.001
Exam 3 (100 points)
Name (please print)
March 22, 2017
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
1.
Date
The pH of a certain brand of orange juice is approximately 4.0. The [H+] is
times greater in this orange juice than in neutral water?
(2 points)
2. (2 points) The pH of a 0.10 M solution of HF is
.
3. (2 points) The pH of pure water at 10 °C is 7.27 so the Kw of water at 10 °C is
4. (2 points) The conjugate acid of PF4– is
5. (4 points) The pH of 0.10 M H2CO3 is
and
the
a
strong
concentration
of
CO32-
ions
is
.
6. (2 points)
Smelling
salt,
(NH4)2CO3
produces
odor
ions to produce gaseous
because of conversion of
.
7. (6 points) Write BOTH the equilibrium reaction (including states) and the properly labeled
equilibrium constant expression (Ka, Kb, Kc, KP, Kw etc.) for aqueous solution of the following.
Mg(HCOO)2
a mixture of NH4NO3 and NH3
8. (9 points) Indicate whether an aqueous solution of each of the following substances is acidic (A), basic
(B), neutral (N), or amphoteric (Amp).
RbNO3
HCOOH
BaO
CO2
CrBr3
Al2O3
K3PO4
Zn(OH)2
NaNO2
9. (4 points) Indicate whether an aqueous solution of each of the following substances is acidic (A), basic
(B), or neutral (N).
[NH4][CH3COO]
[C5H5NH]F
10. (2 points) Among the following, underline the weakest Brønsted-Lowry acid.
H3PO4
H2SO4
H3AsO3
H3PO3
H2SO3
H3AsO4
11. (6 points) Consider the following reaction in terms of the Lewis Acid-Base concept. Write complete
Lewis electron dot formulas for all reactants and products. Clearly indicate which reactant is the
Lewis acid and which is the Lewis base. Use arrows to illustrate the formation and breaking of any
bonds as the reaction proceeds from left to right. {Hint: The location of a multiple bond in BrCN is
shown, but you need to add the remaining electrons.]
PBr3
+
Br–C≡N →
PBr4+
+ CN
12. (10 points)
a.
10
The plot on the right is the titration of
50.0 mL of a weak
strong
with a
8
with a molarity of 0.30
M.
6
b. Circle the buffer region on the plot.
c. The concentration of the weak component is
4
and its pKa is
. SHOW all WORK.
2
0
0
10
20
30
40
mL of titrating solution
13. (6 points) A 0.80 M solution of a monoprotic acid is 12 percent ionized.
constant, Ka, for the acid.
50
Calculate the ionization
60
14. (8 points) Calculate the pH of the solution formed by mixing 20.0 mL of a 0.47 M HF with 15.0 mL of a
0.20 M KF solution.
2. SHOW ALL WORK. A 0.212-gram sample of an unknown organic base (i.e., RNH2) is dissolved in
enough water to make 50.0 mL of solution. This solution is then titrated with 0.1144 M HCl and
31.20 mL of the HCl solution is required to reach the equivalence point. The pH of the solution at
the equivalence point is found to be 6.03.
a.
(6 points)
Determine the molecular mass of the unknown base, RNH2.
b. (10 points) Determine the pKb value of the unknown base, RNH2. Include a balanced chemical
equation for the equilibrium reaction that is occurring in the solution at the equivalence point.
15. a.
SHOW ALL WORK. As the TA for a Gen Biology lab, you are required to prepare a
buffer solution with a pH of 6.38. The only instructions you are given is to start with 10.0 L of
3.0 M NaHCO3 that another TA already made. You look around the lab and find are a 2.0 L
(9 points)
bottles of concentrated HCl (11.65 M) and 1000 g bottle of solid NaOH (molar mass 40.0 g).
CAREFULLY and CLEARLY show your calculations and describe how you would convert the 10.0 L
of 3.0 M NaHCO3 to a buffer with pH 6.38.
c.
(10 points)
Unfortunately, your biology professor decides that pH of 6.38 is not quite what was
needed since the experiment involved blood plasma where the pH should be 7.40. She tells you
to change the pH the 10.0 L of buffer solution that you already made to pH 7.40. Describe
what you would do and CLEARLY SHOW ALL CALCULATIONS fully demonstrating that the pH
of the new solution is 7.40.
Bonus: (3 points)
Derive the Henderson-Hasselbach (HaHaHaHa) equation.
You must show at least
FOUR logical algebraic steps CLEARLY. If you USED this equation anywhere on this exam, you
must do this derivation to received HALF credit where you used it and ONLY IF you used it
correctly.
Ionization Constants (Ka) for some ACIDS
Ionization Constants (Kb) for some BASES
CH3COOH
1.8 × 10-5
NH3
1.8 × 10-5
HNO2
4.5 × 10-4
CH3NH2
4.4 × 10-4
HCOOH
1.7 × 10-4
C5N5HN
1.7 × 10-9
HF
7.1 × 10-4
C6H5NH2
3.8 × 10-10
H3BO3
5.4 × 10-10
HCN
4.9 × 10-10
H2CO3
Ka1 = 4.2 × 10-7, Ka2 = 4.8 × 10-11
Chemistry 1304.001
Exam 3 (100 points)
Name (please print)
March 22, 2017
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
1.
Date
The pH of a certain brand of orange juice is approximately 4.0. The [H+] is
times greater in this orange juice than in neutral water?
(2 points)
2. (2 points) The pH of a 0.10 M solution of HF is
.
3. (2 points) The pH of pure water at 10 °C is 7.27 so the Kw of water at 10 °C is
4. (2 points) The conjugate acid of PF4– is
5. (4 points) The pH of 0.10 M H2CO3 is
and
the
a
strong
concentration
of
CO32-
ions
is
.
6. (2 points)
Smelling
salt,
(NH4)2CO3
produces
odor
ions to produce gaseous
because of conversion of
.
7. (6 points) Write BOTH the equilibrium reaction (including states) and the properly labeled
equilibrium constant expression (Ka, Kb, Kc, KP, Kw etc.) for aqueous solution of the following.
Mg(HCOO)2
a mixture of NH4NO3 and NH3
8. (9 points) Indicate whether an aqueous solution of each of the following substances is acidic (A), basic
(B), neutral (N), or amphoteric (Amp).
RbNO3
HCOOH
BaO
CO2
CrBr3
Al2O3
K3PO4
Zn(OH)2
NaNO2
9. (4 points) Indicate whether an aqueous solution of each of the following substances is acidic (A), basic
(B), or neutral (N).
[NH4][CH3COO]
[C5H5NH]F
10. (2 points) Among the following, underline the weakest Brønsted-Lowry acid.
H3PO4
H2SO4
H3AsO3
H3PO3
H2SO3
H3AsO4
11. (6 points) Consider the following reaction in terms of the Lewis Acid-Base concept. Write complete
Lewis electron dot formulas for all reactants and products. Clearly indicate which reactant is the
Lewis acid and which is the Lewis base. Use arrows to illustrate the formation and breaking of any
bonds as the reaction proceeds from left to right. {Hint: The location of a multiple bond in BrCN is
shown, but you need to add the remaining electrons.]
PBr3
+
Br–C≡N →
PBr4+
+ CN
12. (8 points)
a.
10
The plot on the right is the titration of a
weak
with a strong
8
with a molarity of 0.30 M.
b. Circle the buffer region on the plot.
6
c. The concentration of the weak component is
and its pKa is
4
. SHOW all WORK.
2
0
0
10
20
30
40
mL of titrating solution
13. (6 points) A 0.80 M solution of a monoprotic acid is 12 percent ionized.
constant, Ka, for the acid.
50
Calculate the ionization
60
14. (8 points) Calculate the pH of the solution formed by mixing 20.0 mL of a 0.47 M HF with 15.0 mL of a
0.20 M KOH solution.
2. SHOW ALL WORK. A 0.212-gram sample of an unknown organic base (i.e., RNH2) is dissolved in
enough water to make 50.0 mL of solution. This solution is then titrated with 0.1144 M HCl and
31.20 mL of the HCl solution is required to reach the equivalence point. The pH of the solution at
the equivalence point is found to be 6.03.
a.
(6 points)
Determine the molecular mass of the unknown base, RNH2.
b. (10 points) Determine the pKb value of the unknown base, RNH2. Include a balanced chemical
equation for the equilibrium reaction that is occurring in the solution at the equivalence point.
15. a.
SHOW ALL WORK. As the TA for a Gen Biology lab, you are required to prepare a
buffer solution with a pH of 6.38. The only instructions you are given is to start with 10.0 L of
3.0 M NaHCO3 that another TA already made. You look around the lab and find are a 2.0 L
(9 points)
bottles of concentrated HCl (11.65 M) and 1000 g bottle of solid NaOH (molar mass 40.0 g).
CAREFULLY and CLEARLY show your calculations and describe how you would convert the 10.0 L
of 3.0 M NaHCO3 to a buffer with pH 6.38.
c.
(10 points)
Unfortunately, your biology professor decides that pH of 6.38 is not quite what was
needed since the experiment involved blood plasma where the pH should be 7.40. She tells you
to change the pH the 10.0 L of buffer solution that you already made to pH 7.40. Describe
what you would do and CLEARLY SHOW ALL CALCULATIONS fully demonstrating that the pH
of the new solution is 7.40.
Bonus: (3 points)
Derive the Henderson-Hasselbach (HaHaHaHa) equation.
You must show at least
FOUR logical algebraic steps CLEARLY. If you USED this equation anywhere on this exam, you
must do this derivation to received HALF credit where you used it and ONLY IF you used it
correctly.
Ionization Constants (Ka) for some ACIDS
Ionization Constants (Kb) for some BASES
CH3COOH
1.8 × 10-5
NH3
1.8 × 10-5
HNO2
4.5 × 10-4
CH3NH2
4.4 × 10-4
HCOOH
1.7 × 10-4
C5N5HN
1.7 × 10-9
HF
7.1 × 10-4
C6H5NH2
3.8 × 10-10
H3BO3
5.4 × 10-10
HCN
4.9 × 10-10
H2CO3
Ka1 = 4.2 × 10-7, Ka2 = 4.8 × 10-11