Chemistry 112
Practice Exam 2C
Name
Section
_______________________
_______________________
eMail
_______________________
IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student
number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a
#2 pencil.
There are 25 questions on this exam. Check that you have done all of the problems and filled in the first
25 bubbles on the scantron BEFORE TIME IS CALLED. The maximum score on this exam is 25 points.
Your score will be reported in percent (max 100%).
Exam policy
●
●
●
●
●
●
●
Hints
●
Calculators with text-programmable memory are not allowed.
Relevant data and formulas, including the periodic table, are attached at the end of this exam.
Your grade will be based only on what is on the scantron form.
The answer key will be posted on ANGEL after the exam.
You have 75 minutes to complete this exam.
You must completely fill in your scantron bubbles before the 75 minute period has ended.
You must turn in your cover sheet with your scantron answer form.
As you read the question, underline or circle key words to highlight them for yourself. Avoid
errors from "mis-reading" the question.
●
Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations.
●
There is no penalty for guessing.
●
Circle the answer you choose so that you can grade yourself using the answer key posted after the
exam.
Chem 112 Practice Exam 2C
Thermodynamics, Acid/Base Chemistry
---------------------------------------------------------------------------------------------------------------------------1. The lab of Rick T. Cat has discovered a new element and has named it Nittnium, with a symbol of Nt!
Nittnium oxide, Nt2O3, forms a basic solution at 25°C. Based on this information, what type of element
is Nittnium?
A.
B.
C.
D.
E.
Metal
Non-metal
Metalloid
Halogen
Noble gas
---------------------------------------------------------------------------------------------------------------------------2. Which one of the following species will have a negligible effect on the pH of a solution?
A.
B.
C.
D.
E.
BrO¯
Cl¯
+
NH4
2
CO3 ¯
CH3COO¯
---------------------------------------------------------------------------------------------------------------------------3. What are the conjugate base and conjugate acid of the ascorbate ion, C6H7O6¯?
Conjugate
base
Conjugate
acid
A.
C 6H 6O 6 ¯
2
C 6H 8O 6
B.
C 6H 8O 6
C 6H 7O 6¯
C.
C 6H 7O 6¯
C 6H 8O 6
D.
C 6H 8O 6
C 6H 6O 6 ¯
E.
C 6H 6O 6 ¯
2
C 6H 5O 6 ¯
2
3
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------4. Which statement is TRUE?
A. The melting of a substance at its melting point is an isothermal process (T is constant).
B. The quantity of energy gained by a system equals the quantity of energy gained by its surroundings.
C. The entropy of a pure crystalline substance at 25°C is zero.
D. The more negative ΔG° is for a given reaction, the smaller the value of the corresponding equilibrium
constant, K.
E. Thermodynamics studies the speed at which a reaction takes place.
---------------------------------------------------------------------------------------------------------------------------5. Rank the following carboxylic acids in order of acidity from least acidic to most acidic when in an
aqueous solution at 25°C:
A.
B.
C.
D.
E.
i < ii < iii < iv
ii < iii < iv < i
i < iv < iii < ii
iv < i < iii < ii
i < iii < ii < iv
--------------------------------------------------------------------------------------------------------------------------6. Which one of the following reactions has ΔS > 0?
A. CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)
B. 2 Na (s) + Cl2 (g) → 2 NaCl (s)
C. MgSO4 (aq) + Ca(NO3)2 (aq) → CaSO4 (s) + Mg(NO3)2 (aq)
D. 2 H2 (g) + O2 (g) → 2 H2O (l)
E. 2 Cs(s) + 2 H2O(l) → 2 CsOH (aq) + H2 (g)
----------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Consider the following reaction for the next TWO questions:
Zn
2+
(aq) + 4 NH3 (aq) → [Zn(NH3)4]
2+
(aq)
7. Which species is acting as a Lewis acid in this reaction?
2+
A. Zn (aq)
B. NH3 (aq)
2+
C. [Zn(NH3)4] (aq)
2+
D. (NH3)4 (aq)
+
E. NH4 (aq)
--------------------------------------------------------------------8. Using the data in the table below, what is ∆Go at 25°C for the reaction above?
∆H°f (kJ/mol)
S° (J/mol-K)
(aq)
̶ 152.4
̶ 106.5
NH3 (aq)
̶ 80.3
111.3
̶ 533.5
301.0
Zn
2+
[Zn(NH3)4]
A.
B.
C.
D.
E.
2+
(aq)
̶ 59.9 kJ/mol
4
+1.1 x 10 kJ/mol
+72.6 kJ/mol
̶ 48.7 kJ/mol
0 kJ/mol
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------9. What is ΔG° for the auto-ionization of water at 25°C?
A.
B.
C.
D.
E.
+79.9 kJ/mol
+6.7 kJ/mol
̶ 6.5 kJ/mol
̶ 54.8 kJ/mol
0 kJ/mol
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------10. Citric acid (C6H8O7) is a polyprotic acid found in fruits that can successively lose three carboxylic
acid protons; its structure is shown below. Which one of the following statements is TRUE at 25°C?
4
Ka1 = 7.41 x 10¯
5
Ka2 = 1.74 x 10¯
7
Ka3 = 4.07 x 10¯
A.
B.
C.
D.
E.
C6H7O7¯ is a stronger acid than C6H8O7.
The overall pH of a citric acid solution is determined by the third proton dissociation and Ka3.
3
2
C6H5O7 ¯ is a stronger base than both C6H7O7¯ and C6H6O7 ¯ .
2
C6H8O7 and C6H6O7 ¯ can both be considered amphoteric species.
3
[C6H5O7 ¯ ] = [C6H8O7]initial at equilibrium.
---------------------------------------------------------------------------------------------------------------------------11. Benzimidazole is an important organic base that comprises an important portion of vitamin B12. Its
structure is shown below. What is the pH of a 1.5 M aqueous solution of benzimidazole at 25°C if Kb =
9
3.98 x 10¯ ?
A.
B.
C.
D.
E.
8.22
4.11
5.78
10.33
9.89
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------12. Calculate ΔS°rxn for the following reaction, given the values in the table.
NH3 (g) + HCl(g) → NH4Cl(s)
Molecule
S° (J mol¯1 K¯1)
H2 (g)
130.59
HCl (g)
186.77
Cl2 (g)
222.97
N2 (g)
191.50
NH3 (g)
192.34
NH4Cl(g)
94.56
A. ̶ 545 J mol¯1 K¯1
B. ̶ 285 J mol¯1 K¯1
C. ̶ 72 J mol¯1 K¯1
D. 6 J mol¯1 K¯1
E. 128 J mol¯1 K¯1
---------------------------------------------------------------------------------------------------------------------------13. What is the the change in enthalpy associated with the vaporization of ethanol at 78.4°C when S° of
C2H5OH (ℓ) = 161.04 J/mol-K and S° of C2H5OH (g) = 282.59 J/mol-K?
A.
B.
C.
D.
E.
121.55 kJ/mol
42.71 kJ/mol
9.53 kJ/mol
4
3.62 x 10 kJ/mol
0 kJ/mol
---------------------------------------------------------------------------------------------------------------------------14. Which of the following substances has the highest absolute entropy at 75°C?
A. H2 (g)
B. CH4 (g)
C. C2H6 (g)
D. C4H10 (g)
E. C5H12 (g)
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------15. Which of the following solutions has a pH < 7 at 25°C?
i. NH4Cl (aq)
ii. CaO (aq)
iii. NaNO2 (aq)
iv. KClO4 (aq)
v. CH3COOH (aq)
A. i and ii only
B. ii and iv only
C. i, iii, and v only
D. ii, iv, and v only
E. i and v only
---------------------------------------------------------------------------------------------------------------------------16. Ibuprofen is the active ingredient of the over-the-counter painkiller Advil. Its structure is shown
below. Like other non-steroidal anti-inflammatory drugs, it works by inhibiting the synthesis of
prostaglandins involved in the inflammation, pain, and fever pathway of the body. What is the Ka of
ibuprofen if a 0.55 M aqueous solution of ibuprofen has a pH of 2.58 at 25°C?
A.
B.
C.
D.
E.
3
1.45 x 10¯
5
1.26 x 10¯
7
7.31 x 10¯
8
4.59 x 10¯
3
2.63 x 10¯
---------------------------------------------------------------------------------------------------------------------------17. Please rank the following 1M salts in order of increasing pH at 25°C:
NaCl, NH4Cl, NaBrO3, NaBrO
Lowest pH
Highest pH
A. NaBrO < NaBrO3 < NH4Cl < NaCl
B. NH4Cl < NaCl < NaBrO3 < NaBrO
C. NaCl < NaBrO3 < NaBrO < NH4Cl
D. NH4Cl < NaCl < NaBrO < NaBrO3
E. NaCl < NH4Cl < NaBrO3 < NaBrO
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------18. Which one of the following reactions is BEST described by the graph below?
A. C6H12O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (g)
B. 2 C8H18 (ℓ) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (g)
C. Heat + CaCO3 (s) → CaO (s) + CO2 (g)
D. 2 H2 (g) + O2 (g) → 2 H2O (g)
E. Heat + 3 O2 (g) → 2 O3 (g)
---------------------------------------------------------------------------------------------------------------------------19. Which one of the following solutions will have the highest pH at 25°C?
A. 1 M NaClO2 (aq)
B. 1 M NaClO4 (aq)
C. 1 M NaBrO2 (aq)
D. 1 M NaBrO4 (aq)
E. 1 M NaCl (aq)
---------------------------------------------------------------------------------------------------------------------------20. Palmitic acid, C15H31COOH, is an interesting molecule. It is the first fatty acid created in the
biochemical process where excess carbohydrates are converted into fat, and, accordingly, makes up about
5
one quarter of the fatty acids inside the human body. It also has a Ka = 1.66 x 10¯ at 25°C. What is the
pH of a 0.050 M solution of C15H31COOH at 25°C?
structure of palmitic acid
A.
B.
C.
D.
E.
4.7
8.2
1.3
3.0
2.5
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------21. Which of the following statements regarding thermodynamics is / are true?
i. At equilibrium, Q = Keq
ii. If ΔG < 0, then Q < Keq
iii. At equilibrium, ΔG° = 0
iv. If Q > Keq, then ΔG < 0
A. i and iii only
B. i and ii only
C. i and iv only
D. i, ii, and iii only
E. i, iii, and iv only
---------------------------------------------------------------------------------------------------------------------------22. Sodium cyanide (NaCN) is a potent inhibitor of respiration, making it one of the most rapidly acting
of all known poisons. Despite this, solutions of sodium cyanide are commonly used to extract gold from
low-grade ore in the mining industry. What is the pH of a 1.5 M solution of sodium cyanide at 25°C?
10
Ka of HCN = 6.2 x 10¯
A.
B.
C.
D.
E.
4.52
9.48
2.31
11.69
8.77
---------------------------------------------------------------------------------------------------------------------------23. Given the following thermodynamic data, what is the Keq of the Haber Process at 25°C?
Haber Process: N2 (g) + 3 H2 (g) ⇄ 2 NH3 (aq)
Molecule
ΔGOf
N2 (g)
0
H2 (g)
0
NH3 (g)
–16.48 kJ/mol
A. 1.6 x 10¯6
B. 33
C. 5.4 x 1017
D. 458
E. 6.0 x 105
----------------------------------------------------------------------------------------------------------------------------
24. Based on the free energy diagram depicted below for an important reaction at 25°C, which of the
following statements are TRUE?
i. Point e represents equilibrium.
ii. For this reaction, Keq > 1.
iii. At point d, Q > Keq.
iv. Arrow b represents ∆Grxn at point e.
v. At point a, the reaction is spontaneous in the forward direction.
A. i and v only
B. i, iii, and v only
C. iii and v only
D. ii, iii, and iv only
E. i, ii, iv, and v only
---------------------------------------------------------------------------------------------------------------------------25. What is the pOH of a 0.025 M solution of Ba(OH)2 at 25°C?
A.
B.
C.
D.
E.
1.6
12.4
1.3
12.7
7.0
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------END OF EXAM
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
ANSWER KEY
1. A
2. B
3. A
4. A
5. C
6. E
7. A
8. D
9. A
10. C
11. E
12. B
13. B
14. E
15. E
16. B
17. B
18. D
19. C
20. D
21. B
22. D
23. E
24. C
25. C