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CHEM 160-
Practice Final Exam (150 points)
Name _________________________ May 8, 2006
General Instructions
- The format of this exam is 75 multiple-choice questions, 2 points each. There is only one correct answer to each question. If you make a mistake, completely erase your mistake. If you fail to erase your first answer, you will not receive credit for the problem. NO partial question will be awarded, so there is no penalty for guessing.
- Useful constants:
1 amu = 1.66054 × 10 -27^ kg 1 atm = 760 Torr = 760 mm Hg Boltzmann constant (k) = 1.38065 × 10 -23^ J K- Gas constant (R) = 0.08205 L atm mole-1^ K- = 8.31447 J mole-1^ K- Avogadro’s number (Na) = 6.02214 × 1023 mole- Ion Product of Water (Kw) = 1.000 × 10 -14^ at 25.0 °C Faraday constant (F) = 96,485 C mole- RT/F = 0.0257 V at 25°C
- Assume a temperature of 298 K unless otherwise specified.
- A useful exam strategy is to look over the entire exam briefly when you receive it and to work the problems or questions that you know how to do first. Then go back and try the questions that you are not so certain you know how to work.
- A periodic table and table of standard reduction potentials are attached to the end of the exam for your reference.
- Some common ions and their charges are:
F-, fluoride S 2 O 3 2-, thiosulfate Cl-, chloride C 2 O 4 2-, oxalate Br-, bromide CN-, cyanide I-, iodide SCN-, thiocyanate NO 3 - , nitrate ClO 4 - , perchlorate NO 2 - , nitrite SO 3 2-, sulfite SO 4 2-, sulfate edta4-, ethylenediaminetetraacetate
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
- Which one of the following substances should exhibit hydrogen bonding in the liquid state?
A. PH 3 B. H 2 C. H 2 S D. CH 4 E. NH 3
- Which of the following substances should have the highest boiling point?
A. CH 4 B. Cl 2 C. Kr D. CH 3 Cl E. N 2
- Which of the following liquids would have the highest viscosity at 25ºC?
A. CH 3 OCH 3
B. CH 2 Cl (^2) C. C 2 H 5 OH D. CH 3 Br E. HOCH 2 CH 2 OH
- Which of the following properties indicates the presence of weak intermolecular forces in a liquid?
A. a high heat of vaporization B. a high critical temperature C. a high vapor pressure D. a high boiling point E. None of the above.
- The heat capacity for liquid water is 4.18 J/g• °C and the heat of vaporization ( ) is
40.7 kJ/mol. How many kilojoules (kJ) of heat must be provided to convert one gram of liquid water at 67°C into one gram of steam at 100°C?
o ∆ Hvap
A. 22.6 kJ B. 40.8 kJ C. 2.2 kJ D. 2,400 J E. 40.8 J
- Which of the following is NOT an endothermic process?
A. melting of a solid B. vaporization C. raising the temperature of a gas D. condensation of water vapor E. sublimation of dry ice
- The vapor pressure of ethanol is 400 mmHg at 63.5°C. Its molar heat of vaporization
( ∆ Hvapo ) is 39.3 kJ/mol. What is the vapor pressure of ethanol, in mmHg ,at 34.9°C?
A. 1,510 mmHg B. 100 mmHg C. 200 mmHg D. 0.0099 mmHg E. 4.61 mmHg
- The reaction
A + 2B → products
was found to follow the rate law: rate = k[A] 2 [B]. Predict by what factor the rate of reaction will increase when the concentration of A is doubled and the concentration of B is tripled, and the temperature remains constant.
A. 5
B. 6
C. 12
D. 18
E. None of the above.
- Nitric oxide reacts with hydrogen to form nitrous oxide, and water. Use the following data to determine the rate law for the reaction.
2NO + H 2 → N O 2 +H O 2
Expt. # [ NO]^0 [ H^2 ] 0 Initial rate
1 0.021 0.065 1.46 M/min 2 0.021 0.260 1.46 M/min 3 0.042 0.065 5.84 M/min
A. rate = k[NO] B. rate = k[NO] 2 C. rate = k[NO][H 2 ] D. rate = k[NO] 2 [H 2 ] E. rate = k[NO] 2 [H 2 ]^2
- A certain first-order reaction A → B is 25% complete in 42 min at 25°C. What is the half- life of the reaction?
A. 21 min B. 42 min C. 84 min D. 101 min E. 120 min
- A first-order reaction has a rate constant of 3.0 × 10 –3/s. The time required for the reaction to be 75% complete is:
A. 95.8 s B. 201 s C. 231 s D. 462 s E. 41.7 s
- The activation energy for the following reaction is 60 kJ/mol.
By what factor (how many times) will the rate constant increase when the temperature is raised from 10°C to 28°C?
2 3 4+
Sn 2Co Sn 2Co
2 +
A. 1.002 B. 4.6 C. 5.6 D. 2.8 E. 696
- 1.25 moles of NOCl were placed in a 2.50 L reaction chamber at 427°C. After equilibrium was reached, 1.10 moles of NOCl remained. Calculate the equilibrium constant, Kc, for the reaction:
2NOCl(g) ⇔ 2NO(g) +Cl (g) 2
A. 3.0 × 10 –4^ B. 1.8 × 10 3 C. 1.4 × 10 –3^ D. 5.6 × 10–4^ E. 4.1 × 10–
- Phosgene, COCl 2 , a poisonous gas, decomposes according to the equation:
COCl (g) 2 ⇔ CO(g) +Cl (g) 2
Calculate Kp for this reaction if Kc = 0.083 at 900°C.
A. 0.125 B. 8.0 C. 6.1 D. 0.16 E. 0.
- At 700 K, the reaction
has an equilibrium constant Kc = 4.3 × 106 , and the following concentrations are present:
[SO 2 ] = 0.10 M; [SO3 ] = 10 M; [O 2 ] = 0.10 M.
Is the mixture at equilibrium? If not at equilibrium, in which direction,
2SO (g) 2 + O (g) 2 ⇔2SO (g) 3
left to right, or right to left, will reaction occur to reach equilibrium?
A. yes, the mixture is at equilibrium. B. no, left to right C. no, right to left D. There is not enough information to tell.
- For the reaction
PCl (g) 3 + Cl (g) 2 ⇔ PCl (g) ; K 5 C=24.
a system is prepared with:
[PCl 3 ] = 0.10 M [Cl 2 ] = 0.15 M [PCl 5 ] = 0.60 M.
Which response is correct? The reaction
A. is at equilibrium. B. will form more PCl 5 until equilibrium is reached. C. will form PCl 3 and Cl 2 until equilibrium is reached. D. None of the above.
- For the following reaction at equilibrium
if we increase the reaction temperature, the equilibrium will
O
2SO (g) 3 ⇔ 2SO (g) 2 + O (g) ; 2 ∆H rxn=198 kJ
A. shift to the right. B. shift to the left. C. stay the same. D. The question cannot be answered because Keq is not given.
- A Brønsted-Lowry base is defined as a substance that __________.
A. tastes bitter B. increases [OH-] when placed in H 2 O C. acts as a proton donor D. acts as an electron pair donor E. acts as a proton acceptor
- A Lewis acid is defined as a substance that __________.
A. increases [H+] when placed in H 2 O B. tastes sour F. acts as an electron pair acceptor G. acts as an electron pair donor H. acts as a proton donor
- The OH–^ concentration in 7.5 × 10–3^ M Ca(OH) 2 is
A. 7.50 × 10–3^ M.
B. 1.50 × 10 –2^ M.
C. 1.30 × 10 –12^ M.
D. 1.00 × 10–7^ M.
E. 1.00 × 10 –14^ M.
- What is the H+^ ion concentration in a 4.8 × 10 –2^ M KOH solution?
A. 4.8 × 10 –2^ M
B. 1.0 × 10 –7^ M
C. 4.8 × 10 –11^ M
D. 4.8 × 10 –12^ M
E. 2.1 × 10 –13^ M
- The pH of a 0.55M aqueous solution of hypobromous acid ( a weak acid ), HBrO, at 25 °C is 4.48. What is the value of Ka for HBrO?
A. 6.0 × 10-
B. 3.0 × 10^4
C. 1.1 × 10-
D. 2.0 × 10-
E. 3.3 × 10-
- Consider a weak acid CH 3 COOH (acetic acid). Given that a 0.048 M CH 3 COOH solution is 5.2% ionized, determine the [H 3 O+] concentration at equilibrium.
A. 0.25 M
B. 9.2 × 10 –3^ M
C. 0.048 M
D. 0.052 M
E. 2.5 × 10–3^ M
- A 0.10 M NH 3 solution is 1.3% ionized. Calculate the H+^ ion concentration.
NH (aq) 3 H O(l) 2 NH (aq) 4 OH (aq)
+ ⇔ +^ + −
A. 1.3 × 10–3^ M
B. 7.7 × 10 –2^ M
C. 7.7 × 10 –14^ M
D. 0.13 M
E. 0.10 M
- Determine the pH of a KOH solution made from 0.251 g KOH and enough water to make 100.0 mL of solution.
A. 1.35 B. 2.35 C. 7.00 D. 11.65 E. 12.
- What is the pH of a solution prepared by mixing 10.0 mL of a strong acid solution with pH = 2.00 and 10.0 mL of a strong acid solution with pH = 6.00?
A. 2.0 B. 2.3 C. 4.0 D. 6.0 E. 8.
- Which solution will have the lowest pH?
A. 0.10 MHCN
B. 0.10 MHNO 3
C. 0.10 MNaCl D. 0.10 MH 2 CO 3 E. 0.10 MNaOH
- Which one of the following salts will form a neutral solution on dissolving in water?
A. NaCl B. KNO 2 C. NaCN D. NH 4 NO 3 E. FeCl (^3)
- Which one of the following salts will form a basic solution on dissolving in water?
A. NaCl B. KCN C. NaNO 3 D. NH 4 NO 3 E. FeCl (^3)
- What is the pH of a 0.20M solution of NH 4 Cl? Given Kb (NH 3 ) = 1.8 10–^.
A. 3.74 B. 4.98 C. 6.53 D. 9.02 E. 10.
- Which one of the following salts will form an acidic solution on dissolving in water?
A. LiBr B. NaF C. KOH D. FeCl 3 E. NaCN
- Which one of the following is a buffer solution?
A. 0.40 M HCN and 0.10 KCN B. 0.20 M CH 3 COOH C. 1.0 M HNO 3 and 1.0 MNaNO 3 D. 0.10 M KCN E. 0.50 M HCl and 0.10 NaCl
- Which of the following is the most acidic solution?
A. 0.10 M CH 3 COOH and 0.10 M CH 3 COONa B. 0.10 M CH 3 COOH C. 0.10 M HNO 2 D. 0.10 M HNO 2 and 0.10 M NaNO 2 E. 0.10 M CH 3 COONa
- Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C 6 H 5 CO 2 H) and
0.15 M sodium benzoate (C 6 H 5 COONa). Given Ka = 6.5 × 10 –5^ for benzoic acid.
A. 3.97 B. 4.83 C. 4.19 D. 3.40 E. 4.
- Consider a buffer solution prepared from HOCl and NaOCl. Which is the net ionic equation for the reaction that occurs when NaOH is added to this buffer?
A. OH–^ + HOCl → H 2 O + OCl – B. OH–^ + OCl –^ → HOCl + O2– C. Na +^ + HOCl → NaCl + OH– D. H+^ + HOCl → H 2 + OCl – E. NaOH + HOCl → H 2 O + NaCl
- Calculate the minimum concentration of Cr3+^ that must be added to 0.095 MNaF solution in order to initiate a precipitate of chromium (III) fluoride. For CrF 3 , Ksp = 6.6 × 10 –
.
A. 0.023 M B. 0.032 M C. 7.7 × 10–8^ M D. 2.9 × 10 –9^ M E. 6.9 × 10 –10^ M
- Silver chloride (AgCl(s)) will be most soluble in a solution of:
A. 0.10 M AgNO 3 B. distilled water C. 0.10 M NaCl D. 0.10 M HCl E. 0.10 M aqueous NH 3
- Which of the following species has the highest entropy (S°) at 25°C?
A. CH 3 OH(l) B. CO(g) C. MgCO 3 (s) D. H 2 O(l) E. Ni(s)
- Determine ∆S° for the following reaction.
Given the following absolute entropies;
SO (g) 3 + H O(l) 2 →H SO (l) 2 4
S°(J/K• mol) SO 3 256. H 2 O 69. H 2 SO 4 156.
A. ∆S° = 169.3 J/K
B. ∆S° = 1343.2 J/K
C. ∆S° = -169.3 J/K
D. ∆S° = -29.4 J/K
E. ∆S° = 29.4 J/K
- The entropy change on vaporization (∆Svap ) of a compound or element is
A. always negative. B. always positive. C. sometimes is positive and sometimes is negative. D. usually zero.
- A negative sign for ∆G indicates that, at constant T and P,
A. the reaction is exothermic. B. the reaction is endothermic. C. the reaction is fast. D. the reaction is spontaneous. E. ∆S must be > 0.
- Hydrogen peroxide (H 2 O 2 ) decomposes according to the equation:
2 2 2 2
H O (l) H O(l) O (g)
From the following data calculate Kp for this reaction at 25°C.
∆H° = –98.2 kJ ∆S° = 70.1 J/K
A. 1.3 × 10 –
B. 20.
C. 3.46 × 1017
D. 7.7 × 1020
E. 8.6 × 104
- The equilibrium constant for the reaction:
AgBr(s) Ag (aq) Br (aq)
is the solubility product constant, Ksp = 7.7 × 10–13^ at 25°C. Calculate ∆G for the reaction when [Ag+^ ] = 1.0 × 10–2^ M and [Br–] = 1.0 × 10–3^ M. Is the reaction spontaneous or nonspontaneous at these concentrations?
A. ∆G = 69.1 kJ, nonspontaneous B. ∆G = -69.1 kJ, spontaneous C. ∆G = 97.5 kJ, spontaneous D. ∆G = 40.6 kJ, nonspontaneous E. ∆G = -97.5 kJ, nonspontaneous
- A certain electrochemical cell has for its cell reaction:
Which is the half-reaction occurring at the anode?
Zn(s) + HgO(s) ⇔ ZnO(s) +Hg(l)
A.
Hg2+ + 2 e −→Hg(l)
B.
2+
Zn 2 e Zn(s)
−
C.
2+
Zn(s) Zn 2 e
−
D.
Hg(l) → Hg 2++ 2 e −
- Calculate the value of E°cell for the following reaction:
2Au(s) + 3Ca 2 +(aq) → 2Au3+ (aq) +3Ca(s)
A. -4.37 V B. -1.37 V C. -11.6 V D. 1.37 V E. 4.37 V
- Which of the following reactions will occur spontaneously?
A.
2+ 2+
Mg (aq) + Ca(s) → Mg(s) +Ca (aq)
B.
3+
Au(s) 3K (aq) Au (aq) 3K(s)
C.
2Al 3+^ (aq) + 3Fe(s) → 2Al(s) +3Fe 2 +(aq)
D.
2+
Cu(s) 2H (aq) Cu (aq) H (g) 2
- Which of the following reagents is the strongest reducing agent?
A. Cr 3+^ B. Cr C. Mn2+^ D. Co E. MnO 4 –
