1082-2nd Chem Exam(A)-1090513
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Which one of the following is a Br∅nsted-Lowry base?
A) CH3COOH B) (CH3)3N C) HNO2 D) HF
E) none of the above Answer: B
2) Which one of the following statements regarding Kw is false?
A) Kw is known as the ion product of water.
B) pKw is 14.00 at 25 °C.
C) The value of Kw is always 1.0 × 10-14.
D) Kw changes with temperature.
E) The value of Kw shows that water is a weak acid.
Answer: C
3) The hydride ion, H-, is a stronger base than the hydroxide ion, OH-. The product(s) of the reaction of hydride ion with water is/are ________.
A) OH- (aq) + 2H+ (aq) B) H3O+ (aq)
C) no reaction occurs D) H2O2 (aq)
E) OH- (aq) + H2 (g) Answer: E
4) In the gas phase reaction below, NH3 is acting as a(n) ________.
A) Br∅nsted-Lowry acid B) Arrhenius acid C) Lewis base D) Lewis acid
E) Br∅nsted-Lowry base Answer: C
5) Of the acids in the table below, ________ is the strongest acid.
Acid Ka
HOAc 1.8 × 10-5 HCHO2 1.8 × 10-4 HClO 3.0 × 10-8 HF 6.8 × 10-4
A) HClO B) HCHO2 C) HF D) HOAc
E) HOAc and HCHO2 Answer: C
6) A substance that is capable of acting as both an acid and as a base is ________.
A) miscible B) conjugated C) autosomal D) amphiprotic E) saturated Answer: D
7) The Ka of hypochlorous acid (HClO) is 3.0 × 10-8 at 25.0 °C. What is the percent ionization of hypochlorous acid in a 0.015 M aqueous solution of HClO at 25.0 °C?
A) 4.5 × 10-8 B) 0.14 C) 2.1 × 10-5 D) 14 E) 1.4 × 10-3
Answer: B
8) Which of the following aqueous solutions has the highest [OH-]?
A) pure water
B) a 1 × 10-4 M solution of HNO3 C) a solution with a pOH of 12.0 D) a 1 × 10-3 M solution of NH4Cl
E) a solution with a pH of 3.0 Answer: A
9) A 0.5 M solution of ________ has a pH of 7.0.
A) NaF B) K2S C) KNO3 D) KF E) NH4Br
Answer: C
10) What is the pH of a 0.40 M aqueous solution of NH4Br at 25.0 °C? Kb for NH3 is 1.8 × 10-5.
A) 9.18 B) 2.57 C) 11.43 D) 11.23 E) 4.82
Answer: E
11) Of the compounds below, a 0.1 M aqueous solution of ________ will have the highest pH.
A) NaHS, Kb of HS- = 1.8 × 10-7 B) NaClO, Ka of HClO = 3.2 × 10-8 C) NaOAc, Ka of HOAc = 1.8 × 10-5 D) NH4NO3, Kb of NH3 = 1.8 × 10-5
12) A- is a weak base. Which equilibrium corresponds to the equilibrium constant Ka for HA?
A) A-(aq) + OH-(aq) ⇌ HOA2-(aq) B) A-(aq) + H3O+(aq) ⇌ HA(aq) + H2O(l) C) HA(aq) + H2O(l) ⇌ H2A+(aq) + OH-(aq) D) HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
E) A-(aq) + H2O(l) ⇌ HA(aq) + OH-(aq) Answer: D
13) The pH of an aqueous solution at 25.0 °C is 10.55. What is the molarity of H+ in this solution?
A) 3.45 B) 2.8 × 10-11 C) 1.1 × 10-13 D) 3.5 × 1010 E) 3.5 × 10-4 Answer: B
14) A 1.0 × 10-2 M aqueous solution of Ca(OH)2 at 25.0 °C has a pH of ________.
A) 2.0 × 10-2 B) 1.70 C) 12.00 D) 5.0 × 10-13 E) 12.30
Answer: E
15) Which one of the following pairs cannot be mixed together to form a buffer solution?
A) KOH, HF B) NH3, NH4Cl C) RbOH, HBr
D) NaC2H3O2, HCl (C2H3O2- = acetate) E) H3PO4, KH2PO4
Answer: C
16) The Henderson-Hasselbalch equation is ________.
A) [H+] = Ka + [base]
[acid]
B) pH = log [acid]
[base]
C) pH = pKa - log [base]
[acid]
D) pH = pKa + log [acid]
[base]
E) pH = pKa + log [base]
[acid]
Answer: E
17) The addition of KOH and ________ to water produces a buffer solution.
A) KF B) NH3 C) LiC2H3O2 D) HI
E) none of the above Answer: E
18) A result of the common-ion effect is ________.
A) that common ions precipitate all counter-ions
B) that some ions, such as Na+ (aq), frequently appear in solutions but do not participate in solubility equilibria
C) that ions such as K+ and Na+ are common ions, so that their values in equilibrium constant expressions are always 1.00
D) that the selective precipitation of a metal ion, such as Ag+, is promoted by the addition of an appropriate counterion (X-) that produces a compound (AgX) with a very low solubility E) that common ions, such as Na+ (aq), don't affect equilibrium constants
Answer: D
19) A 25.0 mL sample of a solution of an unknown compound is titrated with a 0.115 M NaOH solution. The titration curve above was obtained. The unknown compound is ________.
A) a strong acid B) a strong base C) a weak base D) a weak acid
E) neither an acid nor a base Answer: D
Indicator pKa
methyl orange 3.46
methyl red 5.00
bromocresol purple 6.12 bromthymol blue 7.10
thymol blue 8.90
phenolpthalein 9.10
20) A 25.0 mL sample of a solution of a monoprotic acid is titrated with a 0.115 M NaOH solution. The titration curve above was obtained. Which of the following indicators would be best for this titration?
A) thymol blue B) bromthymol blue C) methyl red D) phenolpthalein
E) bromocresol purple Answer: B
Consider the following table of Ksp values.
Name Formula Ksp
Cadmium carbonate CdCO3 5.2 × 10-12 Cadmium hydroxide Cd(OH)2 2.5 × 10-14 Calcium fluoride CaF2 3.9 × 10-11 Silver iodide AgI 8.3 × 10-17 Zinc carbonate ZnCO3 1.4 × 10-11
21) Which compound listed below has the greatest molar solubility in water?
A) CaF2 B) AgI C) ZnCO3 D) Cd(OH)2 E) CdCO3
Answer: A
22) In which one of the following solutions is silver chloride the most soluble?
A) pure H2O B) 0.750 M LiNO3 C) 0.0150 M NH3 D) 0.200 M HCl
E) 0.185 M KCl Answer: C
23) Which one of the following is not amphoteric?
A) Cr(OH)3 B) Ca(OH)2 C) Sn(OH)2 D) Al(OH)3 E) Zn(OH)2
Answer: B
24) The Ka of benzoic acid is 6.30 × 10-5. The pH of a buffer prepared by combining 50.0 mL of 1.00 M potassium benzoate and 50.0 mL of 1.00 M benzoic acid is ________.
A) 4.201 B) 1.705 C) 2.383 D) 0.851 E) 3.406
Answer: A
25) The concentration of fluoride ions in a saturated solution of barium fluoride is ________ M. The solubility product constant of BaF2 is 1.7 × 10-6.
A) 3.0 × 10-3 B) 1.5 × 10-2 C) 7.5 × 10-3 D) 1.4 × 10-4 E) 3.8 × 10-4 Answer: B
26) Calculate the maximum concentration (in M) of silver ions (Ag+) in a solution that contains 0.025 M of CO32-. The Ksp of Ag2CO3 is 8.1 × 10-12.
A) 1.8 × 10-5 B) 8.1 × 10-12 C) 2.8 × 10-6 D) 3.2 × 10-10 E) 1.4 × 10-6 Answer: A
27) Calculate the percent ionization of formic acid (HCO2H) in a solution that is 0.322 M in formic acid and 0.178 M in sodium formate (NaHCO2). The Ka of formic acid is 1.77 × 10-4.
A) 35.6 B) 0.1011 C) 1.03 × 10-3 D) 3.488 E) 10.8
Answer: B
28) Consider a solution containing 0.100 M fluoride ions and 0.126 M hydrogen fluoride. The concentration of fluoride ions after the addition of 9.00 mL of 0.0100 M HCl to 25.0 mL of this solution is ________ M. (HF Ka = 6.8 × 10-4 )
A) 0.00253 B) 0.0980 C) 0.0709 D) 0.0735 E) 0.0762
Answer: C
29) The first law of thermodynamics can be given as ________.
A) ΔS = qrev/T at constant temperature
B) ΔH°rxn = nΔH°f (products)
∑
- mΔH°f (reactants)∑
C) ΔE = q + w
D) the entropy of a pure crystalline substance at absolute zero is zero E) for any spontaneous process, the entropy of the universe increases Answer: C
30) A reversible process is one that ________.
A) must be carried out at low temperature B) happens spontaneously
C) is spontaneous in both directions D) must be carried out at high temperature
E) can be reversed with no net change in either system or surroundings Answer: E
31) Which one of the following correctly indicates the relationship between the entropy of a system and the number of different arrangements, W, in the system?
A) S = kW B) S = k lnW C) S = kW D) S = Wk E) S = Wk
Answer: B
32) Consider the reaction:
NH3 (g) + HCl (g) → NH4Cl (s)
Given the following table of thermodynamic data, Substance ΔHf° (kJ/mol) S° (J/mol ∙ K)
NH3 (g) -46.19 192.5
HCl (g) -92.30 186.69
NH4Cl (s) -314.4 94.6
determine the temperature (in °C) above which the reaction is nonspontaneous.
A) This reaction is spontaneous at all temperatures.
B) 618.1 C) 1235 D) 432.8
E) 345.0 Answer: E
33) ΔS is positive for the reaction ________.
A) 2 KClO3 (s) → 2KCl (s) + 3 O2 (g) B) 2 Ca (s) + O2 (g) → 2 CaO (s) C) HCl (g) + NH3 (g) → NH4Cl (s) D) CO2 (g) → CO2 (s)
E) Pb2+ (aq) + 2Cl- (aq) → PbCl2 (s) Answer: A
34) For an isothermal process, the entropy change of the surroundings is given by the equation:
A) ΔS = -q lnT B) ΔS = qsys T C) ΔS = q lnT D) ΔS = -qsys T
E) ΔS = -qsys / T Answer: E
35) For the reaction
2 C4H10 (g) + 13 O2 (g) → 8 CO2 (g) + 10 H2O (g)
ΔH° is -125 kJ/mol and ΔS° is +253 J/K ∙ mol. This reaction is ________.
A) spontaneous at all temperatures B) spontaneous only at high temperature C) spontaneous only at low temperature D) nonspontaneous at all temperatures
E) unable to determine without more information Answer: A
36) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for the reaction: ( R = 8.314 J/mol∙ K )
2SO2(g) + O2 (g) ⇌ 2 SO3 (g) Substance ΔHf° (kJ/mol) S° (J/mol ∙ K)
SO2 (g) -297 249
O2 (g) 0 205
SO3 (g) -395 256
A) 2.40 × 1024 B) 3.82 × 1023 C) 1.06 D) 1.95
E) More data are needed.
Answer: A
37) What is the equilibrium constant for a reaction at 25 °C. The value of ΔG° is -57.5 kJ/mol.
A) 10 B) 1.2 × 1010 C) 8.4 × 10101 D) 1.0
E) more information is needed Answer: B
38) Consider the reaction:
FeO(s) + Fe(s) + O2(g) → Fe2O3(s)
Given the following table of thermodynamic data at 298 K:
Substance ΔHf° (kJ/mol) S° ( J/K ∙ mol)
FeO(s) -271.9 60.75
Fe(s) 0 27.15
O2(g) 0 205.0
Fe2O3(s) -822.16 89.96
The value K for the reaction at 25 °C is ________.
A) 8.1 × 1019 B) 7.1 × 1085 C) 5.9 × 104 D) 370 E) 3.8 × 10-14
Answer: B
39) The normal boiling point of C2Cl3F3 is 47.6 °C and its molar enthalpy of vaporization is 27.49 kJ/mol. What is the change in entropy in the system in J/K when 28.6 grams of C2Cl3F3 vaporizes to a gas at the normal boiling point?
A) 4.19 B) -13.1 C) -4.19 D) 13.1 E) 27.5
Answer: D
40) For a given reaction with ΔS = -50.8 J/K-mol, the ΔG = 0 at 395 K. The value of ΔH must be _______ kJ/mol, assuming that ΔH and ΔS do not vary with temperature.
A) -7.78 × 10-3 B) -1.29 × 10-4 C) -20.1 D) 20.1
E) 1.29 × 10-4 Answer: C
