1092-2nd Midterm Exam _05/19/21_(A)
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) A Br nsted-Lowry base is defined as a substance that ________.
A) increases [H+] when placed in H2O B) decreases [H+] when placed in H2O C) acts as a proton acceptor
D) acts as a proton donor
E) increases [OH-] when placed in H2O Answer: C
2) Which one of the following is a Br nsted-Lowry base?
A) HNO2 B) CH3COOH C) HF
D) (CH3)3N
E) none of the above Answer: D
3) The conjugate base of HPO42- is ________.
A) H2PO4- B) PO43- C) H2PO4 D) H3PO4
E) none of the above Answer: B
4) Calculate the pH of a 0.500 M aqueous solution of NH3. The Kb of NH3 is 1.77 × 10-5.
A) 2.53 B) 8.95 C) 11.77 D) 2.23 E) 11.47
Answer: E
5) The Ka for some acid HA is 7.0 × 10-4. What is the pH of a 0.15 M aqueous solution prepared by the salt NaA?
A) 5.83 B) 0.82 C) 1.17 D) 5.01 E) 8.17
Answer: E
6) The pH of a 0.25 M aqueous solution of hydrofluoric acid, HF, at 25.0 °C is 2.03. What is the value of Ka for HF?
A) 3.6 × 10-4 B) 2.0 × 10-9 C) 1.1 × 10-9 D) 6.0 × 10-5
E) none of the above Answer: A
7) The acid-dissociation constants of sulfurous acid (H2SO3) are Ka1 = 1.7 × 10-2 and Ka2 = 6.4 × 10-8 at 25.0
°C. Calculate the pH of a 0.163 M aqueous solution of sulfurous acid.
A) 1.28 B) 6.21 C) 4.53 D) 1.93 E) 1.86
Answer: A
8) Calculate the percent ionization of formic acid (HCO2H) in a solution that is 0.152 M in formic acid. The Ka of formic acid is 1.8 × 10-4.
A) 3.44 B) 8.44 C) 0.0180 D) 2.74 × 10-5 E) 0.581
Answer: A
9) In which of the following aqueous solutions does the weak acid exhibit the highest percentage ionization?
A) 0.01 M H2CO3 (Ka = 4.5 × 10-7) B) 0.01 M HOCl (Ka = 3.5 × 10-8) C) 0.01 M HCN (Ka = 6.2 × 10-10) D) 0.01 M HC3H5O2 (Ka = 1.3 × 10-5)
E) 0.01 M H2SO3 (Ka = 1.4 × 10-2) Answer: E
10) Of the following substances, an aqueous solution of ________ will form basic solutions.
NH4Br Pb(NO3)2 K2CO3 NaF
A) K2CO3, NH4Br B) NH4Br only C) NaF, K2CO3 D) NaF only
E) NH4Br, Pb(NO3)2 Answer: C
11) For which salt should the aqueous solubility be most sensitive to pH?
A) MgI2 B) MgCl2 C) MgF2 D) Mg(NO3)2 E) MgBr2
Answer: C
12) Which of the following acids will be the strongest?
A) H2SeO4 B) H2SO4 C) HSO3- D) HSO4- E) H2SO3
Answer: B
13) A solution containing which one of the following pairs of substances will be a buffer solution?
A) KBr, HBr B) NaI, HI C) CsF, HF D) RbCl, HCl
E) none of the above Answer: C
14) What change will be caused by addition of a small amount of HCl to a solution containing 0.1 M fluoride ions and 0.1 M hydrogen fluoride?
A) The concentration of hydronium ions will increase significantly.
B) The concentration of fluoride ions will increase as will the concentration of hydronium ions.
C) The concentration of fluoride ion will decrease and the concentration of hydrogen fluoride will increase.
D) The fluoride ions will precipitate out of solution as its acid salt.
E) The concentration of hydrogen fluoride will decrease and the concentration of fluoride ions will increase.
Answer: C
15) Which solution would have the greatest buffering capacity?
A) 1.15 M HF and 0.624 M NaF B) 0.574 M HF and 0.312 M NaF C) 0.287 M HF and 0.156 M NaF D) 0.189 M HF and 0.103 M NaF
E) They are all buffer solutions and would all have the same capacity.
Answer: A
16) The Ka of some weak acid HA is 1.76 × 10-5. The pH of a buffer prepared by combining 15.0 mL of 1.00 M A- and 50.0 mL of 1.00 M HA is ________.
A) 0.851 B) 1.705 C) 3.406 D) 4.232 E) 2.383
Answer: D
17) 1.A 25.0 mL sample of 0.150 M acetic acid is titrated with a 0.150 M NaOH solution. What is the pH at the equivalence point? The Ka of acetic acid is 1.8 × 10-5.
A) 11.74 B) 9.26 C) 8.81 D) 7.00 E) 4.74
Answer: C
18) A 50.0 mL sample of an aqueous H2SO4 solution is titrated with a 0.375 M NaOH solution. The complete neutralization is reached with 62.5 mL of the base. The concentration of H2SO4 is ________ M.
A) 0.469 B) 0.300 C) 0.938 D) 0.234 E) 0.150
Answer: D
19) Use the information below to answer the question below
:
methyl orange: red at pH < 3.1: orange at pH 3.1-4.4
litmus: red at pH < 4.5: purple at pH 4.5-8.3: blue above pH 8.3
thymol blue: yellow at pH < 8.0: green at pH 8.0-9.6: blue above pH 9.6
trinitrobenzene: colorless at pH < 12: yellow at pH 12.0-1: orange above pH 14.0
Which of the pH indicators from the list above would be most appropriate for the titration of 0.30 M acetic acid (Ka = 1.8 × 10-5) with 0.15 M sodium hydroxide?
A) litmus
B) trinitrobenzene C) thymol blue D) methyl orange
E) Both thymol blue and trinitrobenzene can be used.
Answer: C
20) A solution contains 1.0 x 10-2 M Ag+ and 2.0 x 10-2 M Pb2+. When the concentration of Cl- is 2 x 10-5 M, is precipitation observed? (AgCl Ksp = 1.8 x 10-10, PbCl2 Ksp = 1.7 x 10-5)
A) only AgCl B) only PbCl2
C) both AgCl and PbCl2 D) no precipitate
Answer: A
21) Which one of the following is not amphoteric?
A) Ca(OH)2 B) Cr(OH)3 C) Zn(OH)2 D) Sn(OH)2 E) Al(OH)3
Answer: A
22) The molar solubility of ________ is not affected by the pH of the solution.
A) Na3PO4 B) MnS C) AlCl3 D) NaF E) KNO3
Answer: E
23) The solubility of manganese (II) hydroxide (Mn(OH)2) is 2.2 × 10-5 M. What is the Ksp of Mn(OH)2?
A) 4.8 × 10-10 B) 4.3 × 10-14 C) 2.2 × 10-5 D) 1.1 × 10-14 E) 2.1 × 10-14 Answer: B
24) Which compound listed below has the smallest molar solubility in water?
A) CaF2 (Ksp = 3.9 × 10-11) B) Cd(OH)2 (Ksp = 2.5 × 10-14) C) AgI (Ksp = 8.3 × 10-17) D) ZnCO3 (Ksp = 1.4 × 10-11)
E) CdCO3 (Ksp = 5.2 × 10-12) Answer: C
25) In which of the following aqueous solutions would you expect PbCl2 to have the lowest solubility? (The Ksp of PbCl2 is 1.7 x × 10-5)
A) 0.020 M Pb(NO3)2 B) pure water C) 0.020 M KCl D) 0.020 M BaCl2
E) 0.020 M NaCl Answer: D
26) The thermodynamic quantity that expresses the extent of randomness in a system is ________.
A) heat flow B) bond energy C) enthalpy D) internal energy
E) entropy Answer: E
27) Place the following in order of increasing entropy at 298 K.
Ne Xe He Ar Kr
A) Ar < Ne < Xe < Kr < He B) He < Ne < Ar < Kr < Xe C) Xe < Kr < Ar < Ne < He D) He < Kr < Ne < Ar < Xe E) Ar < He < Ar < Ne < Kr Answer: B
28) Which one of the following processes produces a decrease of the entropy of the system?
A) dissolving sodium chloride in water B) boiling of alcohol
C) sublimation of naphthalene D) explosion of nitroglycerine
E) dissolving oxygen in water Answer: E
29) S is positive for the reaction ________.
A) HCl (g) + NH3 (g) NH4Cl (s) B) Pb2+ (aq) + 2Cl- (aq) PbCl2 (s) C) CO2 (g) CO2 (s)
D) 2 Ca (s) + O2 (g) 2 CaO (s) E) 2 KClO3 (s) 2KCl (s) + 3 O2 (g) Answer: E
30) For an isothermal process, the entropy change of the surroundings is given by the equation:
A) S = -qsys / T B) S = -qsys T C) S = qsys T D) S = -q lnT E) S = q lnT Answer: A
31) Of the following, only ________ is not a state function.
A) H B) S C) q D) E E) T
Answer: C 32) For the reaction
C2H6 (g) C2H4 (g) + H2 (g)
H° is +137 kJ/mol and S° is +120 J/K · mol. This reaction is ________.
A) nonspontaneous at all temperatures B) spontaneous at all temperatures C) spontaneous only at low temperature D) spontaneous only at high temperature Answer: D
33) What is the value of S° for the formation of POCl3 from its constituent elements,?
P2 (g) + O2 (g) + 3Cl2 (g) 2POCl3 (g)
Thermodynamic Quantities for Selected Substances at 298.15 K (25 °C) Substance H°f (kJ/mol) G°f (kJ/mol) S° (J/K-mol)
Cl2 (g) 0 0 222.96
O2 (g) 0 0 205.0
P2 (g) 144.3 103.7 218.1
POCl3 (g) -542.2 -502.5 325
A) +321.0 B) -771.0 C) +771.0 D) -442.0 E) -321.0
Answer: D
34) Which of the following statements is true?
A) Processes are spontaneous because they occur at an observable rate.
B) Processes that are spontaneous in one direction are spontaneous in the opposite direction.
C) Spontaneity can depend on the temperature.
D) All of the statements are true.
Answer: C
35) Which one of the following statements is true about the equilibrium constant for a reaction if G° for the reaction is negative?
A) K < 1 B) K = 0 C) K = 1 D) K > 1
E) More information is needed.
Answer: D
36) The standard Gibbs free energy of formation of ________ is zero.
(a) H2O (l) (b) Fe (s) (c) I2 (s) A) (a) only
B) (b) only C) (c) only D) (b) and (c)
E) (a), (b), and (c) Answer: D
37) Calculate Grxn at 298 K under the conditions shown below for the following reaction. (R: 8.314 J/mol · K)
3 O2(g) 2 O3(g) G° = +326 kJ
P(O2) = 0.41 atm, P(O3) = 5.2 atm
A) +341 kJ B) +332 kJ C) -109 kJ D) +17.8 kJ E) -47.4 kJ
Answer: A
38) The Gibbs energy change for a reaction is -298 kJ. The reaction is therefore:
A) endothermic B) exothermic C) nonspontaneous D) irreversible
E) spontaneous Answer: E
39) Which of the following reactions will have the largest equilibrium constant (K) at 298 K?
A) 2 Hg(g) + O2(g) 2 HgO(s) G° = -180.8 kJ B) Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g) G° = -28.0 kJ
C) 3 O2(g) 2 O3(g) G° = +326 kJ
D) CaCO3(s) CaO(s) + CO2(g) G° =+131.1 kJ E) It is not possible to determine without more information.
Answer: A
40) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for the reaction:
(R: 8.314 J/mol · K)
2 SO2 (g) + O2 (g) 2 SO3 (g) Substance Hf° (kJ/mol) S° (J/mol · K)
SO2 (g) -297 249
O2 (g) 0 205
SO3 (g) -395 256
A) 2.40 × 1024 B) 1.06 C) 3.82 × 1023 D) 1.95
E) More data are needed.
Answer: A
