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CH142 Sample Exam 2 Questions
Multiple Choice
1) According to the Arrhenius concept, an acid is a substance that ________.
A) is capable of donating one or more H+
B) causes an increase in the concentration of H+ in aqueous solutions C) can accept a pair of electrons to form a coordinate covalent bond D) reacts with the solvent to form the cation formed by autoionization of that solvent E) tastes bitter
2) 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) increases [OH-‐‑] when placed in H2O
D) acts as a proton acceptor E) acts as a proton donor
3) Which below best describes the behavior of an amphoteric hydroxide in water?
A) Dissolves in NaOH only B) Dissolves in HCl only C) Forms a precipitate in NaOH only D) Forms a precipitate in HCl only E) Dissolves in NaOH or HCl
4) Which one of the following statements regarding Kw is false?
A) pKw is 14.00 at 25 °C.
B) The value of Kw is always 1.0 × 10-‐‑14. C) Kw changes with temperature.
D) The value of Kw shows that water is a weak acid. E) Kw is known as the ion product of water.
5) Of the following acids, ________ is a strong acid.
A) HNO2 B) H2CO3 C) HNO3 D) HClO E) HF
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6) Which one of the following is the weakest acid? A) HF (Ka = 6.8 × 10-‐‑4)
B) HClO (Ka = 3.0 × 10-‐‑8)
C) HNO2 (Ka = 4.5 × 10-‐‑4)
D) HCN (Ka = 4.9 × 10-‐‑10)
E) Acetic acid (Ka = 1.8 × 10-‐‑5) 7) In which one of the following solutions is silver chloride the most soluble?
A) 0.181 M HCl B) 0.0176 M NH3 C) 0.744 M AgNO3 D) pure water E) 0.181 M NaCl
8) HA is a weak acid. Which equilibrium corresponds to the equilibrium constant Kb for A-‐‑?
A) HA (aq) + H2O (l) H2A+ (aq) + OH-‐‑(aq)
B) A-‐‑ (aq) + H3O+ (aq) HA (aq) + H2O (l)
C) HA (aq) + OH-‐‑ (aq) H2O (l) + H+ (aq)
D) A-‐‑ (aq) + H2O (l) HA (aq) + OH-‐‑ (aq)
E) A-‐‑ (aq) + OH-‐‑ (aq) HOA2-‐‑ (aq) 9) Using the data in the table, which of the conjugate bases below is the strongest base?
A) OAc-‐‑
B) C7H5O2-‐‑
C) NO2-‐‑
D) F-‐‑ E) HNO2
10. Which species is a Lewis base?
Cl− + BCl3 ! BCl4−
A) Cl− B) BCl3 C) BCl4− D) All of the above
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11) Which of the following aqueous solutions has the highest [OH-‐‑]? A) a solution with a pH of 3.0 B) a 1 × 10-‐‑4 M solution of HNO3 C) a solution with a pOH of 12.0 D) pure water E) a 1 × 10-‐‑3 M solution of NH4Cl
12) A 0.0035 M aqueous solution of a particular compound has pH = 2.46. The compound is ________.
A) a weak base B) a weak acid C) a strong acid D) a strong base E) a salt
13) In acidic solution, ________.
A) [H3O+] > [OH-‐‑]
B) [H3O+] = [OH-‐‑]
C) [H3O+] < [OH-‐‑]
D) [OH-‐‑] > 7.00 E) [H3O+] = 0M
14) Hydrochloric acid is a strong acid. This means that ________.
A) HCl dissociates completely to H+(aq) and Cl-‐‑(aq) when it dissolves in water B) HCl does not dissociate at all when it is dissolved in water C) HCl produces a gaseous product when it is neutralized D) HCl cannot be neutralized by a weak base E) aqueous solutions of HCl contain equal concentrations of H+(aq) and OH-‐‑(aq)
15) Of the following, which is the strongest acid?
A) HIO4 B) HIO3 C) HIO2 D) HIO E) The acid strength of all of the above is the same.
16) What is the conjugate acid of NH3?
A) NH3
B) NH2+
C) NH3+
D) NH4+
E) NH4OH
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17) Which of the following could be added to a solution of sodium acetate to produce a buffer? A) acetic acid only B) acetic acid or hydrochloric acid C) hydrochloric acid only D) potassium acetate only E) sodium chloride or potassium acetate
18) What change will be caused by addition of a small amount of HCl to a solution containing fluoride ions and 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 hydrogen fluoride will decrease and the concentration of fluoride ions will increase. D) The concentration of fluoride ion will decrease and the concentration of hydrogen fluoride will increase. E) The fluoride ions will precipitate out of solution as its acid salt.
19) Of the following solutions, which has the greatest buffering capacity?
A) 0.521 M HC2H3O2 and 0.217 M NaC2H3O2 B) 0.821 M HC2H3O2 and 0.713 M NaC2H3O2 C) 0.365M HC2H3O2 and 0.497 M NaC2H3O2 D) 0.121 M HC2H3O2 and 0.116 M NaC2H3O2 E) They are all buffer solutions and would all have the same capacity.
20) A 25.0 mL sample of a solution of an unknown compound is titrated with a 0.115 M NaOH solution. The titration curve here was obtained. The unknown compound is ________.
A) a strong acid B) a strong base C) a weak acid D) a weak base E) neither an acid nor a base
21) Cyanide ion forms very stable complex ions with several metal ions. What is the concentration of free
Ag+(aq) in a solution that initially contains 1.3 mol of Ag(CN)2-‐‑ per liter of solution? Kf for Ag(CN)2-‐‑ is 4.5 x 1010.
A) 5.2 x 103 M B) 7.3 x 10-‐‑12 M C) 1.9 x 10-‐‑4 M D) 2.7 x 10-‐‑6 M E) 3.1 x 10-‐‑4 M
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22) Which compound listed below has the greatest molar solubility in water?
A) Ag3PO4 (Ksp = 1.8 x 10-‐‑18) B) CdCO3 (Ksp = 5.2 x 10-‐‑12) C) Cd(OH)2 (Ksp = 2.5 x 10-‐‑14) D) Sr3(PO4)2 (Ksp = 1.0 x 10-‐‑31) E) ZnCO3 Ksp = 1.4 x 10-‐‑11)
23) The molar solubility of ________ is not affected by the pH of the solution.
A) Na3PO4 B) NaF C) KNO3 D) AlCl3 E) Ca(OH)2
24) A solution is prepared by dissolving 0.23 mol of benzoic acid and 0.27 mol of sodium benzoate in
water sufficient to yield 1.00 L of solution. The addition of 0.05 mol of NaOH to this buffer solution causes the pH to increase slightly. The pH does not increase drastically because the NaOH reacts with the ________ present in the buffer solution. The Ka of benzoic acid is 6.3 × 10-‐‑5.
A) H2O
B) H3O+
C) benzoate D) benzoic acid E) This is a buffer solution: the pH does not change upon addition of acid or base.
25) Which is the correct Ksp expression for PbCl2 (s) dissolving in water?
A) Ksp = [Pb2+] [Cl–]2
B) Ksp = [Pb2+] [Cl–]
C) Ksp = [Pb2+]2 [Cl–]
D) Ksp = [PbCl+] [Cl–]
E) Ksp = [Pb+] [Cl2–]2
26) A solution of NaF is added dropwise to a solution that is 0.0122 M in Ba2+. When the concentration of
F-‐‑ exceeds ________ M, BaF2 will precipitate. Neglect volume changes. For BaF, Ksp = 1.7 × 10-‐‑6.
A) 7.0 × 10-‐‑5
B) 1.2 × 10-‐‑2
C) 2.1 × 10-‐‑8
D) 3.0 × 10-‐‑3
E) 1.4 × 10-‐‑4
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27) The base-‐‑dissociation constant, Kb, for pyridine, C5H5N, is 1.4 × 10-‐‑9. The acid-‐‑dissociation constant,
Ka, for the pyridinium ion, C5H5NH+, is ________.
A) 1.0 × 10-‐‑7
B) 1.4 × 10-‐‑23 C) 7.1 × 10-‐‑4
D) 1.4 × 10-‐‑5
E) 7.1 × 10-‐‑6
28) 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) 1.705 B) 0.851 C) 3.406 D) 4.201 E) 2.383
29) What is the concentration (in M) of hydroxide ions in a solution at 25.0 °C with pH = 4.282?
A) 4.28 B) 9.72 C) 1.92 × 10-‐‑10
D) 5.22 × 10-‐‑5 E) none of the above
30) A 25.0 mL sample of a solution of a monoprotic acid is titrated with a 0.115 M NaOH solution. The titration curve below was obtained. Which of the following indicators would be best for this titration?
A) methyl red B) bromthymol blue C) thymol blue D) phenolpthalein E) bromocresol purple
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31) The following observations are made about a diprotic acid H2A: (i) A 0.10 M solution of H2A has pH 3.30. (ii) A 0.10 M solution of the salt NaHA is acidic. Which of the following could be the value of pKa2 for H2A:
A) 3.22 B) 5.30 C) 7.47 D) 9.82
Short Answer 1) You have a solution of 3.98 × 10-‐‑9 M HCl at 25°C.
a) What is the pH? b) What is the pOH? 2) You have a solution of 0.100 M NaOH at 25°C. What is the pH of the solution?
a) What is the pH? b) What is the pOH? 3) HZ is a weak acid. An aqueous solution of HZ is prepared by dissolving 0.020 mol of HZ in sufficient
water to yield 1.0 L of solution. The pH of the solution was 4.93 at 25.0 °C. What is the Ka of HZ? 4) 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.
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5) The Ka of hypochlorous acid (HClO) is 3.00 × 10-‐‑8. What is the pH at 25.0 °C of an aqueous solution that is 0.020 M in HClO?
6) A 0.15 M aqueous solution of the weak base B at 25.0 °C has a pH of 8.88. What is Kb for B? 7) An aqueous solution contains 0.050 M of methylamine. What is the concentration of H+ in this
solution? Kb for methylamine is 4.4 × 10-‐‑4. 8) What is the pH of a solution prepared by dissolving 0.350 mol of solid methylamine hydrochloride
(CH3NH3Cl) in 1.00 L of 1.10 M methylamine (CH3NH2)? The Kb for methylamine is
4.40 × 10-‐‑4. (Assume the final volume is 1.00 L.) 9) What is the pH of a solution prepared by mixing 50.0 mL of 0.125 M KOH and 50.0 mL of 0.125 M HCl?
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10) A 50.0 mL sample of an aqueous H2SO4 solution is titrated with a 0.375 M NaOH solution. Complete titration requires 62.5 mL of the base. What is the concentration of H2SO4?
11) A 25.0 mL sample of 0.723 M HClO4 is titrated with a 0.27 M KOH solution. What is the H3O+
concentration after the addition of 80.0 mL of KOH? 12) What is the concentration of iodide ions in a saturated solution of lead (II) iodide? The solubility
product constant of PbI2 is 1.4 × 10-‐‑8. 13) The solubility of lead (II) chloride (PbCl2) is 1.6 × 10-‐‑2 M. What is the Ksp of PbCl2? 14) Calculate the maximum concentration of silver ions (Ag+) in a solution that contains 0.025 M of CO32-‐‑.
The Ksp of Ag2CO3 is 8.1 × 10-‐‑12.
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15) The Ksp for Zn(OH)2 is 5.0 × 10-‐‑17. Determine the solubility of Zn(OH)2 in a buffer solution with a pH of 11.5.
16) Consider a solution containing 0.100 M fluoride ions and 0.126 M hydrogen fluoride. What is the
concentration of fluoride ions after the addition of 9.00 mL of 0.0100 M HCl to 25.0 mL of this solution?
17) How many milliliters of 0.0839 M NaOH are required to titrate 25.0 mL of 0.0990 M HBr to the
equivalence point? 18) A 25.0-‐‑mL sample of 0.150 M hypochlorous acid is titrated with a 0.150 M NaOH solution. What is the
pH after 12.5 mL of base is added? The Ka of hypochlorous acid is 3.0 × 10-‐‑8.
19) The Ka for formic acid (HCO2H) is 1.8 × 10-‐‑4. What is the pH of a 0.20 M aqueous solution of sodium
formate (NaHCO2)?
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20) The Ka of hypochlorous acid (HClO) is 3.0 × 10-‐‑8 at 25 °C. What is the percent ionization of
hypochlorous acid in a 0.015 M aqueous solution of HClO at 25 °C? 21) Indicate whether each of the following statements is true or false. For each statement that is false,
correct the statement to make it true.
a) In general, the acidity of binary acids increases from left to right across the periodic table. T F
b) In a series of acids that have the same central atom, acid strength increases with the number of hydrogen atoms bonded to the central atom. T F
c) H2Te is a stronger acid than H2S because Te is more electronegative than S. T F 22) Explain the following observations:
a) HNO3 is a stronger acid than HNO2
b) H2S is a stronger acid than H2O
c) H2SO4 is a stronger acid than HSO4¯ˉ
d) H2SO4 is a stronger acid than H2SeO4
e) CCl3COOH is a stronger acid than CH3COOH 23) The odor of fish is due primarily to amines, especially methylamine (CH3NH2). Fish is often served
with a wedge of lemon, which contains citric acid. The amine and the acid react forming a product with no odor, thereby making the less-‐‑than-‐‑fresh fish more appetizing. Ka1 for citric acid is 7.4x10-‐‑4 and Kb for methylamine is 4.4x10-‐‑4. Calculate the equilibrium constant for the reaction of citric acid with methylamine, if only the first proton of citric acid (Ka1) is important in the neutralization reaction.
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24) A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point.
a) What is the molar mass of the acid? b) After 7.25 mL of base had been added in the titration, the pH was found to be 2.85. What is the Ka
for the unknown acid? 25) Assume that you make up a buffer solution using lactic acid (HC3H5O3; 90.1 g/moles; pKa= 3.86). You
add 0.23 grams of lactic acid and enough water to bring the volume to 25 mL. What volume of a 1.00 M NaOH solution must be added to the solution to produce a buffer with pH = 4.16?
26) Will Ag2SO4 precipitate when 100 mL of 0.050 M AgNO3 is mixed with 10 mL of 0.050 M Na2SO4
solution? Ksp for Ag2SO4 is 1.5x10-‐‑5. You must show your work.