Acids and Bases

55. The equilibrium constant for the reaction represented by the equation below is greater than 1.0. Which of the following gives the correct relative strengths of the acids and bases in the reaction? H2PO4− + HBO32− ⇄ HPO42− + H2BO3− Acids Bases A.H2PO4− > H2BO3− and HBO32− > HPO42− B.H2BO3− > H2PO4− and HBO32¯ > HPO42− C.H2PO4− > H2BO3− and HPO42− > HBO32− D.H2BO3− > H2PO4− and HPO42− > HBO32− E.H2PO4− = H2BO3− and HPO42− = HBO32−

A

A solution of calcium hypochlorite, a common additive to swimming-pool water, is... (A) basic because of the hydrolysis of the OCl− ion (B) basic because Ca(OH)2 is a weak and insoluble base (C) neutral if the concentration is kept below 0.1 molar (D) acidic because of the hydrolysis of the Ca2+ ions (E) acidic because the acid HOCl is formed

A

HC2H3O2(aq) + CN− (aq) ⇄ HCN(aq) + C2H3O2− (aq) The reaction represented above has an equilibrium constant equal to 3.7 x 104. Which of the following can be concluded from this information? (A) CN− (aq) is a stronger base than C2H3O2− (aq) (B) HCN(aq) is a stronger acid than HC2H3O2(aq) (C) The conjugate base of CN− (aq) is C2H3O2− (aq) (D) The equilibrium constant will increase with an increase in temperature. (E) The pH of a solution containing equimolar amounts of CN− (aq) and HC2H3O2 (aq) is 7.0

A

Questions 9-12 refer to aqueous solutions containing 1:1 mole ratios of the following pairs of substances. Assume all concentrations are 1 M. (A) NH3 and NH4Cl (B) H3PO4 and NaH2PO4 (C) HCl and NaCl (D) NaOH and NH3 (E) NH3 and HC2H3O2 (acetic acid) 11. A buffer at a pH > 8

A

The net ionic equation for the reaction between silver carbonate and hydrochloric acid is... (A) Ag2CO3(s) + 2 H+ + 2 Cl− 2 AgCl(s) + H2O + CO2 (g) (B) 2 Ag+ + CO32− + 2 H+ + 2 Cl− 2 AgCl(s) + H2O + CO2(g) (C) CO32− + 2 H+ H2O + CO2(g) (D) Ag+ + Cl¯ AgCl(s) (E) Ag2CO3(s) + 2 H+ 2Ag+ + H2CO3

A

Use these answers for questions 8 - 10. (A) a solution with a pH less than 7 that is not a buffer solution (B) a buffer solution with a pH between 4 and 7 (C) a buffer solution with a pH between 7 and 10 (D) a solution with a pH greater than 7 that is not a buffer solution (E) a solution with a pH of 7 Ionization Constants CH3COOH = 1.8 x 10−5 NH3 = 1.8 x 10−5 H2CO3; K1 = 4 x 10−7 H2CO3; K2 = 4 x 10−11 8. A solution prepared to be initially 1 M in NaCl and 1 M in HCl.

A

What part of the curve corresponds to the optimum buffer action for the acetic acid/acetate pair? (A) Point V (B) Point X (C) Point Z (D) Along all of section WY (E) along all of section YZ

A

54. Which of the following is the correct equilibrium expression for the hydrolysis of CO32− ? (A) K = [HCO3− ] / ( [CO32− ] [H3O+] ) (B) K = ( [HCO3−] [OH−] ) / [CO32−] (C) K = ( [CO32− ] [OH−] ) / [HCO3−] (D) K = [CO32− ] / ( [CO2] [OH−]2 ) (E) K = ( [CO32− ] [H3O+] ) / [HCO3−]

B

8. Use these answers for questions 8 - 10. (A) a solution with a pH less than 7 that is not a buffer solution (B) a buffer solution with a pH between 4 and 7 (C) a buffer solution with a pH between 7 and 10 (D) a solution with a pH greater than 7 that is not a buffer solution (E) a solution with a pH of 7 Ionization Constants CH3COOH = 1.8 x 10−5 NH3 = 1.8 x 10−5 H2CO3; K1 = 4 x 10−7 H2CO3; K2 = 4 x 10−11 10. A solution prepared to be initially 0.5 M in CH3COOH and 1 M in CH3COONa

B

A 1-molar solution of which of the following salts has the highest pH? (A) NaNO3 (B) Na2CO3 (C) NH4Cl (D) NaHSO4 (E) Na2SO4

B

A molecule or an ion is classified as a Lewis acid if it... (A) accepts a proton from water (B) accepts a pair of electrons to form a bond (C) donates a pair of electrons to form a bond (D) donates a proton to water (E) has resonance Lewis electron-dot structures

B

A pure white crystalline solid dissolves in water to yield a basic solution that liberates a gas when excess acid is added to it. On the basis of this information, the solid could be... (A) KNO3 (B) K2CO3 (C) KOH (D) KHSO4 (E) KCl

B

At 25°C, aqueous solutions with a pH of 8 have a hydroxide ion concentration, [OH−], of... (A) 1 × 10−14 M (B) 1 × 10−8 M (C) 1 × 10−6 M (D) 1M (E) 8M

B

Commercial vinegar was titrated with NaOH solution to determine the content of acetic acid, HC2H3O2. For 20.0 milliliters of the vinegar, 32.0 milliliters of 0.500-molar NaOH solution was required. What was the concentration of acetic acid in the vinegar if no other acid was present? (A) 1.60 M (B) 0.800 M (C) 0.640 M (D) 0.600 M (E) 0.400 M

B

Equal volumes of 0.10-molar H3PO4 and 0.20-molar KOH are mixed. After equilibrium is established, the type of ion a solution in largest concentration, other than the K+ ion, is... (A) H2PO4− (B) HPO42− (C) PO43− (D) OH− (E) H3O+

B

Mixtures that would be considered buffers include which of the following? I. 0.10 M HCl + 0.10 M NaCl II. 0.10 M HF + 0.10 M NaF III. 0.10 M HBr + 0.10 M NaBr (A) I only (B) II only (C) III only (D) I and II (E) II and III

B

Questions 9-12 refer to aqueous solutions containing 1:1 mole ratios of the following pairs of substances. Assume all concentrations are 1 M. (A) NH3 and NH4Cl (B) H3PO4 and NaH2PO4 (C) HCl and NaCl (D) NaOH and NH3 (E) NH3 and HC2H3O2 (acetic acid) 12. A buffer at a pH <6

B

When dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved, This gas turned a drop of limewater, Ca(OH)2, cloudy, due to the formation of a white precipitate. The chemical was... (A) household ammonia, NH3 (B) baking soda, NaHCO3 (C) table salt, NaCl (D) epsom salts, MgSO4 . 7H2O (E) bleach, 5% NaOCl

B

When phenolphthalein is used as the indicator in a titration of an HCl solution with a solution of NaOH, the indicator undergoes a color change from clear to red at the end point of the titration. This color change occurs abruptly because... (A) phenolphthalein is a very strong acid that is capable of rapid dissociation (B) the solution being titrated undergoes a large pH change near the end point of the titration (C) phenolphthalein undergoes an irreversible reaction in basic solution (D) OH− acts as a catalyst for the decomposition of phenolphthalein (E) phenolphthalein is involved in the rate-determining step of the reaction between H3O+ and OH−

B

Which, if any, of the following species is in the greatest concentration in a 0.100-molar solution of H2SO4 in water? (A) H2SO4 molecules (B) H3O+ ions (C) HSO4− ions (D) SO42− ions (E) All species are in equilibrium and therefore have the same concentrations.

B

2 NH3 ⇄ NH4+ + NH2− In liquid ammonia, the reaction represented above occurs. In the reaction NH4+ acts as... (A) a catalyst (B) both an acid and a base (C) the conjugate acid of NH3 (D) the reducing agent (E) the oxidizing agent

C

31. H2C2O4 + 2 H2O ⇄ 2 H3O+ + C2O42− Oxalic acid, H2C2O4, is a diprotic acid with K1 = 5 x 10−2 and K2 = 5 x 10−5. Which of the following is equal to the equilibrium constant for the reaction represented above? (A) 5 x 10−2 (B) 5 x 10−5 (C) 2.5 x 10−6 (D) 5 x 10−7 (E) 2.5 x 10−8

C

56. A 0.20-molar solution of a weak monoprotic acid, HA, has a pH of 3.00. The ionization constant of this acid is... (A) 5.0 x 10−7 (B) 2.0 x 10−7 (C) 5.0 x 10−6 (D) 5.0 x 10−3 (E) 2.0 x 10−3

C

Correct procedures for a titration include which of the following? I. Draining a pipet by touching the tip to the side of the container used for the titration II. Rinsing the buret with distilled water just before filling it with the liquid to be titrated III. Swirling the solution frequently during the titration (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

C

How can 100. mL of sodium hydroxide solution with a pH of 13.00 be converted to a sodium hydroxide solution with a pH of 12.00? (A) By diluting the solution with distilled water to a total volume of 108 mL (B) By diluting the solution with distilled water to a total volume of 200 mL (C) By diluting the solution with distilled water to a total volume of 1.00 L (D) By adding 100. mL of 0.10 M HCl (E) By adding 100. mL of 0.10 M NaOH

C

In the titration of a weak acid of unknown concentration with a standard solution of a strong base, a pH meter was used to follow the progress of the titration. Which of the following is true for this experiment? (A) The pH is 7 at the equivalence point. (B) The pH at the equivalence point depends on the indicator used. (C) The graph of pH versus volume of base added rises gradually at first and then much more rapidly. (D) The graph of pH versus volume of base added shows no sharp rise. (E) The [H+] at the equivalence point equals the ionization constant of the acid.

C

Questions 9-12 refer to aqueous solutions containing 1:1 mole ratios of the following pairs of substances. Assume all concentrations are 1 M. (A) NH3 and NH4Cl (B) H3PO4 and NaH2PO4 (C) HCl and NaCl (D) NaOH and NH3 (E) NH3 and HC2H3O2 (acetic acid) 9. The solution with the lowest Ph

C

To determine the molar mass of a solid monoprotic acid, a student titrated a weighed sample of the acid with standardized aqueous NaOH. Which of the following could explain why the student obtained a molar mass that was too large? I. Failure to rinse all acid from the weighing paper into the titration vessel II. Addition of more water than was needed to dissolve the acid III. Addition of some base beyond the equivalence point (A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III

C

What volume of 0.150-molar HCl is required to neutralize 25.0 milliliters of 0.120-molar Ba(OH)2? (A) 20.0 mL (B) 30 0 mL (C) 40.0 mL (D) 60.0 mL (E) 80.0 mL

C

49. Each of the following can act as both a Brönsted acid and a Brönsted base EXCEPT... (A) HCO3− (B) H2PO4− (C) NH4+ (D) H2O (E) HS−

D

Acid Acid Dissociation Constant, Ka H3PO4 7 x 10−3 H2PO4− 8 x 10−8 HPO42− 5 x 10−13 On the basis of the information above, a buffer with a pH = 9 can best be made by using... (A) pure NaH2PO4 (B) H3PO4 + H2PO4− (C) H2PO4− + PO43− (D) H2PO4− + HPO42− (E) HPO42− + PO43−

D

All of the following species can function as Brönsted-Lowry bases in solution EXCEPT... (A) H2O (B) NH3 (C) S2− (D) NH4+ (E) HCO3−

D

The graph below shows the titration curve that results when 100. mL of 0.0250 M acetic acid is titrated with 0.100 M NaOH. Which of the following indicators is the best choice for this titration? pH Range of Color Change (A) Methyl orange 3.2 - 4.4 (B) Methyl red 4.8 - 6.0 (C) Bromthymol blue 6.1 - 7.6 (D) Phenolphthalein 8.2 - 10.0

D

The pH of 0.1-molar ammonia is approximately... (A) 1 (B) 4 (C) 7 (D) 11 (E) 14

D

The safest and most effective emergency procedure to treat an acid splash on skin is to do which of the following immediately? (A) Dry the affected area with paper towels (B) Sprinkle the affected area with powdered Na2SO4(s) (C) Flush the affected area with water and then with a dilute NaOH solution (D) Flush the affected area with water and then with a dilute NaHCO3 solution (E) Flush the affected area with water and then with a dilute vinegar solution

D

Use these answers for questions 8 - 10. (A) a solution with a pH less than 7 that is not a buffer solution (B) a buffer solution with a pH between 4 and 7 (C) a buffer solution with a pH between 7 and 10 (D) a solution with a pH greater than 7 that is not a buffer solution (E) a solution with a pH of 7 Ionization Constants CH3COOH = 1.8 x 10−5 NH3 = 1.8 x 10−5 H2CO3; K1 = 4 x 10−7 H2CO3; K2 = 4 x 10−11 9. A solution prepared to be initially 1 M in Na2CO3 and 1 M in CH3COONa

D

What is the H+(aq) concentration in 0.05 M HCN(aq) ? (The Ka for HCN is 5.0 x 10−10) (A) 2.5 x 10−11 (B) 2.5 x 10−10 (C) 5.0 x 10−10 (D) 5.0 x 10−6 (E) 5.0 x 10−4

D

What is the pH of a 1.0 x 10−2-molar solution of HCN? (Ka = 4.0 x 10 −10 ) (A) 10 (B) Between 7 and 10 (C) 7 (D) Between 4 and 7 (E) 4

D

. Which of the following ions is the strongest Lewis acid? (A) Na+ (B) Cl− (C) CH3COO− (D) Mg2+ (E) Al3+

E

22. HSO4− + H2O ⇄ H3O+ + SO42− In the equilibrium represented above, the species that act as bases include which of the following? I. HSO4− II. H2O III. SO42− (A) II only (B) III only (C) I and II (D) I and III (E) II and III

E

As the number of oxygen atoms increases in any series of oxygen acids, such as HXO, HXO2, HXO3, ...., which of the following is generally true? (A) The acid strength varies unpredictably. (B) The acid strength decreases only if X is a nonmetal. (C) The acid strength decreases only if X is a metal. (D) The acid strength decreases whether X is a nonmetal or a metal. (E) The acid strength increases.

E

Ascorbic acid H2C6H6O6(s), is a diprotic acid with K1 = 7.9 × 10−5 and K2 = 1.6 × 10−12. In a 0.005 M aqueous solution of ascorbic acid, which of the following species is present in the lowest concentration? (A) H2O(l) (B) H3O+(aq) (C) H2C6H6O6(aq) (D) HC6H6O6−(aq) (E) C6H6O62−(aq)

E

If the acid dissociation constant, Ka, for an acid HA is 8 x 10−4 at 25 °C, what percent of the acid is dissociated in a 0.50-molar solution of HA at 25 °C? (A) 0.08% (B) 0.2% (C) 1% (D) 2% (E) 4%

E

Questions 9-12 refer to aqueous solutions containing 1:1 mole ratios of the following pairs of substances. Assume all concentrations are 1 M. (A) NH3 and NH4Cl (B) H3PO4 and NaH2PO4 (C) HCl and NaCl (D) NaOH and NH3 (E) NH3 and HC2H3O2 (acetic acid) 10. The most nearly neutral solution

E

The net ionic equation for the reaction that occurs during the titration of nitrous acid with sodium hydroxide is... (A) HNO2 + Na+ + OH− NaNO2 + H2O (B) HNO2 + NaOH Na+ + NO2− + H2O (C) H+ + OH− H2O (D) HNO2 + H2O NO2− + H3O+ (E) HNO2 + OH− NO2− + H2O

E

Which of the following acids can be oxidized to form a stronger acid? (A) H3PO4 (B) HNO3 (C) H2CO3 (D) H3BO3 (E) H2SO3

E

Which of the following reactions does NOT proceed significantly to the right in aqueous solutions? (A) H3O+ + OH− 2 H2O (B) HCN + OH− H2O + CN− (C) Cu(H2O)42+ + 4 NH3 Cu(NH3)42+ + 4H2O (D) H2SO4 + H2O H3O+ + HSO4− (E) H2O + HSO4− H2SO4 + OH−

E