Deck 13: Aqueous Equilibria

Question 1

What is the pH of an aqueous solution that is 0.011 M HF (K_a = 3.5 * 10^-4)and 0.015 M NaF?

A)1.95
B)3.46
C)3.59
D)5.27
E)3.33

Answer 1

3.59

Question 2

Calculate the [H⁺] in an aqueous solution that is 0.0755 M HF and 0.100 M NaF.The value of K_a for HF is 3.5 * 10^-4.

A)4.6 * 10^-4 M
B)2.6 *10^-4 M
C)3.5 * 10^-4 M
D)0.176 M
E)0.0755 M

Answer 2

2.6 *10^-4 M

Question 3

A solution is prepared by mixing equal volumes of 0.40 M HF(aq)with 0.20 M KOH(aq).This solution is a buffer.

Answer 3

True

Question 4

The pH of 0.50 M HNO₂(aq)is 1.8.Therefore,the pH of a solution that is 0.50 M HNO₂(aq)and 0.10 M KNO₂(aq)is greater than 1.8.

Question 5

What is the pH of an aqueous solution that is 0.60 (CH₃)₃N (K_b = 6.5 * 10^-5)and 0.95 M (CH₃)₃NHCl?

A)4.39
B)10.01
C)3.99
D)9.81
E)9.61

Question 6

What is the pH of an aqueous solution that is 0.10 M HCOOH (K_a =1.8 * 10^-4)and 0.10 M NaHCO₂?

A)10.26
B)3.74
C)5.74
D)2.38
E)5.62

Question 7

What is the pH of an aqueous solution that is 0.018 M C₆H₅NH₂ (K_b = 4.3 * 10^-10)and 0.12 M C₆H₅NH₃Cl?

A)5.46
B)4.63
C)3.81
D)10.19
E)8.54

Question 8

Choose the effective pH range of an aniline/anilinium chloride buffer.The value of the K_b for aniline is 4.3 * 10^-10.

A)3.6-5.6
B)8.4-10.4
C)1.1-3.1
D)5.1-7.1
E)10.1-12.1

Question 9

Calculate the [OH^-] in an aqueous solution that is 0.125 M NH₃ and 0.125 M NH₄Cl.The value of K_b for NH₃ is 1.8 * 10^-5.

A)1.8 * 10^-5 M
B)5.5 * 10^-10 M
C)6.7 * 10^-12 M
D)0.125 M
E)1.5 *10^-3 M

Question 10

Choose the effective pH range of a HF/NaF buffer.For HF,K_a = 3.5 * 10^-4.

A)6.0-8.0
B)9.6-11.6
C)5.0-7.0
D)0.7-2.7
E)2.5-4.5

Question 11

What is the pH of an aqueous solution that is 1.0 M HClO (K_a = 3.0 *10^-8)and 0.75 M NaClO?

A)7.64
B)7.40
C)6.36
D)7.52
E)6.60

Question 12

What is the pH of an aqueous solution that is 0.20 M HNO₂ (K_a = 4.3 * 10^-4)and 0.20 M NaNO₂?

A)3.67
B)2.37
C)3.37
D)4.39
E)10.63

Question 13

Calculate the [OH^-] in an aqueous solution that is 0.125 M NH₃ and 0.300 M NH₄Cl.The value of K_b for NH₃ is 1.8 *10^-5.

A)0.425 M
B)0.125 M
C)1.8 * 10^-5 M
D)7.5 *10^-6 M
E)4.3 * 10^-5 M

Question 14

When sodium nitrite is added to HNO₂(aq),

A)the equilibrium concentration of HCOOH(aq)decreases.
B)the pH of the solution increases.
C)the K_a increases.
D)the pH of the solution does not change.
E)the pH of the solution decreases.

Question 15

A solution is prepared by mixing equal volumes of 0.40 M HF(aq)with 0.40 M KOH(aq).This solution is a buffer.

Question 16

What is the pH of an aqueous solution that is 0.12 M C₆H₅NH₂ (K_b = 4.3 * 10^-10)and 0.018 M C₆H₅NH₃Cl?

A)5.46
B)10.19
C)4.63
D)3.81
E)8.54

Question 17

Choose the effective pH range of a pyridine/pyridinium chloride buffer? For pyridine,the value of K_b is 1.8 * 10^-9.

A)9.1-11.1
B)1.4-3.4
C)10.3-12.3
D)7.7-9.7
E)4.3-6.3

Question 18

What is the main factor that directly determines the pH of any buffer?

Question 19

When pyridinium chloride is added to C₅H₅N(aq),

A)the pH of the solution does not change.
B)the pH of the solution increases.
C)the pH of the solution decreases.
D)the K_b increases.
E)the equilibrium concentration of NH₃(aq)decreases.

Question 20

The pH of 0.30 M CH₃NH₂(aq)is 12.0.Therefore,the pH of a solution that is 0.30 M CH₃NH₂(aq)and 0.10 M CH₃NH₃Cl(aq)is greater than 12.0.

Question 21

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of HCl is added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

A)4.70
B)4.84
C)4.75
D)4.80
E)4.66

Question 22

For pyridine,pK_b = 8.75.What is the pH of an aqueous buffer solution that is 0.300 M C₅H₅N(aq)and 0.500 M C₅H₅NHCl(aq)?

A)8.53
B)5.25
C)8.97
D)5.47
E)5.03

Question 23

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 9? More than one answer may be possible.

Question 24

Calculate the ratio of the molarities of HPO₄^2- and H₂PO₄^- ions required to achieve buffering at pH = 7.00.For H₃PO₄,pK_a1 = 2.12,pK_a2 = 7.21,and pK_a3 = 12.68.

A)0.81
B)1.23
C)0.62
D)0.21
E)1.62

Question 25

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of NaOH are added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

A)4.75
B)4.70
C)4.80
D)4.84
E)4.66

Question 26

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 2.5?

Question 27

A buffer solution contains 0.25 M NaNO₂(aq)and 0.80 M HNO₂(aq)(pK_a = 3.37).What is the pH after 0.10 mol HBr are added to 1.00 L of this buffer?

A)11.41
B)4.15
C)2.59
D)9.85
E)3.37

Question 28

A buffer contains equal concentrations of NH₃(aq)and NH₄Cl(aq).What is the pH of the buffer? (K_b (NH₃)= 1.8 * 10^-5)

A)9.26
B)4.74
C)7.00
D)13.00

Question 29

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 7?

Question 30

For NH₃,pK_b = 4.74.What is the pH of an aqueous buffer solution that is 0.050 M NH₃(aq)and 0.20 M NH₄Cl(aq)?

A)9.86
B)5.34
C)9.26
D)8.66
E)4.14

Question 31

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid,K_a = 1.8 * 10^-5 and for NH₃,K_b = 1.8 * 10^-5.

A)10 mL of 0.1 M NH₃(aq)+ 10 ml of 0.1 M HCl(aq)
B)10 mL of 0.1 M aqueous acetic acid + 5.0 mL of 0.1 M NaOH(aq)
C)10 mL of 0.1 M aqueous acetic acid + 10 mL of 0.1 M NaOH(aq)
D)10 mL of 0.1 M aqueous acetic acid + 10 mL 0f 0.1 M NH₃(aq)
E)10 mL of 0.1 M NH₃(aq)+ 5.0 mL of 0.1 M HCl(aq)

Question 32

A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄.What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^- is 7.21.

A)6.91
B)6.67
C)7.21
D)7.33
E)7.09

Question 33

Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO,K_a = 2.2 * 10^-4 and for NH₃,K_b = 1.8 * 10^-5.

A)10 mL of 0.1 M NH₃(aq)+ 10 mL of 0.1 M HCl(aq)
B)10 mL of 0.1 M HCNO(aq)+ 10 mL 0f 0.1 M NaOH(aq)
C)10 mL of 0.1 M HCNO(aq)+ 5.0 mL of 0.1 M NaOH(aq)
D)10 mL of 0.1 M NH₃(aq)+ 10 ml of 0.1 M HCNO(aq)
E)10 mL of 0.1 M NH₃(aq)+ 5.0 mL of 0.1 M HCl(aq)

Question 34

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 4.

Question 35

If a small amount of a strong acid is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

A)the K_a of HA is changed.
B)the strong acid reacts with A^- to give HA,which is a weak acid.
C)no reaction occurs.
D)the strong acid reacts with HA to give H₂A⁺.
E)the strong acid reacts with A^- to give H₂A⁺.

Question 36

A buffer contains equal concentrations of a weak acid,HA,and its conjugate base,A^-.If the value of K_a for HA is 1.0 * 10^-9,what is the pH of the buffer?

A)13.0
B)5.0
C)7.0
D)1.0
E)9.0

Question 37

If a small amount of a strong base is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

A)the K_a of HA is changed.
B)No reaction occurs.
C)the strong base reacts with A^- to give HA,which is a weak acid.
D)the strong base reacts with HA to give AOH and H⁺.
E)the strong base reacts with HA to give A^- which is a weak base.

Question 38

Calculate the ratio of the molarities of CO₃^2- and HCO₃^- ions required to achieve buffering at pH = 9.0.For H₂CO₃,pK_a1 = 6.37,and pK_a2 = 10.00.

A)0.50
B)3.16
C)1.65
D)0.32
E)0.61

Question 39

For HF,pK_a = 3.45.What is the pH of an aqueous buffer solution that is 0.100 M HF(aq)and 0.300 M KF(aq)?

A)10.07
B)2.97
C)3.45
D)3.93
E)11.03

Question 40

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 10.8.More than one answer may be possible.

Question 41

What is the pH at the stoichiometric point for the titration of 0.26 M CH₃NH₂(aq)with 0.26 M HClO₄(aq)? For CH₃NH₂,K_b = 3.6 * 10^-4.

A)5.72
B)7.00
C)5.57
D)2.16
E)2.01

Question 42

Calculate the equilibrium constant for the reaction that occurs when perchloric acid is added to the buffer B(aq)/BHCl(aq).The K_b of B is 3.4 *10^-5.

Question 43

What is the pH at the half-stoichiometric point for the titration of 0.88 M HNO₂(aq)with 0.10 M KOH(aq)? For HNO₂,K_a = 4.3 * 10^-4.

A)3.37
B)2.01
C)1.86
D)7.00
E)1.71

Question 44

Calculate the equilibrium constant for the reaction that occurs when nitric acid is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 1.2 * 10^-5.

Question 45

What is the concentration of acetate ion at the stoichiometric point in the titration of 0.018 M CH₃COOH(aq)with 0.036 M NaOH(aq)? For acetic acid,K_a = 1.8 * 10^-5.

A)0.018 M
B)0.0090 M
C)0.024 M
D)0.012 M
E)0.036 M

Question 46

What is the pH at the half-stoichiometric point for the titration of 0.22 M HNO₂(aq)with 0.10 M KOH(aq)? For HNO₂,K_a = 4.3 * 10^-4.

A)2.31
B)7.00
C)2.01
D)3.37
E)2.16

Question 47

What is the pH at the stoichiometric point for the titration of 0.100 M CH₃COOH(aq)with 0.100 M KOH(aq)? The value of K_a for acetic acid is 1.8 * 10^-5.

A)5.28
B)8.72
C)7.00
D)9.26
E)8.89

Question 48

What is the concentration of acetate ion at the stoichiometric point in the titration of 0.018 M CH₃COOH(aq)with 0.072 M NaOH(aq)? For acetic acid,K_a = 1.8 * 10^-5.

A)0.054 M
B)0.036 M
C)0.018 M
D)0.072 M
E)0.014 M

Question 49

Which of the following indicators would be most suitable for the titration of 0.10 M (CH₃)₃N(aq)with 0.10 M HClO₄(aq)? For trimethyamine,pK_b = 4.19.

A)Bromothymol blue (pK_In = 7.1)
B)Alizarin yellow (pK_In = 11.2)
C)Bromocresol green (pK_In = 4.7)
D)Tthymol blue (pK_In = 1.7)
E)Phenolphthalein (pK_In = 9.4)

Question 50

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 4.1 *10^-5.

Question 51

Which of the following indicators would be most suitable for the titration of 0.10 M lactic acid with 0.10 M KOH(aq)? For lactic acid,pK_a = 3.08.

A)Methyl orange (pK_In = 3.4)
B)Thymol blue (pK_In = 1.7)
C)Alizarin yellow (pK_In = 11.2)
D)Bromophenol blue (pK_In = 3.9)
E)Phenol red (pK_In = 7.9)

Question 52

At the stoichiometric point in the titration of 0.260 M CH₃NH₂(aq)with 0.260 M HCl(aq),

A)the pH is less than 7.
B)[CH₃NH₃⁺] = 0.260 M.
C)the pH is 7.0.
D)[CH₃NH₂] = 0.130 M.
E)the pH is greater than 7.

Question 53

At the stoichiometric point in the titration of 0.130 M HCOOH(aq)with 0.130 M KOH(aq),

A)the pH is 7.0.
B)[HCOOH] = 0.0650 M.
C)[HCO₂-] = 0.130 M.
D)the pH is greater than 7.
E)the pH is less than 7.

Question 54

For the titration of 50.0 mL of 0.020 M aqueous salicylic acid with 0.020 M KOH(aq),calculate the pH after the addition of 55.0 mL of KOH(aq).For salycylic acid,pK_a = 2.97.

A)10.98
B)7.00
C)11.26
D)12.02
E)12.30

Question 55

The curve for the titration of 50.0 mL of 0.0200 M C₆H₅COOH(aq)with 0.100 M NaOH(aq)is given below.What are the main species in the solution after 7.5 mL of base have been added?

Question 56

The titration curve for the titration of 0.100 M H₂SO₃(aq)with 0.100 M KOH(aq)is given below. Estimate pK_a1 and pK_a2 of H₂SO₃.

Question 57

Consider the titration of 10.0 mL of 0.100 M (CH₃)₃N(aq)with 0.100 M HClO₄(aq).What is the formula of the main species in the solution after the addition of 10.0 mL of acid?

Question 58

Consider the titration of 50.0 mL of 0.0200 M HClO(aq)with 0.100 M NaOH(aq).What is the formula of the main species in the solution after the addition of 10.0 mL of base?

Question 59

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer B(aq)/BHCl(aq).The K_b of B is 1.5 * 10^-5.

Question 60

Consider the titration of 50.0 mL of 0.0200 M C₆H₅COOH(aq),with 0.100 M NaOH(aq).What is the formula of the main species in the solution after the addition of 10.0 mL of base? Do not consider spectator ions.

Question 61

The titration curve for the titration of 0.100 M H₂SO₃(aq)with 0.100 M KOH(aq)is given below.
The major species in solution after 75 mL of KOH(aq)has been added are

A)HSO₃^-(aq)and Na⁺(aq).
B)SO₃^2-(aq),and Na⁺(aq).
C)SO₃^2-(aq),OH^-(aq),and Na⁺(aq).
D)H₂SO₃(aq),HSO₃^-,and Na⁺(aq).
E)HSO₃^-(aq),SO₃^2-(aq),and Na⁺(aq).

Question 62

Calculate the value of the equilibrium constant for the reaction AgCl(s)+ 2NH₃(aq) →Ag(NH₃)₂+(aq)+ Cl^-(aq)
Given K_sp = 1.6 * 10^-10 for silver chloride and K_f = 1.6 * 10⁷ for the ammonia complex of Ag⁺ ions,Ag(NH₃)²⁺.

A)1.0 * 10^-17
B)6.3 * 10⁹
C)6.3 * 10^-8
D)1.0 * 10¹⁷
E)2.6 * 10^-3

Question 63

A certain weak acid has a K_a of 2.0 * 10^-5.What is the equilibrium constant for the reaction of this acid with a strong base?

Question 64

The titration curve for the titration of 0.100 M Na₂CO₃(aq)with 0.100 M HClO₄(aq)is:
The main species in the solution after the addition of 35 mL of HClO₄ are

A)HCO₃^-,H₂CO₃,Na⁺,and ClO₄^-.
B)H₂CO₃,Na⁺,and ClO₄^-.
C)CO₃^2-,HCO₃,Na⁺,and ClO₄^-.
D)CO₃^2-,Na⁺,and ClO₄^-.
E)HCO₃^-,Na⁺,and ClO₄^-.

Question 65

Consider the titration of 15.0 mL of 0.200 M H₃PO₄(aq)with 0.200 M NaOH(aq).What is(are)the major species in solution after the addition of 30.0 mL of base?

A)HPO₄^2-(aq)
B)H₂PO₄^-(aq)
C)H₂PO₄^-(aq)and HPO₄^2-(aq)
D)H₃PO₄(aq)and H₂PO₄^-(aq)
E)PO₄^3-(aq)

Question 66

Calculate the solubility product of calcium hydroxide given that the solubility of Ca(OH)₂(s)in water at 25 ^$\circ$ C is 0.011 M.

A)1.5 * 10^-8
B)1.1 * 10^-5
C)2.7 * 10^-6
D)5.3 * 10^-6
E)1.2 * 10^-4

Question 67

You have available the following reagents as 0.10 M aqueous solutions: NaOH,HCl,HCN (pK_a = 9.31),aniline (pK_b = 9.13),HNO₂ (pK_a = 3.25),and CH₃NH₂ (pK_b = 3.34).Which two reagents would you use to make a buffer with a pH of 10.6?

A)NaOH and HCN
B)HCl and aniline
C)HCl and CH₃NH₂
D)NaOH and HNO₂

Question 68

The titration curve for the titration of 0.100 M Na₂CO₃(aq)with 0.100 M HClO₄(aq)is: Estimate pK_b1.

A)8.5
B)6.4
C)3.7
D)10.3
E)7.6

Question 69

Silver bromide is most soluble in

A)pure H₂O(l).
B)dilute HNO₃(aq).
C)0.10 M AgNO₃(aq).
D)dilute NH₃(aq).
E)0.10 M NaCl(aq).

Question 70

If equal volumes of 0.004 M Pb(NO₃)₂(aq)and 0.004 M KI(aq)are mixed,what reaction,if any,occurs? The value of K_sp for PbI₂ is 1.4 * 10^-8.

A)The solution turns purple because of formation of I₂.
B)PbI₂(s)precipitates.
C)KNO₃(s)precipitates.
D)No reaction occurs.
E)The value of K_sp changes to 9 * 10^-9.

Question 71

The Cu²⁺ ion can be separated from Ag⁺,Ca²⁺,and K⁺ in aqueous solution by

A)precipitation of Cu²⁺ as CuS(s)at pH-1.
B)precipitation of Cu²⁺ as Cu(OH)₂(s)with 6 M NaOH(aq).
C)precipitation of Cu²⁺ as CuCl₂(s)with 6 M HCl(aq).
D)precipitation of Ag⁺,Ca²⁺,and K⁺ as the carbonates.
E)None of these procedures will separate Cu²⁺ from the other ions.

Question 72

The titration curve for the titration of 0.100 M Na₂CO₃(aq)with 0.100 M HClO₄(aq)is: Estimate pK_b2.

A)7.6
B)10.3
C)6.4
D)8.5
E)3.7

Question 73

Which of the following water-insoluble salts is more soluble in 1.0 M HClO₄(aq)?

A)AgBr
B)PbF₂
C)Hg₂Br₂
D)PbI₂
E)AgClO₄

Question 74

If you wish to increase the solubility of silver benzoate,a preservative,you would

A)add sodium hydroxide.
B)decrease the pH.
C)add sodium acetate.
D)add sodium benzoate.
E)add silver nitrate.

Question 75

What is the relationship between the solubility in water,s,and K_sp for the ionic solid Ca₃(PO₄)₂?

A)K_sp = 72s⁵
B)K_sp = 5s
C)K_sp = 6s²
D)K_sp = s⁵

Question 76

What is the equilibrium constant for the titration reaction involving HClO₄(aq)and Ba(OH)₂(aq)?

A)1.0 * 10¹⁴
B)2.0 * 10¹⁴
C)1.0 * 10⁷
D)1.0 * 10^-14

Question 77

If the molar solubility of the compound M₂A₃ is 7.0 * 10^-6 M,what is the K_sp for this compound?

A)1.7 * 10^-26
B)1.8 * 10^-24
C)2.9 * 10^-10
D)3.5 * 10^-5

Question 78

Consider the titration of 15.0 mL of 0.200 M H₃PO₄(aq)with 0.200 M NaOH(aq).What is/are the major species in solution after the addition of 30.0 mL of base?

A)OH^-(aq)
B)H₃PO₄(aq)and H₂PO₄^-(aq)
C)HPO₄^2-(aq)
D)PO₄^3-(aq)

Question 79

What is the main factor that determines the pH of any buffer?

Question 80

What is the equilibrium constant for the titration reaction involving CH₃NH₂(aq)and HBr(aq)?

A)1.0 * 10¹⁴
B)2.8 * 10³
C)2.8 * 10^-11
D)3.6 * 10¹⁰