Deck 13: Aqueous Equilibria

Question 1

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

Answer 1

5.46

Question 2

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.True or false?

Answer 2

False

Question 3

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

Answer 3

9.61

Question 4

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

Question 5

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

Question 6

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 7

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.True or false?

Question 8

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 9

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 10

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 11

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.True or false?

Question 12

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 13

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 14

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 15

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 16

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

Question 17

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 18

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 19

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 20

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.True or false?

Question 21

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 22

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 23

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 24

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 25

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 26

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 27

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 28

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 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

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 31

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 32

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 33

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 34

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 35

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 36

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 37

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 38

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 39

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 40

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 41

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 42

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 43

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 44

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 45

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 46

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 47

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 48

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 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

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 51

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 52

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 53

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 54

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 55

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 56

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 57

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 58

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 59

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 60

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 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

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 63

Calculate the solubility product of calcium hydroxide given that the solubility of Ca(OH)₂(s)in water at 25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 64

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

Question 66

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 67

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 68

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 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

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 71

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

Question 72

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 73

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

Question 74

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 75

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 76

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 77

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 78

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 79

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 80

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.