Deck 15: Acid-Base Equilibria

Question 1

You have a 250.-mL sample of 1.28 M acetic acid (K_a = 1.8 $\times$ 10^-5).Calculate the pH of the best buffer.

A)7.00
B)4.74
C)4.25
D)9.26
E)none of these

Answer 1

4.74

Question 2

Which of the following will not produce a buffered solution?

A)100 mL of 0.1 M Na₂CO₃ and 50 mL of 0.1 M HCl
B)100 mL of 0.1 M NaHCO₃ and 25 mL of 0.2 M HCl
C)100 mL of 0.1 M Na₂CO₃ and 75 mL of 0.2 M HCl
D)50 mL of 0.2 M Na₂CO₃ and 5 mL of 1.0 M HCl
E)100 mL of 0.1 M Na₂CO₃ and 50 mL of 0.1 M NaOH

Answer 2

100 mL of 0.1 M Na₂CO₃ and 50 mL of 0.1 M NaOH

Question 3

Which of the following is true for a buffered solution?

A)The solution resists change in its [H⁺].
B)The solution will not change its pH very much even if a concentrated acid is added.
C)The solution will not change its pH very much even if a strong base is added.
D)Any H⁺ ions will react with a conjugate base of a weak acid already in solution.
E)All of these.

Answer 3

All of these.

Question 4

The following question refers to a 2.0-liter buffered solution created from 0.31 M NH₃ (K_b = 1.8 $\times$ 10^-5)and 0.26 M NH₄F.When 0.10 mol of H⁺ ions is added to the solution what is the pH?

A)4.82
B)4.66
C)10.53
D)9.18
E)7.88

Question 5

A 100.mL sample of 0.10 M HCl is mixed with 50.mL of 0.11 M NH₃.What is the resulting pH? (K_b for NH₃ = 1.8 $\times$ 10^-5)

A)3.09
B)10.91
C)12.48
D)1.35
E)1.52

Question 6

You have a 250.0-mL sample of 1.00 M acetic acid (K_a = 1.8 $\times$ 10^-5).Calculate the pH after adding 0.0050 mol of NaOH to 1.0 liter of the best buffer.

A)7.05
B)2.41
C)3.54
D)4.78
E)none of these

Question 7

Suppose a buffer solution is made from formic and (HCHO₂)and sodium formate (NaCHO₂).What is the net ionic equation for the reaction that occurs when a small amount of hydrochloric acid is added to the buffer?

A)H₃O⁺(aq)+ OH^-(aq) $\to$ 2H₂O(l)
B)H₃O⁺(aq)+ HCHO₂(aq) $\to$ H₂O(l)+ H₂CHO₂⁺(aq)
C)HCl(aq)+ OH^-(aq) $\to$ H₂O(l)+ Cl^-(aq)
D)HCl(aq)+ CHO₂^-(aq) $\to$ HCHO₂(aq)+ Cl^-(aq)
E)H₃O⁺(aq)+ CHO₂^-(aq) $\to$ HCHO₂(aq)+ H₂O(l)

Question 8

A weak acid,HF,is in solution with dissolved sodium fluoride,NaF.If HCl is added,which ion will react with the extra hydrogen ions from the HCl to keep the pH from changing?

A)OH^-
B)Na⁺
C)F^-
D)Na^-
E)none of these

Question 9

What will happen if a small amount of hydrochloric acid is added to a 0.1 M solution of HF?

A)The percent ionization of HF will increase.
B)The percent ionization of HF will decrease.
C)The percent ionization of HF will remain unchanged.
D)K_a for HF will increase.
E)K_a for HF will decrease.

Question 10

Which of the following mixtures would result in a buffered solution?

A)Mixing 100.0 mL of 0.100 M HCl with 100.0 mL of 0.100 M NaOH.
B)Mixing 100.0 mL of 0.100 M NH₃ (K_b = 1.8 $\times$ 10^-5)with 100.0 mL of 0.100 M NaOH.
C)Mixing 100.0 mL of 0.100 M HCl with 100.0 mL of 0.100 M NH₃ (K_b = 1.8 $\times$ 10^-5).
D)Mixing 50.0 mL of 0.100 M HCl with 100.0 mL of 0.100 M NH₃ (K_b = 1.8 $\times$ 10^-5).
E)At least two of the above mixtures would result in a buffered solution.

Question 11

For a solution equimolar in HCN and NaCN,which statement is false?

A)This is an example of the common ion effect.
B)The [H⁺] is larger than it would be if only the HCN was in solution.
C)The [H⁺] is equal to the K_a.
D)Addition of more NaCN will shift the acid dissociation equilibrium of HCN to the left.
E)Addition of NaOH will increase [CN^-] and decrease [HCN].

Question 12

The following question refers to a 2.0-liter buffered solution created from 0.72 M NH₃ (K_b = 1.8 $\times$ 10^-5)and 0.26 M NH₄F.What is the pH of this solution?

A)9.26
B)9.70
C)4.30
D)5.18
E)8.81

Question 13

You have solutions of 0.200 M HNO₂ and 0.200 M KNO₂ (K_a for HNO₂ = 4.00 $\times$ 10^-4).A buffer of pH 3.000 is needed.What volumes of HNO₂ and KNO₂ are required to make 1 liter of buffered solution?

A)500 mL of each
B)286 mL HNO₂;714 mL KNO₂
C)413 mL HNO₂;587 mL KNO₂
D)714 mL HNO₂;286 mL KNO₂
E)587 mL HNO₂;413 mL KNO₂

Question 14

You have a 250.-mL sample of 1.250 M acetic acid (K_a = 1.8 $\times$ 10^-5).Assuming no volume change,how much NaOH must be added to make the best buffer?

A)6.25 g
B)12.5 g
C)16.3 g
D)21.3 g
E)none of these

Question 15

You have a 250.0-mL sample of 1.00 M acetic acid (K_a = 1.8 $\times$ 10^-5).Calculate the pH after adding 0.0040 mol HCl to 1.0 liter of the best buffer.

A)4.72
B)2.35
C)3.12
D)6.98
E)none of these

Question 16

Suppose a buffer solution is made from formic acid,HCHO₂,and sodium formate,NaCHO₂.What is the net ionic equation for the reaction that occurs when a small amount of sodium hydroxide is added to the buffer?

A)NaOH(aq)+ H₃O⁺(aq) $\to$ Na⁺(aq)+ 2H₂O(l)
B)H₃O⁺(aq)+ OH^-(aq) $\to$ 2H₂O(l)
C)OH^-(aq)+ HCHO₂(aq) $\to$ CHO₂^-(aq)+ H₂O(l)
D)NaOH(aq)+ HCHO₂(aq) $\to$ NaCHO₂(aq)+ H₂O(l)
E)Na⁺(aq)+ HCHO₂(aq) $\to$ NaH(aq)+ HCO₂⁺(aq)

Question 17

What will happen if a small amount of sodium hydroxide is added to a 0.1 M solution of ammonia?

A)K_b for ammonia will increase.
B)K_b for ammonia will decrease.
C)The percent ionization of ammonia will increase.
D)The percent ionization of ammonia will decrease.
E)The percent ionization of ammonia will remain unchanged.

Question 18

What combination of substances will give a buffered solution that has a pH of 5.05? (Assume each pair of substances is dissolved in 5.0 L of water. )(K_b for NH₃ = 1.8 $\times$ 10^-5;K_b for C₅H₅N = 1.7 $\times$ 10^-9)

A)1.0 mole NH₃ and 1.5 mole NH₄Cl
B)1.5 mole NH₃ and 1.0 mole NH₄Cl
C)1.0 mole C₅H₅N and 1.5 mole C₅H₅NHCl
D)1.5 mole C₅H₅N and 1.0 mole C₅H₅NHCl
E)none of these

Question 19

What is the percent dissociation of HNO₂ when 0.064 g of sodium nitrite is added to 120.0 mL of a 0.057 M HNO₂ solution? K_a for HNO₂ is 4.0 $\times$ 10^-4.

A)13%
B)0.30%
C)5.2%
D)0.075%
E)8.4%

Question 20

Calculate the [H⁺] in a solution that is 0.16 M in NaF and 0.25 M in HF.(K_a = 7.2 $\times$ 10^-4)

A)7.2 $\times$ 10^-4 M
B)1.6 M
C)1.1 $\times$ 10^-3 M
D)0.20 M
E)4.6 $\times$ 10^-4 M

Question 21

Calculate the pH of a solution made by mixing 100.0 mL of 0.635 M NH₃ with 100.0 mL of 0.100 M HCl.(K_b for NH₃ = 1.8 $\times$ 10^-5)

A)9.98
B)4.02
C)8.53
D)9.26
E)none of these

Question 22

The following question refers to the following system: A 1.0-liter solution contains 0.25 M HF and 0.32 M NaF (K_a for HF is 7.2 $\times$ 10^-4). If one adds 0.30 liters of 0.020 M KOH to the solution,what will be the change in pH?

A)0.02
B)3.27
C)0.13
D)-0.11
E)-0.28

Question 23

You have two buffered solutions.Buffered solution 1 consists of 5.0 M HOAc and 5.0 M NaOAc;buffered solution 2 is made of 0.050 M HOAc and 0.050 M NaOAc.
How do the pHs of the buffered solutions compare?

A)The pH of buffered solution 1 is greater than that of buffered solution 2.
B)The pH of buffered solution 2 is greater than that of buffered solution 1.
C)The pH of buffered solution 1 is equal to that of buffered solution 2.
D)Cannot be determined without the K_a values.
E)None of these (A-D).

Question 24

Consider a solution consisting of the following two buffer systems: H₂CO₃ HCO₃^- + H⁺ pK_a = 6.4
H₂PO₄^- HPO₄^2- + H⁺ pK_a = 7.2
At pH 6.4,which one of the following is true of the relative amounts of acid and conjugate base present?

A)[H₂CO₃] > [HCO₃^-] and [H₂PO₄^-] > [HPO₄^2-]
B)[H₂CO₃] = [HCO₃^-] and [H₂PO₄^-] > [HPO₄^2-]
C)[H₂CO₃] = [HCO₃^-] and [HPO₄^2-] > [H₂PO₄^-]
D)[HCO₃^-] > [H₂CO₃] and [HPO₄^2-] > [H₂PO₄^-]
E)[H₂CO₃] > [HCO₃^-] and [HPO₄^2-] > [H₂PO₄^-]

Question 25

You are given 5.00 mL of an H₂SO₄ solution of unknown concentration.You divide the 5.00-mL sample into five 1.00-mL samples and titrate each separately with 0.1000 M NaOH.In each titration the H₂SO₄ is completely neutralized.The average volume of NaOH solution used to reach the endpoint is 15.6 mL.What was the concentration of H₂SO₄ in the 5.00-mL sample?

A)1.56 M
B)3.90 M
C)0.780 M
D)0.156 M
E)7.80 M

Question 26

Calculate the pH of a solution that is 2.00 M HF,1.00 M NaOH,and 0.642 M NaF.(K_a = 7.2 $\times$ 10^-4)

A)3.14
B)3.36
C)2.65
D)2.93
E)none of these

Question 27

In titrating 0.20 M hydrochloric acid,HCl,with 0.20 M NaOH at 25°C,the solution at the equivalence point is

A)0.20 M NaCl
B)very acidic
C)slightly acidic
D)0.10 M HCl and 0.20 M NaOH
E)0.10 M NaCl

Question 28

Which of the following solutions will be the best buffer at a pH of 9.26? (K_a for HC₂H₃O₂ is 1.8 $\times$ 10^-5,K_b for NH₃ is 1.8 $\times$ 10^-5).

A)0.10 M HC₂H₃O₂ and 0.10 M Na C₂H₃O₂
B)5.0 M HC₂H₃O₂ and 5.0 M Na C₂H₃O₂
C)0.10 M NH₃ and 0.10 M NH₄Cl
D)5.0 M NH₃ and 5.0 M NH₄Cl
E)5.0 M HC₂H₃O₂ and 5.0 M NH₃

Question 29

A solution contains 0.250 M HA (K_a = 1.0 $\times$ 10^-6)and 0.45 M NaA.What is the pH after 0.17 mole of HCl is added to 1.00 L of this solution?

A)0.77
B)7.82
C)5.82
D)1.97
E)8.18

Question 30

Given 100.0 mL of a buffer that is 0.50 M in HOCl and 0.77 M in NaOCl,what is the pH after 10.0 mL of 1.0 M NaOH has been added? (K_a for HOCl = 3.5 $\times$ 10^-8)

A)7.68
B)7.74
C)7.46
D)7.12
E)7.79

Question 31

How many moles of HCl need to be added to 150.0 mL of 0.50 M NaZ to have a solution with a pH of 6.50? (K_a of HZ is 2.3 $\times$ 10^-5)? Assume negligible volume of the HCl.

A)6.8 $\times$ 10^-3
B)7.5 $\times$ 10^-2
C)5.0 $\times$ 10^-1
D)1.0 $\times$ 10^-3
E)none of these

Question 32

How many moles of solid NaF would have to be added to 1.0 L of 2.39 M HF solution to achieve a buffer of pH 3.35? Assume there is no volume change.(K_a for HF = 7.2 $\times$ 10^-4)

A)3.9
B)0.50
C)0.67
D)1.0
E)1.6

Question 33

Calculate the pH of a solution that is 0.50 M in HF (K_a = 7.2 $\times$ 10^-4)and 0.95 M in NaF.

A)3.14
B)3.42
C)0.28
D)10.58
E)2.86

Question 34

The following question refers to the following system: A 1.0-liter solution contains 0.25 M HF and 0.83 M NaF (K_a for HF is 7.2 $\times$ 10^-4). What is the pH of this solution?

A)3.14
B)3.66
C)2.62
D)0.52
E)10.34

Question 35

Consider a solution of 2.0 M HCN and 1.0 M NaCN (K_a for HCN = 6.2 $\times$ 10^-10).Which of the following statements is true?

A)The solution is not a buffer because [HCN] is not equal to [CN^-].
B)The pH will be below 7.00 because the concentration of the acid is greater than that of the base.
C)[OH^-] > [H⁺]
D)The buffer will be more resistant to pH changes from addition of strong acid than of strong base.
E)All of the above are false.

Question 36

How many mmoles of HCl must be added to 100 mL of a 0.100 M solution of methylamine (pK_b = 3.36)to give a buffer having a pH of 10.00?

A)8.1
B)18.7
C)20.0
D)41.5
E)12.7

Question 37

Buffered solution 1 has a greater buffering capacity than buffered solution 2.

Question 38

A solution contains 0.500 M HA (K_a = 1.0 $\times$ 10^-8)and 0.432 M NaA.What is the [H⁺] after 0.10 mole of HCl is added to 1.00 L of this solution?

A)1.0 $\times$ 10^-8 M
B)3.0 $\times$ 10^-8 M
C)5.5 $\times$ 10²¹ M
D)1.8 $\times$ 10^-8 M
E)none of these

Question 39

What is the pH of a solution that results when 0.010 mol HNO₃ is added to 500.mL of a solution that is 0.10 M in aqueous ammonia and 0.55 M in ammonium nitrate.Assume no volume change.(The K_b for NH₃ = 1.8 $\times$ 10^-5. )

A)9.26
B)5.05
C)10.11
D)8.40
E)8.71

Question 40

One milliliter (1.00 mL)of acid taken from a lead storage battery is pipetted into a flask.Water and phenolphthalein indicator are added,and the solution is titrated with 0.55 M NaOH until a pink color appears;12.0 mL are required.The number of grams of H₂SO₄ (formula weight = 98)present in one liter of the battery acid is:

A)647
B)323
C)30
D)1294
E)54

Question 41

A 50.00-mL sample of 0.100 M KOH is titrated with 0.202 M HNO₃.Calculate the pH of the solution after 52.00 mL of HNO₃ is added.

A)12.73
B)0.99
C)1.27
D)13.01
E)none of these

Question 42

Consider the following information about the diprotic acid,ascorbic acid.(H₂As for short,molar mass 176.1)
H₂As HAs^- + H⁺ pK_a
= 4.10 (K_a
= 7.9 $\times$ 10^-5)
HAs^- As^2- + H⁺ pK_a
= 11.79 (K_a
= 1.6 $\times$ 10^-12)
The titration curve for disodium ascorbate,Na₂As,with standard HCl is shown below:

-What major species is (are)present at point III?

A)As^2- and HAs^-
B)HAs^- only
C)HAs^- and H₂As
D)H₂As only
E)H₂As and H⁺

Question 43

A solution of hydrochloric acid of unknown concentration was titrated with 0.23 M NaOH.If a 100.-mL sample of the HCl solution required exactly 10.mL of the NaOH solution to reach the equivalence point,what was the pH of the HCl solution?

A)12.4
B)1.6
C)-0.4
D)3.3
E)6.6

Question 44

A titration of 200.0 mL of 1.00 M H₂A was done with 1.38 M NaOH.For the diprotic acid H₂A,K_a1 = 2.5 $\times$ 10^-5,K_a2 = 3.1 $\times$ 10^-9.Calculate the pH after 100.0 mL of 1.38 M NaOH have been added.

A)9.05
B)8.86
C)5.14
D)9.90
E)4.95

Question 45

A titration of 200.0 mL of 1.00 M H₂A was done with 1.02 M NaOH.For the diprotic acid H₂A,K_a1 = 2.5 $\times$ 10^-5,K_a2 = 3.1 $\times$ 10^-9.Calculate the pH after 600.0 mL of 1.02 M NaOH have been added.

A)13.423
B)0.577
C)13.712
D)0.288
E)9.423

Question 46

A 75.0-mL sample of 0.0500 M HCN (K_a = 6.2 $\times$ 10^-10)is titrated with 0.277 M NaOH.What is the [H⁺] in the solution after 3.0 mL of 0.277 M NaOH have been added?

A)4.6 $\times$ 10^-6 M
B)1.0 $\times$ 10^-7 M
C)3.5 M
D)2.2 $\times$ 10^-9 M
E)none of these

Question 47

A student titrates an unknown weak acid,HA,to a pale pink phenolphthalein endpoint with 25.0 mL of 0.100 M NaOH.The student then adds 13.0 mL of 0.100 M HCl.The pH of the resulting solution is 4.7.Which of the following is true?

A)At pH 4.7,half the conjugate base,A^-,has been converted to HA.
B)The pK_a of the acid is 4.7.
C)The pK_a of the acid is less than 4.7.
D)The pK_a of the acid is greater than 4.7.
E)More than one of the above is correct.

Question 48

A 50.0-mL sample of 0.10 M HNO₂ (K_a = 4.0 $\times$ 10^-4)is titrated with 0.12 M NaOH.The pH after 25.0 mL of NaOH have been added is

A)10.43
B)7.00
C)6.57
D)3.57
E)none of these

Question 49

A 100.0-mL sample of 0.503 M H₂A (diprotic acid)is titrated with 0.200 M NaOH.After 125.0 mL of 0.200 M NaOH has been added,the pH of the solution is 4.50.Calculate K_a1 for H₂A.

A)3.2 $\times$ 10^-10
B)4.5
C)3.1 $\times$ 10^-5
D)not enough information to calculate
E)none of these

Question 50

What quantity of NaOH(s)must be added to 2.00 L of 0.434 M HCl to achieve a pH of 13.00? (Assume no volume change. )

A)0.67 mol
B)1.07 mol
C)0.20 mol
D)1.00 $\times$ 10^-13 mol
E)none of these

Question 51

The pH at the equivalence point of the titration of a strong acid with a strong base is:

A)3.9
B)4.5
C)7.0
D)8.2
E)none of these

Question 52

Consider the titration of 300.0 mL of 0.450 M NH₃ (K_b = 1.8 $\times$ 10^-5)with 0.450 M HNO₃.How many milliliters of 0.450 M HNO₃ are required to reach the stoichiometric point of the reaction?

A)3.50 $\times$ 10² mL
B)4.00 $\times$ 10² mL
C)4.50 $\times$ 10² mL
D)3.00 $\times$ 10² mL
E)none of these

Question 53

A 19.0-mL sample of tartaric acid is titrated to a phenolphthalein endpoint with 20.mL of 1.0 M NaOH.Assuming tartaric acid is diprotic,what is the molarity of the acid?

A)1.0 M
B)0.53 M
C)2.0 M
D)1.05 M
E)impossible to determine

Question 54

A titration of 200.0 mL of 1.32 M H₂A was done with 1.00 M NaOH.For the diprotic acid H₂A,K_a1 = 2.5 $\times$ 10^-5,K_a2 = 3.1 $\times$ 10^-9.Calculate the pH before any 1.00 M NaOH has been added.

A)11.76
B)4.48
C)9.52
D)8.96
E)2.24

Question 55

Consider the titration of 300.0 mL of 0.450 M NH₃ (K_b = 1.8 $\times$ 10^-5)with 0.450 M HNO₃.At the stoichiometric point of this titration,the pH is:

A)4.80
B)2.70
C)4.95
D)4.74
E)7.00

Question 56

Consider the titration of 500.0 mL of 0.200 M NaOH with 0.800 M HCl.How many milliliters of 0.800 M HCl must be added to reach a pH of 13.000?

A)55.6 mL
B)24.6 mL
C)18.5 mL
D)12.9 mL
E)4.32 mL

Question 57

Consider the titration of 300.0 mL of 0.577 M NH₃ (K_b = 1.8 $\times$ 10^-5)with 0.500 M HNO₃.After 150.0 mL of 0.500 M HNO₃ have been added,the pH of the solution is:

A)4.63
B)11.37
C)6.37
D)9.37
E)none of these

Question 58

What is the molarity of a sodium hydroxide solution if 28.7 mL of this solution reacts exactly with 22.30 mL of 0.253 M sulfuric acid?

A)0.197 M
B)0.786 M
C)7.26 M
D)0.393 M
E)0.221 M

Question 59

If 25 mL of 0.750 M HCl are added to 100.mL of 0.352 M NaOH,what is the final pH?

A)13.12
B)0.88
C)13.45
D)0.55
E)7.00

Question 60

If 25.0 mL of 0.451 M NaOH solution is titrated with 0.253 M H₂SO₄,the flask at the endpoint will contain (besides the indicator phenolphthalein)as the principal components:

A)sodium hydroxide,sulfuric acid,and water
B)dissolved sodium sulfate and water
C)sodium hydroxide,sodium sulfate,and water
D)dissolved sodium sulfate,sulfuric acid,and water
E)precipitated sodium sulfate and water

Question 61

A solution contains 10.mmol of H₃PO₄ and 5.0 mmol of NaH₂PO₄.How many milliliters of 0.10 M NaOH must be added to reach the second equivalence point of the titration of the H₃PO₄ with NaOH?

A)250
B)150
C)1.0 $\times$ 10²
D)50
E)2.0 $\times$ 10²

Question 62

A solution containing 10.mmol of and 5.0 mmol of is titrated with 1.7 M HCl.What total volume of HCl must be added to reach the second equivalence point?

A)8.8 mL
B)5.9 mL
C)2.9 mL
D)14.7 mL
E)19.7 mL

Question 63

You have 100.0 mL of 0.100 M aqueous solutions of each of the following acids: HCN,HF,HCl,and HC₂H₃O₂.You titrate each with 0.100 M NaOH (aq).Rank the pHs of each of the solutions when each are titrated to the equivalence point,from highest to lowest pH. K_a for HCN = 6.2 $\times$ 10^-10
K_a for HF = 7.2 $\times$ 10^-4
K_a for HC₂H₃O₂ = 1.8 $\times$ 10^-5

A)HCN,HC₂H₃O₂,HF,HCl
B)HCl,HF,HCN,HC₂H₃O₂
C)HF,HCN,HC₂H₃O₂,HCl
D)HC₂H₃O₂,HCl,HCN,HF
E)none of these

Question 64

A 50.00-mL solution of 0.0350 M hydrocyanic acid (K_a = 6.2 $\times$ 10^-10)is titrated with a 0.0333 M solution of sodium hydroxide as the titrant.What is the pH of the acid solution after 15.00 mL of titrant have been added? (K_w = 1.00 $\times$ 10^-14)

A)1.46
B)5.33
C)8.81
D)10.60
E)9.21

Question 65

A 100.0-mL sample of 0.2 M (CH₃)₃N (K_b = 5.33 $\times$ 10^-5)is titrated with 0.2 M HCl.What is the pH at the equivalence point?

A)2.6
B)8.6
C)10.7
D)5.4
E)7.0

Question 66

How many of the following will raise the pH of a weak acid HA in aqueous solution?
I.addition of water
II.making a buffered solution by adding NaA(s)
III.addition of NaCl(s)
IV.addition of HNO₃
V.titrating with KOH

A)1
B)2
C)3
D)4
E)5

Question 67

Consider the following information about the diprotic acid,ascorbic acid.(H₂As for short,molar mass 176.1)
H₂As HAs^- + H⁺ pK_a
= 4.10 (K_a
= 7.9 $\times$ 10^-5)
HAs^- As^2- + H⁺ pK_a
= 11.79 (K_a
= 1.6 $\times$ 10^-12)
The titration curve for disodium ascorbate,Na₂As,with standard HCl is shown below:

-What is the pH at point III?

A)4.10
B)7.95
C)11.79
D)12.39
E)none of these

Question 68

Consider the following information about the diprotic acid,ascorbic acid.(H₂As for short,molar mass 176.1)
H₂As HAs^- + H⁺ pK_a
= 4.10 (K_a
= 7.9 $\times$ 10^-5)
HAs^- As^2- + H⁺ pK_a
= 11.79 (K_a
= 1.6 $\times$ 10^-12)
The titration curve for disodium ascorbate,Na₂As,with standard HCl is shown below:

-What is the pH at point I (V₁/2 HCl added)?

A)4.10
B)7.95
C)11.79
D)12.39
E)none of these

Question 69

Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine,C₂H₅NH₂,by 1.0 M perchloric acid,HClO₄.(pK_b for C₂H₅NH₂ = 3.25)

A)6.05
B)2.24
C)5.53
D)2.09
E)5.38

Question 70

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 $\times$ 10^-10)with 0.500 M HCl.For calculating the volume of HCl required to reach a pH of 8.0,which of the following expressions is correct? (x = volume in mL of HCl required to reach a pH of 8.0)

A) = [aniline]
B)[H⁺] = x
C) = [aniline]
D) = [aniline]
E)none of these

Question 71

What volume of 0.0100 M NaOH must be added to 1.00 L of 0.0500 M HOCl to achieve a pH of 8.00? The K_a for HOCl is 3.5 $\times$ 10^-8.

A)1.0 L
B)5.0 L
C)1.2 L
D)3.9 L
E)none of these

Question 72

You dissolve 1.15 grams of an unknown diprotic acid in 200.0 mL of H₂O.This solution is just neutralized by 5.00 mL of a 1.00 M NaOH solution.What is the molar mass of the unknown acid?

A)230
B)115
C)28.8
D)460
E)none of these

Question 73

Which of the following is a major species present at point IV?

A)H₂As
B)HAs^-
C)As^2-
D)H⁺
E)none of these

Question 74

A 2.36-g sample of an acid,H₂X,requires 45.0 mL of a 0.500 M NaOH solution for complete reaction (removing both protons).The molar mass of the acid is:

A)105
B)255
C)232
D)210
E)none of these

Question 75

A 25.00-mL sample of propanoic acid,CH₃CH₂COOH,of unknown concentration was titrated with 0.111 M KOH.The equivalence point was reached when 44.54 mL of base had been added.What is the concentration of the propanoate ion at the equivalence point?

A)0.111 M
B)0.0711 M
C)0.198 M
D)0.128 M
E)0.147 M

Question 76

Which of the following is the net ionic equation for the reaction that occurs during the titration of nitric acid with potassium hydroxide?

A)HNO₃ + K⁺ OH^- $\to$ KNO₃ + H₂O
B)HNO₃ + H₂O $\to$ NO3^- + H₃O⁺
C)HNO₃ + KOH $\to$ K⁺ + NO₃^- + H₂O
D)HNO₃ + OH^- $\to$ NO₃^- + H₂O
E)H⁺ + OH^- $\to$ H₂O

Question 77

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.82 $\times$ 10^-10)with 0.500 M HCl.Calculate the pH of the solution at the stoichiometric point.

A)5.10
B)9.42
C)2.68
D)11.32
E)none of these

Question 78

A solution containing 10.mmol of and 5.0 mmol of is titrated with 1.8 M HCl.What volume of HCl must be added to reach the first equivalence point?

A)2.8 mL
B)5.6 mL
C)10.6 mL
D)15.6 mL
E)20.6 mL

Question 79

A 0.210-g sample of an acid (molar mass = 192 g/mol)is titrated with [$X] mL of [$Y] M NaOH to a phenolphthalein endpoint.The formula of the acid is:

A)HA
B)H₂A
C)H₃A
D)H₄A
E)not enough information given

Question 80

In titrating 100 mL of 0.10 M HCl (aq)with 0.10 M NaOH,the pH does not change a great deal initially.Why is this?

A)The amount of OH^- has no affect on the pH of aqueous solutions.
B)The H⁺ from the HCl (aq)acts like a buffer.
C)The major species when the acid and base are mixed form a buffered solution.
D)The statement "In titrating 100 mL of 0.10 M HCl (aq)with 0.10 M NaOH,the pH does not change a great deal initially." is not true.
E)None of these.