Deck 8: Applications of Aqueous Equilibria

Question 1

Calculate the pH of a solution prepared by mixing 50 mL of a 0.10 M solution of HF with 25 mL of a 0.20 M solution of NaF. pK_a of HF is 3.14.

A) 5.83
B) 12.00
C) 3.14
D) 7.35
E) 10.80

Answer 1

3.14

Question 2

A student uses 16.60 mL of 0.100 M NaOH to titrate a 0.2000-g sample of an unknown acid. Which of the following acids is the unknown most likely to be? Assume that only the hydrogens bonded to oxygen are titrated by the sodium hydroxide and that, because of experimental error, the student's value may not be identical to the theoretical value.

A) oxalic acid, HOOCCOOH, molar mass 90
B) succinic acid, HOOCCH₂CH₂COOH, molar mass 118
C) benzoic acid, C₆H₅COOH, molar mass 122
D) phthalic acid, C₆H₄ (COOH)₂, molar mass 166
E) not enough information

Answer 2

benzoic acid, C₆H₅COOH, molar mass 122

Question 3

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

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

Answer 3

714 mL HNO₂; 286 mL KNO₂

Question 4

What is the pH of a solution that results when 0.012 mol HNO₃ is added to 670.0 mL of a solution that is 0.26 M in aqueous ammonia and 0.48 M in ammonium nitrate. Assume no volume change. (K_b for NH₃ = 1.8*10^-5.)

A) 8.94
B) 9.57
C) 5.06
D) 8.99
E) 4.43

Question 5

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

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

Question 6

How many mmoles of HCl must be added to 130.0 mL of a 0.40 M solution of methylamine (pK_b = 3.36) to give a buffer having a pH of 11.59?

A) 16 mmol
B) 0.11 mmol
C) 5.2 mmol
D) 2.5 mmol
E) 0.91 mmol

Question 7

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

Question 8

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

Question 9

Calculate the pH of a solution that contains 3.25 M HCN (K_a = 6.2*10^-10), 1.00 M NaOH and 1.50 M NaCN.

A) 8.28
B) 7.46
C) 9.25
D) 8.86
E) none of these

Question 10

Calculate [H⁺] in a solution that is 0.24 M in NaF and 0.46 M in HF. (K_a = 7.2*10^-4)

A) 1.1 * 10^-4 M
B) 1.4 *10^-3 M
C) 1.8 * 10^-2 M
D) 3.8 * 10^-4 M
E) 0.46 M

Question 11

For 110.0 mL of a buffer that is 0.40 M in HOCl and 0.52 M in NaOCl, what is the pH after 11.2 mL of 1.1 M NaOH is added? K_a for HOCl = 3.5 *10^-8. (Assume the volumes are additive.)

A) 7.36
B) 7.57
C) 7.34
D) 7.11
E) 7.80

Question 12

Calculate the pH of a solution made by mixing 49.5 mL of 0.335 M NaA (K_a for HA = 1.0 * 10^-9) with 30.6 mL of 0.120 M HCl.

A) 9.00
B) 9.65
C) 8.45
D) 8.75
E) 9.55

Question 13

Buffers in the human body

A) precipitate proteins so enzymes are inactive.
B) help to keep the body temperature constant.
C) help change the blood plasma pH when foods are eaten.
D) help to maintain a constant blood pH.
E) none of these

Question 14

11.8 mL of 0.30 M HCl is added to a 122.0-mL sample of 0.210 M HNO₂ (K_a for HNO₂ = 4.0*10^-4). What is the equilibrium concentration of NO₂^- ions?

A) 2.9 * 10^-3 M
B) 2.6 * 10^-2 M
C) 4.2*10^-3 M
D) 5.5 * 10^-4 M
E) 9.2 * 10^-3 M

Question 15

A solution contains 0.34 M HA (K_a = 2.0 *10^-7) and 0.17 M NaA. Calculate the pH after 0.05 mol of NaOH is added to 1.00 L of this solution.

A) 6.58
B) 6.70
C) 6.40
D) 6.82
E) 6.19

Question 16

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 *10^-5; K_b for C₅H₅N = 1.7 * 10^-9)

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

Question 17

How much solid NaCN must be added to 1.0 L of a 0.5 M HCN solution to produce a solution with pH 7.0? K_a = 6.2 *10^-10 for HCN.

A) 0.0034 g
B) 0.15 g
C) 160 g
D) 24 g
E) 11 g

Question 18

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* 10^-5.) Assume negligible volume of the HCl.

A) 6.8 * 10^-3 mol
B) 7.5 *10^-2 mol
C) 1.0 *10^-3 mol
D) 5.0 * 10^-1 mol
E) none of these

Question 19

You are given a solution of the weak base Novocain, Nvc. Its pH is 11.00. You add to the solution a small amount of a salt containing the conjugate acid of Novocain, NvcH⁺. Which statement is true?

A) The pH and the pOH remain unchanged.
B) The pH and the pOH both decrease.
C) The pH and the pOH both increase.
D) The pH increases and pOH decreases.
E) The pH decreases and the pOH increases.

Question 20

For ammonia, K_b is 1.8 *10^-5 . To make a buffered solution with pH 10.0, the ratio of NH₄Cl to NH₃ must be

A) 1.8 : 1.
B) 0.18 : 1.
C) 1 : 1.8.
D) 1 : 0.18.
E) none of these

Question 21

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 0.44 M NaOH until a pink color appears; 13.6 mL is required. Find, to within 5%, the number of grams of H₂SO₄ (formula weight = 98) present in 1 L of the battery acid.

A) 480 g
B) 240 g
C) 580 g
D) 290 g
E) 750 g

Question 22

A titration of 100.0 mL of 1.00 M malonic acid (H₂A) was done with 1.00 M NaOH. For malonic acid, K_a1 = 1.49 *10^-2, K_a2 = 2.03 * 10^-6.

-Calculate [H⁺] after 300.0 mL of 1.00 M NaOH has been added.

A) 1.00 * 10^-7 M
B) 4.00 * 10^-14 M
C) 1.41 * 10^-10 M
D) 1.00 M
E) none of these

Question 23

A titration of 100.0 mL of 1.00 M malonic acid (H₂A) was done with 1.00 M NaOH. For malonic acid, K_a1 = 1.49 *10^-2, K_a2 = 2.03 * 10^-6.

-Calculate [H⁺] after 150.0 mL of 1.00 M NaOH has been added.

A) 2.03 *10^-6 M
B) 1.41 * 10^-10 M
C) 1.49 *10^-2 M
D) 1.00 * 10^-7 M
E) none of these

Question 24

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

A) 6.50
B) 3.01
C) 2.41
D) 2.71
E) none of these

Question 25

If 22 mL of 0.50 M HCl is added to 112 mL of 0.20 M NaOH, what is the final pH?

A) 0.78
B) 13.22
C) 12.93
D) 7.00
E) 1.07

Question 26

A 65.5-mL sample of 0.14 M HNO₂ (K_a = 4.0 * 10^-4) is titrated with 0.11 M NaOH. What is the pH after 26.8 mL of NaOH has been added?

A) 10.28
B) 7.00
C) 3.72
D) 2.91
E) 3.07

Question 27

A solution of hydrochloric acid of unknown concentration was titrated with 0.11 M NaOH. If a 150-mL sample of the HCl solution required exactly 12 mL of the NaOH solution to reach the equivalence point, what was the pH of the HCl solution?

A) 11.94
B) 2.09
C) 0.11
D) 2.06
E) -0.14

Question 28

How many moles of HCl(g) must be added to 1.0 L of 2.0 M NaOH to achieve a pH of 0.00? (Neglect any volume change.)

A) 3.0 mol
B)10. mol
C) 1.0 mol
D) 2.0 mol
E) none of these

Question 29

Equal volumes of 0.1 M HCl and 0.1 M HC₂H₃O₂ are titrated with 0.1 M NaOH. Which of the following would be equal for both titrations?

A) the pH at the equivalence point
B) the volume of NaOH added to reach the equivalence point
C) the initial pH
D) the pH at the halfway point
E) two of the above

Question 30

A 10-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)10.
B) 1.0
C) 2.0
D) 4.0
E) impossible to determine

Question 31

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 15.3 mL. What was the concentration of H₂SO₄ in the 5.00-mL sample?

A) 0.306 M
B) 0.765 M
C) 3.06 M
D) 1.53 * 10^-3 M
E) 1.53 M

Question 32

What is the molarity of a sodium hydroxide solution if 25.0 mL of this solution reacts exactly with 22.30 mL of 0.253 M sulfuric acid?

A) 0.284 M
B) 0.451 M
C) 0.567 M
D) 0.226 M
E) 0.113 M

Question 33

What quantity of NaOH(s) must be added to 1.00 L of 0.200 M HCl to achieve a pH of 12.00? (Assume no volume change.)

A) 0.200 mol
B) 0.010 mol
C) 0.210 mol
D) 0.420 mol
E) none of these

Question 34

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

A) 0.20 M NH₃ and 0.20 M NH₄Cl
B) 3.0 M HC₂H₃O₂ and 3.0 M NH₄Cl
C) 0.20 M HC₂H₃O₂ and 0.20 M NaC₂H₃O₂
D) 3.0 M NH₃ and 3.0 M NH₄Cl
E) 3.0 M HC₂H₃O₂ and 3.0 M NH₃

Question 35

A titration of 100.0 mL of 1.00 M malonic acid (H₂A) was done with 1.00 M NaOH. For malonic acid, K_a1 = 1.49 *10^-2, K_a2 = 2.03 * 10^-6.

-Calculate the [H⁺] after 50.00 mL of 1.00 M NaOH has been added.

A) 2.00 * 10^-6 M
B) 1.41 *10^-10 M
C) 1.49 *10^-2 M
D) 3.87 * 10^-2 M
E) none of these

Question 36

A 75.0-mL sample of 0.0500 M HCN (K_a = 6.2 *10^-10) is titrated with 0.500 M NaOH. What is [H⁺] in the solution after 3.0 mL of 0.500 M NaOH has been added?

A) 9.3 *10^-10 M
B) 5.2 * 10^-13 M
C) 1.0 * 10^-7 M
D) 4.1 * 10^-10 M
E) none of these

Question 37

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

A) More data are needed to answer this question.
B) equal to 7.00.
C) greater than 7.00.
D) less than 7.00.

Question 38

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? K_a for HOCl is 3.5*10^-8.

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

Question 39

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

A) HNO₂ + KOH $\rightarrow$ K⁺ + NO₂^- + H₂O
B) H⁺ + OH^- $\rightarrow$ H₂O
C) HNO₂ + OH^- $\rightarrow$ NO₂^- + H₂O
D) HNO₂ + H₂O $\rightarrow$ NO₂^- + H₃O⁺
E) HNO₂ + K⁺ + OH^- $\rightarrow$ KNO₂ + H₂O

Question 40

A 59.00-mL sample of 0.0650 M HCN (K_a = 6.2 * 10^-10) is titrated with 0.670 M NaOH. What volume of 0.670 M NaOH is required to reach the stoichiometric point?

A) 5.72 mL
B) 59.0 mL
C) 608 mL
D) 0.00164 mL
E) 3.84 mL

Question 41

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 10. Which of the following indicator acids would be best to use to mark the endpoint of this titration?

A) indicator A, K_a = 10^-14
B) indicator C, K_a = 10^-8
C) indicator D, K_a = 10^-6
D) indicator B, K_a = 10^-11
E) none of these

Question 42

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 350.0 mL of 0.200 M NaOH is added

A) A^3-
B) HA^2-, A^3-
C) HA^2-
D) OH^-, A^3-
E) H₂A^-, HA^2-

Question 43

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1). The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below:
Which of the following is a major species present at point IV?

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

Question 44

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 200.0 mL of 0.200 M NaOH is added

A) HA^2-, A^3-
B) HA^2-
C) H₂A^-
D) H₂A^-, HA^2-
E) A^3-

Question 45

A certain indicator HIn has a pK_a of 9.00, and a color change becomes visible when 7.00% of it is In^-. At what pH is this color change visible?

A) 6.15
B) 7.88
C) 10.2
D) 3.85
E) none of these

Question 46

After adding 25.0 mL of 0.100 M NaOH to 100.0 mL of 0.100 M weak acid (HA), the pH is found to be 5.90. Determine the value of K_a for the acid HA.

A) 4.2 * 10^-7
B) 3.5 * 10^-9
C) 1.6 *10^-11
D) 2.1 * 10^-5
E) none of these

Question 47

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *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 milliliters, of HCl required to reach a pH of 8.0)

A)
B)
C)
D) [H⁺] = x
E) none of these

Question 48

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 statements is true?

A) At pH 4.7, half of 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 statements are correct.

Question 49

A 100.0-mL sample of 0.2 M (CH₃)₃N (K_b = 5.3 * 10^-5) is titrated with 0.2 M HCl. What is the pH at the equivalence point?

A) 5.4
B) 7.0
C) 10.3
D) 3.1
E) 9.9

Question 50

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) 2.09
D) 5.38
E) 5.53

Question 51

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 *10^-6, K_a2 = 1.0 *10^-10) is titrated with the following volumes of 1.00 M NaOH. 100.0 mL of 1.00 M NaOH

A) 3.35
B) 8.00
C) 3.00
D) 6.00
E) none of these

Question 52

An indicator HIn has K_a = 1 *10^-8. At pH = 6.0, what is the ratio HIn/In^-?

A) 1/100
B) 10/1
C) 1/1
D) 100/1
E) none of these

Question 53

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 0 mL of 0.200 M NaOH is added

A) H₃A, H₂A^-, HA^2-, A^3-
B) H₃A, H₂A^-
C) H₃A
D) H₂A^-, HA^2-
E) H₂A^-

Question 54

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-10) with 0.500 M HCl. Calculate the pH of the solution at the stoichiometric point.

A) 8.70
B) 2.68
C) 11.62
D) -0.85
E) none of these

Question 55

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

A) 7.85
B) 1.30
C) 3.87
D) 1.48
E) 12.52

Question 56

44.4 mL of a 1.42 M NaOH solution is titrated with a 1.90 M HCl solution. What is the final volume of the solution when the NaOH has been completely neutralized by the HCl? (Assume the volumes are additive.)

A) 33.2 mL
B) 77.6 mL
C) 59.4 mL
D) 45.1 mL
E) 104 mL

Question 57

A solution containing 10. mmol of CO₃^2- and 5.0 mmol of HCO₃^- is titrated with 1.0 M HCl.
What volume of HCl must be added to reach the first equivalence point?

A) 5.0 mL
B) 15 mL
C)10. Ml
D) 25 mL
E)20. mL

Question 58

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 11. Which of the following indicators would be best to use to mark the endpoint of this titration?

A) an indicator with K_a = 10^-11
B) an indicator with K_a = 10^-14
C) an indicator with K_a = 10^-10
D) an indicator with K_a = 10^-8
E) an indicator with K_a = 10^-12

Question 59

Methyl orange is an indicator with a K_a of 1 * 10^-4. Its acid form, HIn, is red, while its base form, In^-, is yellow. At pH 6.0, the indicator will be

A) yellow.
B) orange.
C) red.
D) blue.
E) not enough information

Question 60

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1). The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below:
What major species is(are) present at point III?

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

Question 61

A solution containing 10. mmol of CO₃^2- and 5.0 mmol of HCO₃^- is titrated with 1.0 M HCl.
What total volume of HCl must be added to reach the second equivalence point?

A)20. mL
B) 5.0 mL
C)30. mL
D)10. mL
E) 25 mL

Question 62

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 220.0 mL of 0.200 M NaOH is added

A) A^3-
B) OH^-, A^3-
C) H₂A^-, HA^2-
D) HA^2-
E) HA^2-, A^3-

Question 63

A 0.210-g sample of an acid (molar mass = 192 g/mol) is titrated with 30.5 mL of 0.108 M NaOH to a phenolphthalein endpoint. The formula of the acid is

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

Question 64

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) 2.0 * 10² mL
B) 150 mL
C) 250 mL
D) 1.0 *10² mL
E) 50 mL

Question 65

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 * 10^-6, K_a2 = 1.0 * 10^-10) is titrated with the following volumes of 1.00 M NaOH.

-150.0 mL of 1.00 M NaOH

A) 6.00
B) 6.48
C) 8.00
D) 8.50
E) None of these

Question 66

A 5.95-g sample of an acid, H₂X, requires 45.0 mL of a 0.500 M NaOH solution for complete reaction (removing both protons). What is the molar mass of the acid expressed in grams per mol?

A) 529
B) 264
C) 178
D) 132
E) none of these

Question 67

A 135.0-mL sample of a 0.25 M solution of H₃PO₄ is titrated with 0.12 M NaOH. What volume of base must be added to reach the third equivalence point?

A) 5.6 *10² mL
B) 2.8* 10² mL
C) 8.4 *10² mL
D) 1.9 * 10² mL
E) 94 mL

Question 68

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 75.0 mL of 0.200 M NaOH is added

A) H₂A^-
B) HA^2-
C) H₃A, H₂A^-
D) H₂A^-, HA^2-
E) H₃A

Question 69

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1). 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) 7.95
B) 12.39
C) 10
D) 11.79
E) none of these

Question 70

For carbonic acid (H₂CO₃), K_a1 = 4.30 *10^-7 and K_a2 = 5.62 *10^-11. Calculate the pH of a 0.50 M solution of Na₂CO₃.

A) 11.97
B) 8.31
C) 10.67
D) 2.03
E) 3.33

Question 71

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 * 10^-6, K_a2 = 1.0 * 10^-10) is titrated with the following volumes of 1.00 M NaOH.

-0 mL of 1.00 M NaOH

A) 3.00
B) 6.00
C) 0
D) 3.35
E) None of these

Question 72

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 * 10^-6, K_a2 = 1.0 * 10^-10) is titrated with the following volumes of 1.00 M NaOH.

-200.0 mL of 1.00 M NaOH

A) 9.50
B) 6.48
C) 6.00
D) 8.00
E) None of these

Question 73

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 300.0 mL of 0.200 M NaOH is added

A) A^3-
B) OH^-, A^3-
C) H₃A, H₂A^-, HA^2-, A^3-
D) H₂A^-, OH^-
E) OH^-, HA^2-, A^3-

Question 74

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
After 100.0 mL of 0.200 M NaOH is added

A) H₃A, HA^2-, A^3-
B) H₂A^-, HA^2-
C) H₃A, H₂A^-
D) H₂A^-
E) HA^2-

Question 75

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 * 10^-6, K_a2 = 1.0 * 10^-10) is titrated with the following volumes of 1.00 M NaOH.

-250.0 mL of 1.00 M NaOH

A) 10.00
B) 9.52
C) 8.00
D) 9.00
E) None of these

Question 76

You dissolve 1.24 g of an unknown diprotic acid in 220.0 mL of H₂O. This solution is just neutralized by 6.44 mL of a 1.25 M NaOH solution. What is the molar mass of the unknown acid?

A) 1.28 * 10² g/mol
B) 3.08 * 10² g/mol
C) 2.10 * 10² g/mol
D) 1.54 * 10² g/mol
E) 1.93 *10² g/mol

Question 77

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1). The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below:
What is the pH at point III?

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

Question 78

Consider the titration of 200.0 mL of a 0.100 M solution of the weak acid H₂A with 0.200 M NaOH. The first equivalence point is reached after 100.0 mL of 0.200 M NaOH has been added, and the pH is 6.27. The pH after 65.0 mL of 0.200 M NaOH has been added, the pH is 4.95. Calculate the pH of the original acid (no NaOH added).

A) 3.19
B) 2.84
C) 2.55
D) 4.68
E) none of these

Question 79

A solution contains 25 mmol of H₃PO₄ and 10. mmol of NaH₂PO₄. What volume of 2.0 M NaOH must be added to reach the second equivalence point of the titration of the H₃PO₄ with NaOH?

A)60. mL
B)30. mL
C) 5.0 mL
D) 12 mL
E) 25 mL

Question 80

In the titration of 100.0 mL of a 0.200 M solution of H₂A (K_a1 = 1.0 * 10^-5, K_a2 = 1.0 * 10^-8), what volume of 0.400 M NaOH must be added to reach a pH of 5.00?

A) 25.0 mL
B) 100.0 mL
C) 0 mL
D) 150.0 mL
E) 50.0 mL