Deck 17: Additional Aspects of Acid-Base Equilibria

Question 1

In 0.100 M HC2H3O2(aq), [H3O+(aq)] = [C2H3O2-(aq)] = 1.3 x 10-3 M. If a few drops of concentrated HCl(aq) are added to this solution, the C2H3O2-(aq) concentration is:

A) < 1.3 x 10-3 M
B) > 1.3 x 10-3 M
C) = 1.3 x 10-3 M
D) 0.100 M

Answer 1

< 1.3 x 10-3 M

Question 2

The pH of a buffer solution changes only slightly with addition of a small amount of acid or base.

Answer 2

True

Question 3

In the titration of a solution of HCN(aq) with NaOH(aq), the equivalence point occurs at a pH greater than 7.

Answer 3

True

Question 4

What is the [H₃O⁺] of a solution measured to be 0.20 M in sodium acetate and 0.40 M in acetic acid? [Ka = 1.8 × 10^-5]

A) 1.8 × 10^-5 M
B) 9.0 × 10^-6M
C) 3.6 × 10^-5 M
D) 7.2 × 10^-5M
E) 4.7 M

Question 5

Which among the following pairs is inefficient as buffer pair?

A) ammonium chloride and ammonium hydroxide
B) sodium chloride and sodium hydroxide
C) boric acid and sodium borate
D) potassium carbonate and potassium bicarbonate
E) potassium bromide and hydrobromic acid

Question 6

A salt of a polyprotic acid such as NaHCO3 cannot act as an acid.

Question 7

The color change range of most acid-base indicators is 1 pH unit.

Question 8

The common ion in a mixture of a weak acid and a strong acid is the hydronium ion.

Question 9

How will addition of sodium acetate to an acetic acid solution affect the pH?

A) It will lower the pH.
B) The pH will not change.
C) The solution becomes hotter.
D) The pH cannot be measured.
E) It will raise the pH.

Question 10

Acid-base indicators have two forms: an acid of one color and a base of another color.

Question 11

How will addition of sodium chloride affect the pH of a HCl solution?

A) It will lower the pH.
B) The pH will not change.
C) The solution becomes hotter.
D) The pH cannot be measured.
E) It will raise the pH.

Question 12

For an accurate titration, the end point needs to match the equivalence point.

Question 13

The common ion in a mixture of a weak base and a strong base is the hydronium ion.

Question 14

A weak acid-strong base will produce a longer vertical section of a titration curve than will a strong acid-strong base.

Question 15

What is the concentration of the acetate ion of a solution measured to be 0.20 M acetic acid and 0.20 M in hydrochloric acid? [Ka for acetic acid = 1.8 × 10-5]

A) 3.6 × 10-5 M
B) 9.0 × 10-6 M
C) 1.8 × 10-5 M
D) 7.2 × 10-5 M
E) 0.20 M

Question 16

A strong acid and its conjugate base will form a buffer.

Question 17

The pH of a buffer depends mainly on the pKa of the weak acid component of the buffer.

Question 18

Ten milliliters of 0.10 M NH3(aq) (K = 1.8 × 10-5) is mixed with 10 mL of 0.10 M NH4Cl. Neglecting the differences between activities and concentrations, the resulting solution:

A) has a pH = 4.74
B) has a [H+] of approximately 10-3 M
C) has a [NH4+] greater than that of the NH4Cl(aq)
D) has an [OH-] of 1.8 × 10-5 M
E) is acidic

Question 19

If some NH4Cl is added to an aqueous solution of NH3:

A) the pH of the solution will increase
B) the pH of the solution will decrease
C) the solution will not have pH
D) the pH of the solution will not change
E) NH4Cl cannot be added to NH3

Question 20

A solution of sodium carbonate is easier to calculate the pH than sodium hydrogen carbonate because there is only one hydrolysis reaction instead of two.

Question 21

Phenolphthalein may be used as an indicator for the titration of:

A) a weak base with a strong acid
B) a weak acid with a weak base
C) any acid and base
D) a weak acid with a strong base
E) phenolphthalein cannot be used as an indicator

Question 22

What factor governs the selection of an indicator for a neutralization titration?

A) the final volume of the solution
B) the volume of titrant
C) the molarity of the standard solution
D) the pH at the stoichiometric (equivalence) point
E) the solubility of the indicator

Question 23

Which of the following mixtures would you dismiss as a potential buffer in a laboratory?

A) mixing equal volumes of 0.10 M NaC2H3O2(aq) and 0.10 M HCl(aq).
B) mixing equal volumes of 0.10 M NaC2H3O2(aq) and 0.050 M HCl(aq).
C) mixing equal volumes of 0.10 M NaC2H3O2(aq) and 0.10 M HC2H3O2(aq).
D) mixing equal volumes of 0.10 M HC2H3O2(aq) and 0.050 M NaOH(aq).

Question 24

In the titration of 50.0 mL of 0.0200 M C6H5COOH(aq) with 0.100 M NaOH(aq), what is/are the major species in the solution after the addition of 5.0 mL of NaOH(aq)?

A) C6H5COOH, C6H5COO-, and Na+
B) C6H5COOH
C) C6H5COO- and Na+
D) C6H5COOH, OH-, and Na+

Question 25

Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0. State what color the indicator will assume in the following solution: 0.10 M NH4NO3

A) red
B) yellow
C) red-yellow mixture
D) The indicator is its original color.
E) There is not enough information to answer this question.

Question 26

Which of the following can act as buffer solutions?
I. 0.1 M HC₂H₃O₂/0.1 M NaC₂H₃O₂
II. 0.1 M NH₃/0.1 M NH₄Cl
III. 0.1 M HNO₃/0.1 M NaNO₃
IV. 0.1 M H₂SO₃/0.1 M NaHSO₃
V. 0.1 M KHSO₄/ 0.1 M H₂SO₄

A) I), II), and III)
B) II), III) and IV)
C) III) and IV)
D) I), II) and IV)
E) III), IV) and V)

Question 27

Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0. State what color the indicator will assume in the following solution: 0.1 M NaCl

A) red
B) yellow
C) red-yellow mixture
D) orange
E) The indicator keeps its original colour.

Question 28

The following compounds are available as 0.10 M aqueous solutions: pyridine (pKb = 8.82), triethylamine (pKb = 3.25), HClO4, NaOH, phenol (pKa = 9.96), HClO (pKa = 7.54), and NH3 (pKb = 4.74). Identify two solutions that could be used to prepare a buffer with a pH of approximately 5.

A) pyridine and HClO4
B) triethyamine and HClO4
C) phenol and NaOH
D) HClO and NaOH

Question 29

A solution containing equimolar amounts of a weak acid with Ka = 10-5 and its sodium salt has:

A) pH > 7
B) pH < 7
C) pH = 7
D) pH dependent on concentration ratios
E) pH dependent on the nature of the acid anion

Question 30

Which of the following statements correctly describe a typical titration curve for the titration of a strong acid by a strong base?
I. The beginning pH is low.
II. The pH change is slow until near the equivalence point.
III. At the equivalence point, pH changes by a large value.
IV. Beyond the equivalence point, pH rises rapidly.
V. The equivalence point would be at a pH less than 3.5.

A) I), III) and V)
B) II), III) and IV)
C) I), III) and IV)
D) III), IV) and V)
E) I), II) and III)

Question 31

Choose the correct statement.

A) 30 mL of 2 molar H3PO4 will exactly react with 15 mL of a 2 molar NaOH solution.
B) One liter of 1 molar HCl will exactly neutralize 2 liters of 0.5 molar NaOH.
C) A 1 molal solution always contains exactly 1 mole in a liter of solution.
D) One liter of a 1 molar solution of an acid always exactly neutralizes one liter of a one molar solution of a base.
E) A 1 molar solution requires 2 moles of H2SO4 per liter of solution.

Question 32

Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0. State what color the indicator will assume in the following solution: 0.10 M NaCN

A) red
B) yellow
C) red-yellow mixture
D) The indicator is its original color.
E) There is not enough information to answer this question.

Question 33

The solution that is added from the burret during a titration is the:

A) buffer
B) titrant
C) indicator
D) base
E) titrator

Question 34

What is the buffer range (for an effective 2.0 pH unit) for a benzoic acid/sodium benzoate buffer? [Ka for benzoic acid is 6.3 × 10-5]

A) 8.8 - 10.8
B) 7.4 - 9.4
C) 5.3 - 7.3
D) 4.7 - 6.7
E) 3.2 - 5.2

Question 35

The Henderson-Hasselbach equation, used to calculate the pH of simple conjugate-pair buffer systems, would be expressed for an ammonia/ammonium chloride buffer, for which Kb(NH3) is 1.8 × 10-5, as:

A) pH = 4.74 + log([NH3]/[NH4+])
B) pH = 4.74 + log([NH4+]/[NH3])
C) pH = 9.25 + log([NH3]/[NH4+])
D) pH = 9.25 + log([NH4+]/[NH3])
E) pH = 14.0 - log(1.8 × 10-5)

Question 36

Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0. State what color the indicator will assume in the following solution: 0.20 M KOH

A) red
B) yellow
C) red-yellow mixture
D) orange
E) The indicator keeps its original colour.

Question 37

Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0. State what color the indicator will assume in the following solution: 0.10 M HC2H3O2

A) red
B) yellow
C) red-yellow mixture
D) The indicator is its original color.
E) There is not enough information to answer this question.

Question 38

For the following titration, determine whether the solution at the equivalence point is acidic, basic or neutral and why: HCl is titrated with NH3(aq)

A) acidic because of hydrolysis of NH4+
B) basic because of hydrolysis of NH3
C) acidic because of hydrolysis of Cl-
D) acidic because of hydrolysis of HCl
E) neutral salt of strong acid and strong base

Question 39

Which of the pH indicators from the list above would be most appropriate for the titration of 0.30 M acetic acid (Ka = 1.8 × 10-5) with 0.15 M sodium hydroxide?

A) methyl orange
B) litmus
C) thymol blue
D) trinitrobenzene
E) Both thymol blue and litmus can be used.

Question 40

Which condition characterizes the stoichiometric point of a neutralization titration?

A) Equivalent amounts of acid and base have reacted.
B) The pH is exactly 7.0.
C) The indicator changes color.
D) A slight excess of titrant is present.
E) A slight excess of indicator is present.

Question 41

Calculate the pH of a 1.00 L solution of 0.100 M NH3(aq) after the addition of 0.010 mol NH4Cl(s). For NH3, pKb = 4.74.

A) 10.26
B) 9.26
C) 8.26
D) 11.56

Question 42

A weak acid has Ka = 1.00 × 10-3. If [HA] = 1.00 M what must be [A-] for the pH to be 2.7?

A) 0.50 M
B) 2.0 M
C) 2.7 M
D) 0.37 M
E) 0.75 M

Question 43

Determine the [C2H3O2-] of the following solution. Initial concentrations are given. [HC2H3O2] = 0.250 M, [HI] = 0.120 M [Ka = 1.8 × 10-5]

A) 8.6 × 10-6 M
B) 3.8 × 10-5 M
C) 1.8 × 10-5 M
D) 0.25 M
E) 0.37 M

Question 44

The titration curve for 10.0 mL of 0.100 M H3PO4(aq) with 0.100 M NaOH(aq) is given below. Estimate the pKa2 of H3PO4.

A) 7.2
B) 4.8
C) 9.8
D) 2.2

Question 45

Determine the pH of the following solution. Initial concentrations are given. [HF] = 1.296 M, [NaF] = 1.045 M, Ka for HF is 6.6 × 10-4

A) 10.73
B) 3.27
C) 3.18
D) 3.09
E) 11.91

Question 46

In the neutralization of 50.0 mL of 0.1 M BOH (a weak base with Kb = 1.6 × 10-7) with 0.10 M H2SO4, the most correct description of the solution at the mid-point of the titration, i.e., half neutralized, is:

A) a solution in which [B+] essentially equals [BOH]
B) a solution in which [B+] essentially equals 4 × 10-4 M
C) a solution whose volume is 75 mL and contains some undissociated BOH molecules and some B+, OH-, and HSO4- ions
D) a solution containing SO42- and B2+ ions
E) a solution in contact with BSO4 solid

Question 47

Determine the pH of the following solution. Initial concentrations are given. [HC2H3O2] = 0.250 M, [HCl] = 0.120 M [Ka = 1.8 × 10-5]

A) 0.60
B) 0.92
C) 0.43
D) 4.74
E) 13.08

Question 48

For the following titration, determine whether the solution at the equivalence point is acidic, basic, or neutral and why: NaHCO3(aq) titrated with NaOH(aq)

A) basic because of excess OH-
B) acidic because of hydrolysis of HCO3-
C) acidic because of hydrolysis of Na+
D) neutral salt of strong acid and strong base
E) basic because of hydrolysis of CO32-

Question 49

For the following titration, determine whether the solution at the equivalence point is acidic, basic or neutral and why: KOH is titrated with HI(aq)

A) basic because of hydrolysis of K+
B) basic because of hydrolysis of KOH
C) acidic because of hydrolysis of OH-
D) acidic because of hydrolysis of HI
E) neutral salt of strong acid and strong base

Question 50

Why do we avoid titrating ammonia with acetic acid?

A) The change in pH near the end point is not large enough to be accurately detected.
B) There is no known indicator which changes color at the right pH.
C) The reaction is too slow.
D) There is not enough difference between the ionization constants of ammonia and acetic acid.
E) Ammonia does not react with acetic acid.

Question 51

Determine the pH of the following solution. Initial concentrations are given. [HC2H3O2] = 0.250 M, [NaC2H3O2] = 0.120 M [Ka = 1.8 × 10-5]

A) 5.1
B) 4.4
C) 8.9
D) 9.6
E) 7.0

Question 52

Choose the expression that gives the molar concentration of a H2SO4 solution if 24.3 mL of a 0.105 M NaOH solution is required to titrate 60 mL of the acid.

A) (60 × 24.3)/0.105
B) (60 × 2)/(24.3 × 0.105)
C) (24.3 × 0.105)/(60)
D) (24.3 × 0.105)/(60 × 2)
E) (60 × 0.105)/(2 × 24.3)

Question 53

A solution of an unknown acid had a pH of 3.70. Titration of a 25.0 mL aliquot of the acid solution required 21.7 mL of 0.104 M sodium hydroxide for complete reaction. Assuming that the acid is monoprotic, what is its ionization constant?

A) 9.0 × 10-2
B) 2.0 × 10-4
C) 4.4 × 10-7
D) 3.6 × 10-9
E) 2.7 × 10-11

Question 54

Assuming no volume change on mixing, what mass of ammonium chloride should be added to 250.0 mL of 0.25 M ammonia to produce a solution of pH 10.70? [Kb for ammonia is 1.8 × 10-5]

A) 3.7 mg
B) 120 mg
C) 40 mg
D) 30 mg
E) 80 mg

Question 55

What is the pH of a solution prepared by mixing equal volumes of 0.10 M hydrochloric and 0.1 M hydrofluoric acid? [Ka for HF is 6.6 × 10-4]

A) 1.0
B) 1.3
C) 1.6
D) 2.2
E) 5.0

Question 56

Calculate the pH of a 1.00 L solution of 0.100 M NH3(aq) after the addition of 0.010 mol HCl(g). For NH3, pKb = 4.74.

A) 10.21
B) 9.26
C) 8.31
D) 11.46

Question 57

Determine the [F-] of the following solution. Initial concentrations are given. [HF] = 1.296 M, [NaF] = 1.045 M, Ka for HF is 6.6 × 10-4

A) 1.046 M
B) 2.344 M
C) 5.3 × 10-4 M
D) 8.2 × 10-4 M
E) 0.251 M

Question 58

A weak acid has Ka = 4.2 × 10-3. If [A-] = 2.0 M, what must [HA] be so that [H+] = 2.1 × 10-3 M?

A) 1.5 M
B) 2.0 M
C) 1.0 M
D) 0.5 M
E) 0.25 M

Question 59

Determine the pH of the following solution. Initial concentrations are given. [HF] = 1.296 M, [HCl] = 1.045 M, Ka for HF is 6.6 × 10-4

A) 14
B) 3.1
C) 3.2
D) -0.019
E) 0.60

Question 60

In a solution prepared by mixing equal volumes of 0.20 M acetic acid and 0.20 M hydrobromic acid, the common ion is ________.

A) Br-
B) C2H3O22-
C) H2C2H3O2
D) H2Br+
E) H3O+

Question 61

What is the change in pH after addition of 10.0 mL of 1.0 M sodium hydroxide to 90.0 mL of a 1.0 M NH3/1.0 M NH4+ buffer? [Kb for ammonia is 1.8 × 10-5]

A) 1.0 pH unit
B) 0.1 pH unit
C) 0.01 pH unit
D) 0.001 pH unit
E) zero

Question 62

How many mL of 0.200 M acetic acid are mixed with 13.2 mL of 0.200 M sodium acetate to give a buffer with pH = 4.2?

A) 37 mL
B) 18 mL
C) 3.8 mL
D) 14 mL
E) 46 mL

Question 63

A solution has [HC7H5O2] = 0.100 M and [Ca(C7H5O2)2] = 0.200 M. Ka = 6.3 × 10-5 for HC7H5O2. The solution volume is 5.00 L. What is the pH of the solution after 10.00 ml of 5.00 M NaOH is added?

A) 4.80
B) 4.86
C) 4.65
D) 4.70
E) 4.75

Question 64

What is the pH of a solution made by dissolving 2.16 g of sodium benzoate (NaC6H5CO2) in a sufficient volume of 0.033 M benzoic acid solution to prepare 500.0 mL of buffer? [Ka for benzoic acid is 6.3 × 10-5]

A) 4.16
B) 4.37
C) 4.64
D) 5.77
E) 6.30

Question 65

What mass of sodium acetate should be dissolved in 250.0 mL of 0.30 M acetic acid to form a buffer of pH 5.0? [Ka for acetic acid is 1.8 × 10-5]

A) 11 g
B) 8.0 g
C) 7.5 g
D) 5.0 g
E) 1.4 g

Question 66

A buffer was prepared by adding 2.4 g of ammonium nitrate to 100.0 mL of 0.30 M ammonia (Kb = 1.8 × 10-5). To this solution was then added 10.0 mL of 0.30 M sodium hydroxide, which caused a pH change of ________.

A) 3.0 pH units
B) 0.30 pH units
C) 0.90 pH units
D) 0.09 pH units
E) zero

Question 67

A solution has [HC7H5O2] = 0.100 M and [Ca(C7H5O2)2] = 0.200 M. Ka = 6.3 × 10-5 for HC7H5O2. The solution volume is 5.00 L. What is the pH of this solution after 5.00 ml 10.0 M HCl is added?

A) 4.80
B) 4.86
C) 4.65
D) 4.70
E) 4.75

Question 68

For HClO2, Ka = 1.2 × 10-2. What is the pH of a solution in which [NaClO2] = 0.193 M and [HClO2] = 0.203 M?

A) 3.32
B) 0.11
C) 1.92
D) 1.94
E) 1.90

Question 69

A handbook states that to prepare a particular buffer solution mix 39.0 mL of 0.20 M NaH2PO4 with 61.0 mL of 0.20 M Na2HPO4. What will be the pH of this buffer?

A) 7.2
B) 7.4
C) 7.0
D) 6.8
E) 6.6

Question 70

Twenty-five milliliters of 0.10 M HCl is titrated with 0.10 M NaOH. What is the pH at equivalence?

A) 7.0
B) 6.2
C) 7.5
D) 8.6
E) 7.1

Question 71

A buffer is 0.282 M C6H5COOH(aq) and 0.282 M Na(C6H5COO)(aq). Calculate the pH after the addition of 0.150 moles of nitric acid to 1.0 L of the buffer. For C6H5COOH, pKa = 4.20.

A) 3.69
B) 4.20
C) 4.71
D) 3.87

Question 72

What is the pH of a buffer solution prepared by dissolving 25.5 g NaC2H3O2 in a sufficient volume of 0.550 M HC2H3O2 to make 500.0 mL of buffer?

A) 4.74
B) 4.68
C) 4.91
D) 4.57
E) 4.79

Question 73

The buffer capacity of a solution may be defined as the number of moles of H+ that will change the pH of 1.00 L of the buffer by 1.00 pH units. What is the buffer capacity of a solution which is 0.10 M in acetic acid (Ka = 1.8 × 10-5) and 0.30 M in sodium acetate, in units of mol (H+) per liter?

A) 0.20
B) 0.10
C) 0.087
D) 0.009
E) zero

Question 74

An acid has a Ka = 1 × 10-6. At what pH would this acid and its corresponding salt make a good buffer?

A) 6
B) 7
C) 8
D) 5
E) 4

Question 75

A pH 4.88 buffer was prepared by dissolving 0.10 mol of benzoic acid (Ka = 6.3 × 10-5) and 0.50 mol of sodium benzoate in sufficient pure water to form a 1.00 L solution. To a 70.0 mL aliquot of this solution was added 2.00 mL of 2.00 M HI solution. What was the pH of the new 72.0 mL solution?

A) 2.84
B) 3.16
C) 3.36
D) 4.65
E) 4.90

Question 76

What will the pH at the neutralization point of 0.00812 M Ba(OH)2 be when titrated with HCl?

A) 7.0
B) 12.2
C) 8.0
D) 9.0
E) 6.0

Question 77

If 30.0 mmol HCl(g) is added to 1.00 L of a buffer that is 0.340 M NH3(aq) and 0.290 M NH4Cl(aq), what are the final concentrations of NH3(aq) and NH4Cl(aq), respectively? Assume no volume change.

A) 0.310 M and 0.320 M
B) 0.310 M and 0.290 M
C) 0.370 M and 0.290 M
D) 0.370 M and 0.320 M

Question 78

What is the pH of a buffer that is 0.88 M HCN(aq) and 0.53 M NaCN(aq)? The Ka of HCN is 6.2 x 10-10.

A) 8.99
B) 9.21
C) 9.43
D) 4.79

Question 79

A pH 9.56 buffer was prepared by mixing 2.00 moles of ammonia (Kb for ammonia is 1.8 × 10-5) and 1.00 mol of ammonium chloride in water to form a solution with a volume of 1.00 L. To a 200.0 mL aliquot of this solution was added 10.0 mL of 10.0 M sodium hydroxide. What was the resulting pH?

A) 9.28
B) 9.56
C) 9.95
D) 10.50
E) 13.7

Question 80

A handbook states that to prepare a particular buffer solution mix 63.0 mL of 0.200 M HC2H3O2 with 37.0 mL of 0.200 M NaC2H3O2. What is the pH of this buffer? (Ka = 1.8 × 10-5)

A) 4.74
B) 4.51
C) 4.98
D) 5.33
E) 7.00