Deck 17: Additional Aspects of Acidbase Equilibria

Question 1

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

Answer 1

False

Question 2

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

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

Answer 2

3.6 × 10^-5 M

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

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 5

The neutralization of a weak acid with a strong base will produce a longer vertical section of a titration curve than will a strong acid with a strong base.

Question 6

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

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

Question 7

How will addition of sodium chloride affect the pH of a HCl(aq)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 8

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

Question 9

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

Question 10

The common ion in an aqueous solution of a weak acid and a strong acid is the hydronium ion.

Question 11

Mixing comparable amounts of a strong acid and its conjugate base will form a buffer.

Question 12

How will addition of sodium acetate to an aqueous 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 13

What is the concentration of the acetate ion of an aqueous solution measured to be 0.20 M acetic acid in 0.20 M hydrochloric acid? (K_a 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 14

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

Question 15

Which among the following pairs is inefficient as buffer pair?

A)ammonia and ammonium chloride
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 16

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

Question 17

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

Question 18

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

Question 19

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

Question 20

Ten milliliters of 0.10 M NH₃(aq)(K_b = 1.8 × 10^-5)is mixed with 10 mL of 0.10 M NH₄Cl(aq).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 21

Choose the correct statement.

A)30 mL of 2 molar H₃PO₄(aq)will exactly react with 15 mL of a 2 molar NaOH(aq)solution.
B)One liter of 1 molar HCl(aq)will exactly neutralize 2 liters of 0.5 molar NaOH(aq).
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(aq)per liter of solution.

Question 22

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,IIIand IV
C)IIIand IV
D)I,IIand IV
E)III,IVand V

Question 23

An aqueous solution containing equimolar amounts of a weak acid with K_a = 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 24

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(aq).

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

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: 0.20 M KOH(aq).

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

Question 26

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⁺
E)C₆H₅COOH,OH^-,Na⁺,C₆H₅COO^-

Question 27

For the following titration,determine whether the solution at the equivalence point is acidic,basic or neutral and why:
HCl(aq)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 28

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 29

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

A)pyridine and HClO₄
B)triethylamine and HClO₄
C)phenol and NaOH
D)HClO and NaOH
E)HClO and NH₃

Question 30

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)
E)mixing equal volumes of 0.10 M NH₃(aq)and 0.10 M of NH₄Cl(aq)

Question 31

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 K_b(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 32

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 33

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(aq).

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 34

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(aq).

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 35

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

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

Question 36

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,IIIand IV
C)I,IIIand IV
D)III ,IV and V
E)I,IIand III

Question 37

methyl orange: red at pH < 3.1: orange at pH 3.1-4.4: yellow-orange above pH 4.4
Litmus: red at pH < 4.5: purple at pH 4.5-8.3: blue above pH 8.3
Thymol blue: yellow at pH < 8.0: green at pH 8.0-9.6: blue above pH 9.6
Trinitrobenzene: colorless at pH < 12: yellow at pH 12.0-1: orange above pH 14.0
Which of the pH indicators from the list above would be most appropriate for the titration of 0.30 M aqueous acetic acid (K_a = 1.8 × 10^-5)with 0.15 M aqueous sodium hydroxide?

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

Question 38

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 39

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(aq).

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 40

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 41

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

A)Br^-
B)C₂H₃O₂^2-
C)H₂C₂H₃O₂
D)H₂Br⁺
E)H₃O⁺

Question 42

A weak acid has K_a = 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 43

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

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

Question 44

Determine the pH of the following aqueous solution.Initial concentrations are given.
[HC₂H₃O₂] = 0.250 M,[HCl] = 0.120 M K_a (acetic acid)= 1.8 × 10^-5

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

Question 45

An aqueous 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 aqueous 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 46

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,pK_b = 4.74.

A)10.21
B)9.26
C)8.31
D)11.46
E)7.00

Question 47

Determine the pH of the following aqueous solution.Initial concentrations are given.
[HC₂H₃O₂] = 0.250 M,[NaC₂H₃O₂] = 0.120 M ,K_a ( acetic acid)= 1.8 × 10^-5

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

Question 48

A buffer was prepared by adding 2.4 g of ammonium nitrate to 100.0 mL of 0.30 M aqueous ammonia (K_b = 1.8 × 10^-5).To this solution was then added 10.0 mL of 0.30 M aqueous 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 49

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,pK_b = 4.74.

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

Question 50

Determine the [F^-] of the following aqueous solution.Initial concentrations are given.
[HF] = 1.296 M,[NaF] = 1.045 M,K_a 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 51

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

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

Question 52

Determine the [C₂H₃O₂^-] of the following aqueous solution.Initial concentrations are given.
[HC₂H₃O₂] = 0.250 M,[HI] = 0.120 M K_a (acetic acid)= 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 53

What is the pH of a solution prepared by mixing equal volumes of 0.10 M aqueous hydrochloric and 0.1 M aqueous hydrofluoric acid? (K_a for HF is 6.6 × 10^-4)

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

Question 54

Choose the expression that gives the molar concentration of a H₂SO₄(aq)solution if 24.3 mL of a 0.105 M NaOH(aq)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 55

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 CO₃^2-

Question 56

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

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

Question 57

The titration curve for 10.0 mL of 0.100 M H₃PO₄(aq)with 0.100 M NaOH(aq)is given below.
Estimate the pK_a2 of H₃PO₄.

A)7.2
B)4.8
C)9.8
D)2.2
E)6.5

Question 58

A weak acid has K_a = 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 59

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 60

For the following titration,determine whether the solution at the equivalence point is acidic,basic or neutral and why:
KOH(aq)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 61

How many mL of 0.200 M aqueous acetic acid are mixed with 13.2 mL of 0.200 M aqueous sodium acetate to give a buffer with pH = 4.2? (K_a for acetic acid is 1.8 × 10^-5)

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

Question 62

What is the change in pH after addition of 10.0 mL of 1.0 M aqueous sodium hydroxide to 90.0 mL of an aqueous 1.0 M NH₃/1.0 M NH₄⁺ buffer? (K_b 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 63

An aqueous solution has [HC₇H₅O₂] = 0.100 M and [Ca(C₇H₅O₂)₂] = 0.200 M.K_a = 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

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 an aqueous solution which is 0.10 M in acetic acid (K_a = 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 65

A pH 4.88 buffer was prepared by dissolving 0.10 mol of benzoic acid (K_a = 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 aqueous 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 66

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

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

Question 67

For HClO₂,K_a = 1.2 × 10^-2.What is the pH of an aqueous 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 68

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

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

Question 69

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 70

A handbook states that to prepare a particular buffer solution mix 39.0 mL of 0.20 M aqueous NaH₂PO₄ with 61.0 mL of 0.20 M aqueous Na₂HPO₄.What will be the pH of this buffer? For phosphoric acid Ka₂= 6.2 × 10^-8

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

Question 71

An aqueous solution has [HC₇H₅O₂] = 0.100 M and [Ca(C₇H₅O₂)₂] = 0.200 M.K_a = 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(aq)is added?

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

Question 72

What mass of sodium acetate should be dissolved in 250.0 mL of 0.30 M aqueous acetic acid to form a buffer of pH 5.0? (K_a 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 73

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 aqueous benzoic acid solution to prepare 500.0 mL of buffer? [K_a for benzoic acid is 6.3 × 10^-5]

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

Question 74

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

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

Question 75

An acid has a K_a = 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 76

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

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

Question 77

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

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

Question 78

What volume in mL of 2.0 M H₂SO₄(aq)is needed to neutralize 7.8 g of Al(OH)₃(78.0 g/mol)? Al₂(SO₄)₃(aq)and water are the titration products.

A)150 mL
B)75 mL
C)300 mL
D)500 mL
E)250 mL

Question 79

A buffer is 0.282 M C₆H₅COOH(aq)and 0.282 M C₆H₅COONa(aq).Calculate the pH after the addition of 0.150 moles of nitric acid to 1.0 L of the buffer.For C₆H₅COOH,pK_a = 4.20.

A)3.69
B)4.20
C)4.71
D)3.87
E)7.00

Question 80

A pH 9.56 buffer was prepared by mixing 2.00 moles of ammonia (K_b 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 aqueous sodium hydroxide.What was the resulting pH?

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