acid ionization constant (K_a)

equilibrium constant for an acid ionization reaction

base ionization constant (K_b)

equilibrium constant for a base ionization reaction

observation that acid-base strength of solutes in a given solvent is limited to that of the solvent’s characteristic acid and base species (in water, hydronium and hydroxide ions, respectively)

ternary compound with acidic properties, molecules of which contain a central nonmetallic atom bonded to one or more O atoms, at least one of which is bonded to an ionizable H atom

ratio of the concentration of ionized acid to initial acid concentration expressed as a percentage

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Chemistry 2e · 14.3 Relative Strengths of Acids and Bases

Relative Strengths of Acids and Bases: practice problems

22 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 27
Explain why the neutralization reaction of a weak acid and a strong base gives a weakly basic solution.
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Exercises 29
The odor of vinegar is due to the presence of acetic acid, CH₃CO₂H, a weak acid. List, in order of descending concentration, all of the ionic and molecular species present in a 1-M aqueous solution of this acid.
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Exercises 31
Explain why the ionization constant, K $_{a}$ , for H₂SO₄ is larger than the ionization constant for H₂SO₃.
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Exercises 33
Gastric juice, the digestive fluid produced in the stomach, contains hydrochloric acid, HCl. Milk of Magnesia, a suspension of solid Mg(OH)₂ in an aqueous medium, is sometimes used to neutralize excess stomach acid. Write a complete balanced equation for the neutralization reaction, and identify the conjugate acid-base pairs.
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Exercises 35
What is the ionization constant at 25 °C for the weak acid $CH_{3} NH_{3}^{+},$ the conjugate acid of the weak base CH₃NH₂, K $_{b}$ = 4.4 $\times$ 10⁻⁴.
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Exercises 37
Which base, CH₃NH₂ or (CH₃)₂NH, is the stronger base? Which conjugate acid, $(CH_{3})_{2} NH_{2}^{+}$ or $CH_{3} NH_{3}^{+}$ , is the stronger acid?
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Exercises 39
Which is the stronger base, (CH₃)₃N or $H_{2} BO_{3}^{-} ?$
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Exercises 41
Predict which compound in each of the following pairs of compounds is more acidic and explain your reasoning for each.
(a) $HSO_{4}^{-}$ or $HSeO_{4}^{-}$
(b) NH₃ or H₂O
(c) PH₃ or HI
(d) NH₃ or PH₃
(e) H₂S or HBr
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Exercises 43
Rank the compounds in each of the following groups in order of increasing acidity or basicity, as indicated, and explain the order you assign.
(a) acidity: NaHSO₃, NaHSeO₃, NaHSO₄
(b) basicity: $BrO_{2}^{-},$ $ClO_{2}^{-},$ $IO_{2}^{-}$
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Exercises 45
The active ingredient formed by aspirin in the body is salicylic acid, C₆H₄OH(CO₂H). The carboxyl group (−CO₂H) acts as a weak acid. The phenol group (an OH group bonded to an aromatic ring) also acts as an acid but a much weaker acid. List, in order of descending concentration, all of the ionic and molecular species present in a 0.001-M aqueous solution of C₆H₄OH(CO₂H).
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Exercises 47
What two common assumptions can simplify calculation of equilibrium concentrations in a solution of a weak acid or base?
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Exercises 48
Which of the following will increase the percent of NH₃ that is converted to the ammonium ion in water?
(a) addition of NaOH
(b) addition of HCl
(c) addition of NH₄Cl
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Exercises 50
What is the effect on the concentrations of $NO_{2}^{-},$ HNO₂, and OH⁻ when the following are added to a solution of KNO₂ in water:
(a) HCl
(b) HNO₂
(c) NaOH
(d) NaCl
(e) KNO₂
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Exercises 52
Why is the hydronium ion concentration in a solution that is 0.10 M in HCl and 0.10 M in HCOOH determined by the concentration of HCl?
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Exercises 54
From the equilibrium concentrations given, calculate K $_{a}$ for each of the weak acids and K $_{b}$ for each of the weak bases.
(a) NH₃: [OH⁻] = 3.1 $\times$ 10⁻³ M;
$[NH_{4}^{+}]$ = 3.1 10⁻³ ;
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Exercises 56
Determine K $_{a}$ for hydrogen sulfate ion, $HSO_{4}^{-} .$ In a 0.10-M solution the acid is 29% ionized.
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Exercises 58
Calculate the ionization constant for each of the following acids or bases from the ionization constant of its conjugate base or conjugate acid:
(a) HTe⁻ (as a base)
(b) $(CH_{3})_{3} NH^{+}$
(c) $HAsO_{4}^{2 -}$ (as a base)
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Exercises 60
Calculate the concentration of all solute species in each of the following solutions of acids or bases. Assume that the ionization of water can be neglected, and show that the change in the initial concentrations can be neglected.
(a) 0.0092 M HClO, a weak acid
(b) 0.0784 M C₆H₅NH₂, a weak base
(c) 0.0810 M HCN, a weak acid
(d) 0.11 M (CH₃)₃N, a weak base
(e) 0.120 M $Fe (H_{2} O)_{6}^{2 +}$ a weak acid, K $_{a}$ = 1.6 10⁻⁷
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Exercises 62
White vinegar is a 5.0% by mass solution of acetic acid in water. If the density of white vinegar is 1.007 g/cm³, what is the pH?
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Exercises 64
Nicotine, C₁₀H₁₄N₂, is a base that will accept two protons (K $_{b 1}$ = 7 $\times$ 10⁻⁷, K $_{b 2}$ = 1.4 $\times$ 10⁻¹¹). What is the concentration of each species present in a 0.050-M solution of nicotine?
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Exercises 66
The pH of a 0.15-M solution of $HSO_{4}^{-}$ is 1.43. Determine K $_{a}$ for $HSO_{4}^{-}$ from these data.
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Exercises 68
The pH of a solution of household ammonia, a 0.950 M solution of NH3, is 11.612. Determine K $_{b}$ for NH₃ from these data.
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Key terms · 5

acid ionization constant (K_a): equilibrium constant for an acid ionization reaction
base ionization constant (K_b): equilibrium constant for a base ionization reaction
leveling effect: observation that acid-base strength of solutes in a given solvent is limited to that of the solvent’s characteristic acid and base species (in water, hydronium and hydroxide ions, respectively)
oxyacid: ternary compound with acidic properties, molecules of which contain a central nonmetallic atom bonded to one or more O atoms, at least one of which is bonded to an ionizable H atom
percent ionization: ratio of the concentration of ionized acid to initial acid concentration expressed as a percentage

Learn 14.3 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 14.3 in the textbook · This section on openstax.org

Relative Strengths of Acids and Bases: practice problems

22 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 27

Explain why the neutralization reaction of a weak acid and a strong base gives a weakly basic solution.

Exercises 29

The odor of vinegar is due to the presence of acetic acid, CH₃CO₂H, a weak acid. List, in order of descending concentration, all of the ionic and molecular species present in a 1-M aqueous solution of this acid.

Exercises 31

Explain why the ionization constant, K $_{a}$ , for H₂SO₄ is larger than the ionization constant for H₂SO₃.

Exercises 33

Gastric juice, the digestive fluid produced in the stomach, contains hydrochloric acid, HCl. Milk of Magnesia, a suspension of solid Mg(OH)₂ in an aqueous medium, is sometimes used to neutralize excess stomach acid. Write a complete balanced equation for the neutralization reaction, and identify the conjugate acid-base pairs.

Exercises 35

What is the ionization constant at 25 °C for the weak acid $CH_{3} NH_{3}^{+},$ the conjugate acid of the weak base CH₃NH₂, K $_{b}$ = 4.4 $\times$ 10⁻⁴.

Exercises 37

Which base, CH₃NH₂ or (CH₃)₂NH, is the stronger base? Which conjugate acid, $(CH_{3})_{2} NH_{2}^{+}$ or $CH_{3} NH_{3}^{+}$ , is the stronger acid?

Exercises 39

Which is the stronger base, (CH₃)₃N or $H_{2} BO_{3}^{-} ?$

Exercises 41

Predict which compound in each of the following pairs of compounds is more acidic and explain your reasoning for each.

(a) $HSO_{4}^{-}$ or $HSeO_{4}^{-}$

(b) NH₃ or H₂O

(d) NH₃ or PH₃

(e) H₂S or HBr

Exercises 43

Rank the compounds in each of the following groups in order of increasing acidity or basicity, as indicated, and explain the order you assign.

(a) acidity: NaHSO₃, NaHSeO₃, NaHSO₄

(b) basicity: $BrO_{2}^{-},$ $ClO_{2}^{-},$ $IO_{2}^{-}$

Exercises 45

The active ingredient formed by aspirin in the body is salicylic acid, C₆H₄OH(CO₂H). The carboxyl group (−CO₂H) acts as a weak acid. The phenol group (an OH group bonded to an aromatic ring) also acts as an acid but a much weaker acid. List, in order of descending concentration, all of the ionic and molecular species present in a 0.001-M aqueous solution of C₆H₄OH(CO₂H).

Exercises 47

What two common assumptions can simplify calculation of equilibrium concentrations in a solution of a weak acid or base?

Exercises 48

Which of the following will increase the percent of NH₃ that is converted to the ammonium ion in water?

(a) addition of NaOH

(b) addition of HCl

Exercises 50

What is the effect on the concentrations of $NO_{2}^{-},$ HNO₂, and OH⁻ when the following are added to a solution of KNO₂ in water:

(a) HCl

(b) HNO₂

(d) NaCl

(e) KNO₂

Exercises 52

Why is the hydronium ion concentration in a solution that is 0.10 M in HCl and 0.10 M in HCOOH determined by the concentration of HCl?

Exercises 54

From the equilibrium concentrations given, calculate K $_{a}$ for each of the weak acids and K $_{b}$ for each of the weak bases.

(a) NH₃: [OH⁻] = 3.1 $\times$ 10⁻³ M;

$[NH_{4}^{+}]$ = 3.1 10⁻³ ;

Exercises 56

Determine K $_{a}$ for hydrogen sulfate ion, $HSO_{4}^{-} .$ In a 0.10-M solution the acid is 29% ionized.

Exercises 58

Calculate the ionization constant for each of the following acids or bases from the ionization constant of its conjugate base or conjugate acid:

(a) HTe⁻ (as a base)

(b) $(CH_{3})_{3} NH^{+}$

Exercises 60

Calculate the concentration of all solute species in each of the following solutions of acids or bases. Assume that the ionization of water can be neglected, and show that the change in the initial concentrations can be neglected.

(a) 0.0092 M HClO, a weak acid

(b) 0.0784 M C₆H₅NH₂, a weak base

(d) 0.11 M (CH₃)₃N, a weak base

(e) 0.120 M $Fe (H_{2} O)_{6}^{2 +}$ a weak acid, K $_{a}$ = 1.6 10⁻⁷

Exercises 62

White vinegar is a 5.0% by mass solution of acetic acid in water. If the density of white vinegar is 1.007 g/cm³, what is the pH?

Exercises 64

Nicotine, C₁₀H₁₄N₂, is a base that will accept two protons (K $_{b 1}$ = 7 $\times$ 10⁻⁷, K $_{b 2}$ = 1.4 $\times$ 10⁻¹¹). What is the concentration of each species present in a 0.050-M solution of nicotine?

Exercises 66

The pH of a 0.15-M solution of $HSO_{4}^{-}$ is 1.43. Determine K $_{a}$ for $HSO_{4}^{-}$ from these data.

Exercises 68

The pH of a solution of household ammonia, a 0.950 M solution of NH3, is 11.612. Determine K $_{b}$ for NH₃ from these data.

Key terms · 5

acid ionization constant (K_a): equilibrium constant for an acid ionization reaction
base ionization constant (K_b): equilibrium constant for a base ionization reaction
leveling effect: observation that acid-base strength of solutes in a given solvent is limited to that of the solvent’s characteristic acid and base species (in water, hydronium and hydroxide ions, respectively)
oxyacid: ternary compound with acidic properties, molecules of which contain a central nonmetallic atom bonded to one or more O atoms, at least one of which is bonded to an ionizable H atom
percent ionization: ratio of the concentration of ionized acid to initial acid concentration expressed as a percentage

Learn 14.3 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 14.3 in the textbook · This section on openstax.org