amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit)

mixture of appreciable amounts of a weak acid-base pair. The pH of a buffer resists change when small amounts of acid or base are added

Henderson-Hasselbalch equation

logarithmic version of the acid ionization constant expression, conveniently formatted for calculating the pH of buffer solutions

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Chemistry 2e · 14.6 Buffers

Buffers: practice problems

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

Exercises 78
Explain why the pH does not change significantly when a small amount of an acid or a base is added to a solution that contains equal amounts of the acid H₃PO₄ and a salt of its conjugate base NaH₂PO₄.
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Exercises 80
What is [H₃O⁺] in a solution of 0.25 M CH₃CO₂H and 0.030 M NaCH₃CO₂?
$CH_{3} CO_{2} H (a q) + H_{2} O (l) ⇌ H_{3} O^{+} (a q) + CH_{3} CO_{2}^{-} (a q) K_{a} = 1.8 \times 10^{- 5}$
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Exercises 82
What is [OH⁻] in a solution of 0.125 M CH₃NH₂ and 0.130 M CH₃NH₃Cl?
$CH_{3} NH_{2} (a q) + H_{2} O (l) ⇌ CH_{3} NH_{3}^{+} (a q) + OH^{-} (a q) K_{b} = 4.4 \times 10^{- 4}$
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Exercises 84
What is the effect on the concentration of acetic acid, hydronium ion, and acetate ion when the following are added to an acidic buffer solution of equal concentrations of acetic acid and sodium acetate:
(a) HCl
(b) KCH₃CO₂
(c) NaCl
(d) KOH
(e) CH₃CO₂H
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Exercises 86
What will be the pH of a buffer solution prepared from 0.20 mol NH₃, 0.40 mol NH₄NO₃, and just enough water to give 1.00 L of solution?
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Exercises 88
How much solid NaCH₃CO₂•3H₂O must be added to 0.300 L of a 0.50-M acetic acid solution to give a buffer with a pH of 5.00? (Hint: Assume a negligible change in volume as the solid is added.)
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Exercises 90
A buffer solution is prepared from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate. Use 1.80 $\times$ 10⁻⁵ as K $_{a}$ for acetic acid.
(a) What is the pH of the solution?
(b) Is the solution acidic or basic?
(c) What is the pH of a solution that results when 3.00 mL of 0.034 M HCl is added to 0.200 L of the original buffer?
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Key terms · 3

buffer capacity: amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit)
buffer: mixture of appreciable amounts of a weak acid-base pair. The pH of a buffer resists change when small amounts of acid or base are added
Henderson-Hasselbalch equation: logarithmic version of the acid ionization constant expression, conveniently formatted for calculating the pH of buffer solutions

Learn 14.6 on the whiteboard

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

Read 14.6 in the textbook · This section on openstax.org

Buffers: practice problems

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

Exercises 78

Explain why the pH does not change significantly when a small amount of an acid or a base is added to a solution that contains equal amounts of the acid H₃PO₄ and a salt of its conjugate base NaH₂PO₄.

Exercises 80

What is [H₃O⁺] in a solution of 0.25 M CH₃CO₂H and 0.030 M NaCH₃CO₂?

$CH_{3} CO_{2} H (a q) + H_{2} O (l) ⇌ H_{3} O^{+} (a q) + CH_{3} CO_{2}^{-} (a q) K_{a} = 1.8 \times 10^{- 5}$

Exercises 82

What is [OH⁻] in a solution of 0.125 M CH₃NH₂ and 0.130 M CH₃NH₃Cl?

$CH_{3} NH_{2} (a q) + H_{2} O (l) ⇌ CH_{3} NH_{3}^{+} (a q) + OH^{-} (a q) K_{b} = 4.4 \times 10^{- 4}$

Exercises 84

What is the effect on the concentration of acetic acid, hydronium ion, and acetate ion when the following are added to an acidic buffer solution of equal concentrations of acetic acid and sodium acetate:

(a) HCl

(b) KCH₃CO₂

(d) KOH

(e) CH₃CO₂H

Exercises 86

What will be the pH of a buffer solution prepared from 0.20 mol NH₃, 0.40 mol NH₄NO₃, and just enough water to give 1.00 L of solution?

Exercises 88

How much solid NaCH₃CO₂•3H₂O must be added to 0.300 L of a 0.50-M acetic acid solution to give a buffer with a pH of 5.00? (Hint: Assume a negligible change in volume as the solid is added.)

Exercises 90

A buffer solution is prepared from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate. Use 1.80 $\times$ 10⁻⁵ as K $_{a}$ for acetic acid.

(a) What is the pH of the solution?

(b) Is the solution acidic or basic?

Key terms · 3

buffer capacity: amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit)
buffer: mixture of appreciable amounts of a weak acid-base pair. The pH of a buffer resists change when small amounts of acid or base are added
Henderson-Hasselbalch equation: logarithmic version of the acid ionization constant expression, conveniently formatted for calculating the pH of buffer solutions

Learn 14.6 on the whiteboard

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

Read 14.6 in the textbook · This section on openstax.org