Analytical chemistryLesson 1 of 2 in the course Acid-Base Equilibria

Buffer Composition, Capacity, and Henderson–Hasselbalch Applications

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Buffers help keep a solution’s pH relatively stable when small amounts of acid or base are added. This lesson introduces buffer composition and explains how its two components respond to added acid and base.

A buffer solution contains appreciable amounts of a weak acid and its conjugate base, or a weak base and its conjugate acid. These partners can react with added acid or base, limiting the resulting pH change.

All flashcards

What is a buffer solution?
A solution containing appreciable amounts of a weak acid-base conjugate pair that resists pH changes when modest amounts of strong acid or base are added.
What is the conjugate pair in an acetic acid buffer?
Acetic acid, CH₃COOH, and acetate, CH₃COO⁻. Sodium acetate is a soluble source of acetate ions.
How does an acetate buffer respond to added hydronium?
Acetate ions consume added H₃O⁺ and form acetic acid and water, reducing the impact of the acid on pH.
How does an acetic acid buffer respond to added hydroxide?
Acetic acid reacts with OH⁻ to form acetate and water, so some of the added base is neutralized.
Give an example of a buffer made from a weak base and its salt.
Ammonia and ammonium chloride: NH₃ is the weak base, and NH₄Cl supplies its conjugate acid, NH₄⁺.

Quiz questions

  1. Two buffers have the same acid-to-conjugate-base ratio, but one contains higher concentrations of both components. Which statement best describes the more concentrated buffer?Answer: It generally has greater capacity to absorb added acid or base.
  2. Which equation relates the pH of a weak-acid buffer to its conjugate-base-to-acid ratio?Answer: pH=pKa+log⁡([A−]/[HA])pH=pK_a+\log([A^-]/[HA])
  3. In a weak-acid buffer, what is the relationship between pH and pKapK_a when the acid and conjugate-base concentrations are equal?Answer: The pH equals pKapK_a.
  4. Which buffer components are generally suitable for a target pH above 7?Answer: A weak base and its conjugate acid.
  5. How does faster breathing affect the carbon dioxide/carbonic acid system in blood?Answer: It removes more CO₂ and shifts the system toward lower hydronium concentration.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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