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Buffer Solutions Overview

Jul 15, 2025

Overview

This lecture introduces buffer solutions, their types, methods of preparation (direct and indirect), and how to identify and form buffer solutions using example problems.

Buffer Solution Definition & Properties

  • A buffer solution maintains a stable pH when small amounts of acid, base, or water are added.
  • Buffer solutions can be either acidic or basic (alkaline).

Types of Buffer Solutions

  • Acidic buffers consist of a weak acid and its salt (conjugate base), e.g., CH₃COOH + CH₃COONa.
  • Basic (alkaline) buffers consist of a weak base and its salt (conjugate acid), e.g., NHâ‚„OH + NHâ‚„Cl.

Methods of Preparing Buffer Solutions

  • Direct method: Mix a weak acid with its salt or a weak base with its salt.
  • Indirect method: React an excess of weak acid with strong base, or an excess of weak base with strong acid.
  • Example: Mixing 1 mole CH₃COOH (weak acid) with 0.5 mole KOH (strong base) yields a buffer (CH₃COOH + CH₃COOK).
  • Example: Mixing 1 mole NHâ‚„OH (weak base) with 0.5 mole HCl (strong acid) yields a buffer (NHâ‚„OH + NHâ‚„Cl).

Example Problems & Solutions

  • To identify a buffer, look for a mixture of a weak acid/base and its corresponding salt.
  • In multiple-choice questions, correct buffer pairs are weak acid with its salt (e.g., NHâ‚„OH and NHâ‚„Cl).
  • For buffers prepared by the indirect method, ensure the weak acid/base is in excess after reaction with a strong base/acid.
  • Calculate moles using volume (L) × concentration (M) to confirm excess.

Key Terms & Definitions

  • Buffer Solution — A solution that resists changes in pH when acids or bases are added.
  • Acidic Buffer — Mixture of a weak acid and its conjugate base (salt).
  • Basic Buffer — Mixture of a weak base and its conjugate acid (salt).
  • Direct Method — Making a buffer by mixing a weak acid/base directly with its salt.
  • Indirect Method — Making a buffer by reacting a weak acid/base in excess with a strong base/acid.

Action Items / Next Steps

  • Practice identifying and preparing buffer solutions using given reactants.
  • Review mole calculations for buffer formation.
  • Prepare for related buffer solution problems in upcoming assignments or exams.

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