Notes on Buffer Solutions

Introduction to Buffer Solutions

• Definition and purpose of buffer solutions
• Example scenario with a beaker and universal indicator
• Initial pH of solution is neutral (~pH 7)

Impact of Adding Acid and Alkali

• Adding H+ (acid) results in a color change to red (indicating acidity)
• Adding OH- (alkali) results in a color change to blue (indicating alkalinity)

Characteristics of Buffer Solutions

• Adding a small amount of acid (H+) or alkali (OH-) has minimal effect on pH
• Buffers can resist changes in pH when acids or alkalis are added
• However, effectiveness is limited to small amounts; excessive addition of acid or alkali will overwhelm the buffer

Components of a Buffer Solution

1. Weak Acid (HA)

   • Represented as HA, where H is hydrogen and A is the rest of the acid compound (e.g. ethanoic acid)
   • Partially dissociates to form H+ and A- (conjugate base)
   • Equilibrium favors the undissociated HA, keeping pH relatively stable

2. Conjugate Base (A-)

   • Derived from the weak acid
   • Reacts with added alkali (OH-) to produce water and the weak acid, maintaining neutrality

Mechanism of Action

• Reaction with Alkali:

  • Weak acid (HA) reacts with alkali (OH-) to form water and conjugate base (A-)
  • This reaction helps to neutralize the alkali, preventing significant pH change

• Reaction with Acid:

  • Added H+ (acid) could react with A- (conjugate base) to form HA again
  • To ensure sufficient A- is available, a soluble salt of the weak acid (e.g. NaA) must be present
  • NaA fully dissociates to Na+ and A- providing enough conjugate base to react with incoming H+

Summary of Buffer Functionality

• Buffers can maintain pH within a narrow range
• Key components:
  • Weak Acid (HA)
  • Salt of Weak Acid (e.g. NaA)
• Effectiveness diminishes with excessive acid or alkali additions

Conclusion

• Understanding the role of weak acids and their salts is essential in buffering systems
• Encouragement to engage with the video for further learning and understanding.