Lecture Notes: Acid-Base Chemistry and Proton Transfer Reactions

Introduction

• Importance of understanding acid-base chemistry for:
  • Biochemistry within human bodies
  • Health of aquatic systems
  • Chemistry of the air
• Acid-base chemistry described as proton transfer reactions.
• Hydrogen ion (H⁺) acts as a lone proton.
• Focus on the nature of proton transfer in acid-base behavior.

Theories of Acids and Bases

Arrhenius Theory

• Sante Arrhenius's definition:
  • Acids release hydrogen ions (H⁺) in solution.
  • Bases release hydroxide ions (OH⁻) in solution.
• Limitations: Does not cover all substances influencing acid-base properties.

Brønsted-Lowry Theory

• Developed by Johannes Brønsted and Martin Lowry.
• Defines acids as proton donors and bases as proton acceptors.
• Acids and bases come in pairs (conjugate acid-base pairs).
• Proton transfer alters concentrations of H⁺ and OH⁻ ions.

Examples of Acid-Base Reactions

Hydrochloric Acid (HCl)

• HCl donates a proton to water (H₂O), forming hydronium ion (H₃O⁺).
• Conjugate acid-base pair:
  • HCl and chloride ion (Cl⁻).
  • Water (H₂O) and hydronium ion (H₃O⁺).

Acetic Acid (CH₃COOH)

• Donates a proton to water, forming acetate ion (CH₃COO⁻) and hydronium ion (H₃O⁺).
• Conjugate acid-base pair:
  • Acetic acid and acetate ion.
  • Water and hydronium ion.

Ammonia (NH₃)

• Accepts a proton from water, forming ammonium ion (NH₄⁺).
• Water acts as a proton donor forming hydroxide ion (OH⁻).
• Conjugate acid-base pair:
  • Ammonia and ammonium ion.
  • Water and hydroxide ion.

Water's Role in Acid-Base Chemistry

• Can act as both acid (proton donor) and base (proton acceptor).
• Water auto-ionization:
  • Responsible for pH scale.
  • KW (ionization constant for water) = 1 * 10⁻¹⁴ at 25°C.
  • [H₃O⁺] = [OH⁻] = 1 * 10⁻⁷ M at 25°C.

Impact of Temperature

• Equilibrium constants change with temperature.
• KW increases with increasing temperature.
• Hydronium and hydroxide concentrations vary with temperature.

Conclusion

• Brønsted-Lowry Theory:
  • Acids like HCl are proton donors.
  • Bases like NH₃ are proton acceptors.
• Conjugate acid-base pairs differ by one proton.
• Water's auto-ionization is crucial for understanding pH.

Future Topics

• Detailed pH calculations to be covered in a future video.

These notes outline the key concepts and examples discussed in the lecture on acid-base chemistry, focusing on proton transfer reactions and the Brønsted-Lowry theory. Understanding these concepts is essential for further exploration into pH calculations and the behavior of acids and bases in various environments.