Lecture Notes: Acids and Bases

Introduction to Acids and Bases

• Exploring properties and definitions of acids and bases.
• Properties of Acids:
  • Taste sour.
  • Turn litmus paper red.
  • React with metals to produce hydrogen gas.
• Properties of Bases:
  • Taste bitter.
  • Turn litmus paper blue.
  • Feel slippery (common in cleaning materials).

Definitions of Acids and Bases

Arrhenius Definition

• Acids produce hydrogen ions (H+) in water.
• Bases produce hydroxide ions (OH-) in water.
• Neutralization Reaction:
  • Hydrogen ions from acids react with hydroxide ions from bases to produce water.
• Limitation:
  • Some bases don’t contain OH-.

Bronsted-Lowry Definition

• Acids are proton (H+) donors.
• Bases are proton acceptors.
• Proton Exchange:
  • Acids donate protons, bases accept them.
• Example: NH3 (ammonia) acts as a base by accepting a proton from water.

Conjugate Acid-Base Pairs

• In reactions, there are two acids and two bases:
  • Conjugate Acid: Formed when a base gains a proton.
  • Conjugate Base: Formed when an acid loses a proton.
• Example Reactions:
  • HCl + H2O → Cl- + H3O+
  • NH3 + H2O → NH4+ + OH-
  • Conjugate pairs: HCl/Cl- and H2O/H3O+

Characteristics of Acids and Bases

• Acids turn litmus red and produce hydrogen gas.
• Bases neutralize acids.
• Hydronium Ion (H3O+):
  • Represents the hydrated form of a proton (H+).

Amphiprotic Substances

• Substances that can both donate and accept a proton.
• Example: Water (H2O) can become H3O+ or OH-.

Net Ionic Equations

• Bronsted-Lowry Acid: Species that lose a proton.
• Bronsted-Lowry Base: Species that accept a proton.
• Examples:
  • H2CO3 → HCO3- (loses H+)
  • HSO4- → SO4 2- (loses H+)

Amphiprotic Examples

• OH-: Can gain a proton to become H2O or lose a proton.
• HSO4-: Can gain a proton to become H2SO4 or lose a proton to become SO4 2-.

Conclusion

• Understanding acid-base reactions involves recognizing proton donors and acceptors and identifying conjugate acid-base pairs.
• Many substances can act as either acids or bases, depending on the reaction.