Lecture on Acids, Bases, and pH

Overview

• Focus on acids, bases, and pH
• Will concentrate mainly on acids and pH
• Additional videos will cover bases and the dissociation of water

Definitions

Bronsted-Lowry Acids and Bases

• Acid: Proton donor
• Base: Proton acceptor
• Examples:
  • NH₃ + H⁺ → NH₄⁺ (NH₃ acts as a base)
  • HCl + H₂O → H₃O⁺ + Cl⁻ (HCl acts as an acid, H₂O as a base)
• Importance of understanding proton transfer to classify acids and bases

pH Scale

• pH is a measure of hydrogen ion concentration
• pH Scale: Logarithmic, ranges from 0 to 14 in common use, but can be negative or greater than 14
  • Strong acids: Low pH
  • Strong bases/alkalis: High pH
  • Neutral: pH of 7

Calculating pH

• Formula: pH = -log [H⁺]
  • Square brackets denote concentration in moles per decimeter cubed
  • Example: [H⁺] = 1 mol/dm³ → pH = 0
• Reverse calculation: [H⁺] = 10^-pH

Acid and pH Calculations

• Strong Acids: Fully dissociate in water
• Example Calculations:
  • 0.15 M HCl:
    • H⁺ concentration = 0.15 M
    • pH = -log(0.15) = 0.82
  • 2.64 M HNO₃:
    • H⁺ concentration = 2.64 M
    • pH = -log(2.64) = -0.42

Special Cases: Diprotic Acids

• Example: H₂SO₄ (Sulfuric Acid)
  • Dissociates to produce 2 H⁺ per molecule
  • 0.315 M H₂SO₄:
    • H⁺ concentration = 0.315 * 2 = 0.63 M
    • pH = -log(0.63) = 0.20*

Exam Tips

• Always calculate pH to two decimal places, rounding correctly
• Understand the concept of dissociation and its impact on ion concentration
• Practice problems to become comfortable with identifying acids and bases based on proton transfer

Conclusion

• Understanding of acids, bases, and pH forms the basis for more complex topics in chemistry
• The lecture is an introduction, with more detailed exploration in subsequent videos

Feel free to download these notes as a reference. Good luck with your studies!