Lecture Notes on Acids and Bases

Introduction

• Importance of the chapter on acids and bases.
• Will not cover everything exhaustively due to the chapter's detail.
• Focus will be on Grade 12 syllabus, but will review Grade 11 basics where necessary.
• Lessons will be divided into parts.

Theories of Acids and Bases

• Focus on two main theories:
  1. Arrhenius Theory
  2. Brønsted-Lowry Theory

Arrhenius Theory

• Definition of Acids:

  • Acids ionize in water to produce hydronium ions (H₃O⁺).
  • H⁺ and H₃O⁺ are interchangeable.

• Definition of Bases:

  • Bases dissociate in solution to produce hydroxide ions (OH⁻).
  • Acids donate H⁺; bases donate OH⁻.

Brønsted-Lowry Theory

• Definition of Acids:

  • Acids are substances that donate hydronium ions (H⁺) in solution.

• Definition of Bases:

  • Bases are substances that accept hydronium ions (H⁺).
  • The process of donating and accepting protons is called protolysis.

Key Points

• Acid + Base → Salt + Water
• Importance of identifying conjugate acid-base pairs:
  • Conjugate pairs differ only by the presence of one H⁺ ion.

Identifying Conjugate Acid-Base Pairs

1. HCl + H₂O ⇌ H₃O⁺ + Cl⁻
   • Conjugate pairs: HCl/Cl⁻ and H₃O⁺/H₂O
2. NH₃ + H₂O ⇌ NH₄⁺ + OH⁻
   • Conjugate pairs: NH₃/NH₄⁺ and H₂O/OH⁻

Titration

• Purpose: To determine concentration of an unknown acid or base.
• Process:
  1. Prepare a standard solution with known concentration.
  2. React it with the unknown solution until reaching the endpoint (indicated by color change of an indicator).

Example Reactions 1. HCl + NaOH → NaCl + H₂O

• Balanced reaction:
  • Coefficients indicate 1:1 ratio between acid and base.

2. H₂SO₄ + KOH → K₂SO₄ + H₂O
   • Ensure reactions are balanced to determine stoichiometric ratios.

Titration Calculations

• Use the formula:
  [ C_a V_a / C_b V_b = n_a / n_b ]
• Variables:
  • C = concentration
  • V = volume
  • n = number of moles (stoichiometric coefficients)

Example Problem

• Find the concentration of HCl when titrating 25 cm³ of NaOH (0.5 M) with 50 cm³ of unknown HCl concentration.
• Balanced Reaction: HCl + NaOH → NaCl + H₂O
• Stoichiometric Ratios: 1:1
• Solve using the formula:
  • Result: Concentration of HCl = 0.25 M

Another Example Problem

• Titrating 30 cm³ of 0.06 M sulfuric acid with 0.028 M potassium hydroxide.
• Balanced Reaction: KOH + H₂SO₄ → K₂SO₄ + H₂O
• Solve for unknown volume of KOH needed.
• Result: Volume of KOH = 0.129 dm³

Conclusion

• Next lesson will cover the Brønsted-Lowry theory and calculating pH.
• Reminder to subscribe for future lessons.
• Questions and comments are welcomed.