PIPC1 Topic 6: Introduction to Ionic Equilibrium

Jul 25, 2024

Topic 6: Introduction to Ionic Equilibrium

What is Ionic Equilibrium?

  • Definition: A chemical balance established between molecules and their ions in a solution.
  • Example: Formic acid (HCOOH) in water
    • Partially dissociates into hydrogen ions (H⁺) and formic ions (HCOO⁻)
    • Major substances in solution: Water (H₂O), formic acid, H⁺ ions, and HCOO⁻ ions
    • This balance is termed as ionic equilibrium.

Acids and Bases

Theories of Acids and Bases

  1. Arrhenius Acid and Base Theory
  2. Brønsted-Lowry Acid and Base Theory
    • In PIPC1, focus is on this theory.
  3. Lewis Acid and Base Theory
    • Covered in higher studies.

Brønsted-Lowry Acid and Base Theory

  • Acid: Proton donor (H⁺ ions)
    • Monoprotic acid: Donates one proton (e.g., HCl)
    • Polyprotic acid: Donates more than one proton (e.g., H₂SO₄)
  • Methane (CH₄): Not an acid because it cannot donate a proton.

General Properties of Acids

  1. Sour taste (e.g., phosphoric acid in coke, citric acid in lemon juice).
  2. pH value less than 7.
  3. Turns blue litmus paper red.
  4. Reacts with bases to form salt and water (neutralization reaction): HCl + NaOH → NaCl + H₂O

Strong Acids vs. Weak Acids

  • Strong Acids: Fully dissociate in water (e.g., HCl)
    • Dissociation example: 1M HCl → 1M H⁺ + 1M Cl⁻
    • One-directional reaction arrow.
  • Weak Acids: Partially dissociate in water (e.g., acetic acid, CH₃COOH)
    • Dissociation example: 1M CH₃COOH → 0.99M CH₃COOH + 0.01M H⁺ + 0.01M CH₃COO⁻
    • Half-arrows indicate reversible reaction.

Brønsted-Lowry Base

  • Base: Proton acceptor (e.g., NH₃)
    • Strong Bases: Fully dissociate in water (e.g., NaOH)
    • Weak Bases: Partially dissociate in water (e.g., NH₃ → NH₄⁺ + OH⁻)

General Properties of Bases

  1. Bitter taste (e.g., lime water, Ca(OH)₂).
  2. Slippery or soapy feel.
  3. pH value greater than 7.
  4. Turns red litmus paper blue.
  5. React with acids to form salt and water.

Memorization List for PIPC1

  1. Strong Acids: (7)
  • Hydrochloric Acid (HCl)
  • Nitric Acid (HNO₃)
  • Sulfuric Acid (H₂SO₄)
  • Hydroiodic Acid (HI)
  • Hydrobromic Acid (HBr)
  • Chloric Acid (HClO₃)
  • Perchloric Acid (HClO₄)
  1. Weak Acids: (Organic Acids)
  • Formic Acid (HCOOH)
  • Acetic Acid (CH₃COOH)
  • Benzoic Acid (C₆H₅COOH)
  1. Strong Bases: (Group 1 and 2 metal hydroxides)
  • Lithium Hydroxide (LiOH)
  • Sodium Hydroxide (NaOH)
  • Potassium Hydroxide (KOH)
  • Magnesium Hydroxide (Mg(OH)₂)
  • Calcium Hydroxide (Ca(OH)₂)
  1. Weak Bases:
  • Ammonia (NH₃)