Week 9: Acid -Base Equilibrium (Part 1)

What does equilibrium mean in acid-base reactions?

It’s when the forward and reverse reactions happen at the same rate, creating a balance between reactants and products.

Ka and Kb – What Do They Mean?

• Ka (Acid Dissociation Constant): Measures how much an acid dissociates into H⁺. K
  a
  
  =
  [
  H
  +
  
  ]
  [
  A
  −
  
  ]
  
  [
  H
  A
  ]
  
  
  
  K_a = \frac{[H⁺][A⁻]}{[HA]}
  
  
  Ka =[HA][H+][A−]

  • Large Ka → Strong acid (completely dissociates).

  • Small Ka → Weak acid (partially dissociates).

• Kb (Base Dissociation Constant): Measures how much a base accepts H⁺.

🔹 Think of Ka & Kb like “strength meters” for acids & bases!

pKa and pKb – Why Do They Matter?

• pKa = -log(Ka)

• pKb = -log(Kb)

• Lower pKa = Stronger Acid

• Lower pKb = Stronger Base

🔹 Easier way to think about it:

• Ka tells you “how much” an acid dissociates.

• pKa makes it easier to compare acid strength (lower = stronger).

If an acid has a low pKa, is it strong or weak?

Strong! Low pKa means the acid dissociates more, making it stronger.