Skip to main content

pH and pKa

Understanding pH and pKa is essential for analyzing acid-base behavior in aqueous solutions.

pH​

  • Definition: pH measures the hydrogen ion concentration ([H⁺]) in a solution.
  • Formula:
    pH = –log₁₀[H⁺]
  • Scale:
    • pH < 7 → acidic
    • pH = 7 → neutral
    • pH > 7 → basic

pKa​

  • Definition: pKa is the negative logarithm of the acid dissociation constant (Ka).
  • Formula:
    pKa = –log₁₀Ka
  • Interpretation:
    • Lower pKa → stronger acid
    • Higher pKa → weaker acid

Relationship Between pH and pKa​

  • Henderson-Hasselbalch Equation:
    pH = pKa + log([A⁻]/[HA])
    • [A⁻] = conjugate base concentration
    • [HA] = acid concentration
  • This equation helps calculate pH in buffer solutions and predict acid/base behavior.

Importance​

  • Knowing pH and pKa allows chemists to:
    • Predict reaction direction
    • Understand buffer capacity
    • Design controlled chemical reactions

Have Questions?​

If you have any questions, or are looking for more resources, you can join our Discord Server