pH and pKa

  • If you know the pH and pKa on an environment, you can know the ratio of [A-]/[HA]

          ○ If the ratio of [A-]/[HA] is > 1 → [HA] < [A-] & pH > pKa,

          ○ If the ratio of [A-]/[HA] is < 1 → [HA] > [A-] & pH < pKa

Acid-Base Indicators

  • Indicators are used in titrations to indicate when we have passed the equivalence point

               ○ Are weak acids that change color when they become conj. bases

  • Indicators have a “useful range” → have kA and pKa values
  • Useful indicator range =   

               ○ Best indicator to choose for a titration will be the one whose useful range includes or is closest to the pH at equivalence → color change will occur closest to eq. point