18.4 Acid-base titrations
1. Sketch the general shapes of graphs of pH against volume for titrations involving strong and weak acids and bases, and explain their important features.
Strong Acid, Strong Base: Titration of HCl with NaOH
Weak Acid, Weak Base: Titration of CH3COOH with NH3
- Change in pH is gradual. No sharp rises or drops.
- pH at the equivalence point is 7.
Weak Acid, Strong Base: Titration of CH3COOH with NaOH
- When pKa = pH, there is equal concentration of acid and its conjugate base.
- Therefore, the half equivalence point is the region where the buffer is most effective.
- For pKa = pH, the volume of strong base added must be half of the weak acid present.
Strong Acid, Weak Base: Titration of HCl with NH3
- The buffer region is most effective (pOH = pKb) when the volume of weak base is double of the strong acid present.