Reading a pH curve
A pH curve shows how the pH changes as one solution is progressively added to another during an acid–base titration.
When base is added to an acid, the curve rises. Useful information can be obtained from its position and shape:
- The starting point gives the initial pH.
- The steep region shows where a small addition of titrant produces a large change in pH.
- The midpoint of this rapid change identifies the equivalence point.
- Its x-coordinate gives the equivalence volume.
- Its y-coordinate gives the pH at equivalence.
If acid is added to a base instead, the curve falls rather than rises; the same features can still be identified.
Exam Tip: Locate equivalence at the midpoint of the steep part of the curve rather than assuming that it must occur at pH 7.