Initial Setup: Measure a fixed volume of acid (e.g., ) into a beaker and place it on a magnetic stirrer to ensure constant homogenization of the solution.
Incremental Addition: Add the titrant from a burette in large portions (e.g., ) initially, then switch to much smaller increments (e.g., or drops) as the pH begins to rise rapidly.
Data Collection: Record the pH after each addition only once the reading on the pH probe has stabilized to ensure accuracy.
Post-Equivalence: Once the pH rise slows down again, return to larger volume increments until a sufficient excess of titrant has been added to define the final plateau.
| Combination | Starting pH | Equivalence pH | Curve Shape |
|---|---|---|---|
| Strong Acid + Strong Base | Very Low (~1) | Exactly 7 | Long vertical section |
| Weak Acid + Strong Base | Moderate (~3-4) | > 7 | Short vertical section |
| Strong Acid + Weak Base | Very Low (~1) | < 7 | Short vertical section |
| Weak Acid + Weak Base | Moderate (~3-4) | ~7 | No clear vertical section |
Locating Equivalence: Always identify the equivalence point as the midpoint of the vertical region of the curve, not just where the pH is 7.
Precision in Plotting: Ensure that you have enough data points in the vertical region; missing these points makes it impossible to accurately determine the equivalence volume.
Units and Labels: When drawing graphs, always include units for volume (usually ) and ensure the pH axis ranges from 0 to 14.
Sanity Check: Verify that the starting pH matches the strength of the acid in the beaker (e.g., a pH of 1 for ).
Stirring Speed: Stirring too vigorously can introduce air bubbles around the pH probe, leading to erratic and unsteady readings.
Probe Stabilization: Failing to wait for the pH meter to settle before recording a value is a common source of experimental error.
Calibration Neglect: pH probes drift over time; they must be calibrated using a two-point or three-point method with standard buffer solutions before the experiment begins.
