This section covers calibrating a pH probe with buffer solutions before collecting titration data.
Why calibrate?
A pH probe should be calibrated before it is used to construct a titration curve. Calibration checks the meter against solutions whose pH values are already known and helps account for loss of accuracy during storage.
A two-point calibration can use buffer solutions at pH 4 and pH 9.
1
pH 4 buffer
Place the probe in pH 4 buffer and calibrate the meter so that its reading is 4.0.
2
pH 9 check
Wash the probe with distilled water, place it in pH 9 buffer and check that the meter reads 9.0.
Maintain a constant temperature where possible to improve the accuracy of the pH measurements.
Exam Tip: When describing calibration, include the known buffer values, adjustment using the first buffer and the distilled-water rinse before checking the second buffer.