If a calibrated pH probe shows a slow response, what is a likely cause?

• A. The probe is not connected
• B. The bulb is coated
• C. The sensor is malfunctioning
• D. Insufficient calibration solution

Answer: (B)

A slow response from a calibrated pH probe is often indicative of a coating or buildup on the bulb of the probe. The pH probe works by measuring the hydrogen ion concentration in the solution, and any obstruction on the bulb can hinder its ability to accurately detect this concentration. Substances such as oils, dirt, or biological growth can create a barrier that affects the probe's reaction time to changes in pH.

In contrast, if a probe is not connected, it would not provide any reading at all rather than a slow one. A malfunctioning sensor would typically show erratic readings or fail to provide stable data rather than simply responding slowly. Finally, insufficient calibration solution could lead to inaccurate readings post-calibration, but it would not directly affect the responsiveness of a properly calibrated probe. Thus, a coating on the bulb is a common and plausible reason for a slow response in a pH probe.