Tech Note 315 Detail

pH sensor reads that pure water is acidic.

Affected Products:

PS-2102 PASPORT pH Sensor
CI-6507A pH Sensor
PS-2169 PASPORT Water Quality Sensor

Problem/Symptom:
The calibrated pH probe reads that pure water is acidic.

PASCO Solution:

This is normal: By definition, pure water has a pH of 7 because it has equal numbers of H+ and OH- ions; however, any "pure" water that has been exposed to the atmosphere will have a pH of ~ 6 because CO2 will dissolve in the water and create carbonic acid.

Because the pH of pure water is unpredictable and easily changed by the slightest amount of contamination, it should never be used as a calibration point. Use only bufferered solutions for calibration.

Creation Date: 02/13/2002
Last Modified: 06/12/2012
Mod Summary: