Soil and Water Chemistry (1+2)

Determination of pH by electrometric method

Introduction: Measurement of pH is one of the most important and frequently used test in water chemistry; practically every phase of water supply and waste water treatment. pH is used in alkalinity and CO₂ measurement and many other acid-base equilibrium.

Principle:

The basic principle of the electrometric pH measurement is determination of the activity of the hydrogen ion by potentiometric measurement using a standard hydrogen electrode and a reference electrode.

Apparatus:

pH meter consisting of potentiometer, a glass electrode, a reference electrode and a temperature-compensating device.
Glass electrode: The sensor electrode is bulb of special glass containing a fixed concentration of HCl and a buffered chloride solution in contact with an internal reference electrode.

Procedure:

Before use, remove electrode from storage solution, rinse, and blot, dry with a soft tissue paper.
Calibrate the instrument with standard buffer solution. [Ex: KCl solution of pH 7.0]

Once the instrument is calibrated remove the electrode from standard solution; rinse, blot and dry.
Dip the electrode in the sample whose pH has to be measured.
Stir the sample to ensure homogeneity and to minimize CO₂ entrainment.
Note down the reading (pH) from the pH meter.