pH is a measurable parameter between the values of 0 and 14, provided the concentration of the solution does not exceed 1M. Solutions with a pH<7 are acidic, whereas those with a pH>7 are alkaline. A PH METER is a device that measures the changes in the activity of hydrogen ions in a solution.
pH meters are electronic devices comprised of a special measuring probe (a glass electrode or, an ion-selective field-effect transistor (ISFET), in specialized cases), attached to an electronic meter that displays the decimal pH reading. The Automatic Calibration PH Meter must be calibrated prior to use against buffer solutions of known hydrogen ion activity.
The standard methodology for measuring pH
Combined PH meters consist of a glass electrode made of a specialty glass membrane that is sealed at the end forming a bulb. Inside the glass is an internal standard acidity solution, usually 0.1 M HCl, along with an internal reference electrode, REin (typically an Ag/AgCl wire electrode). This solution is called the reference solution of known pH, 7.
A second electrode REext is placed in an external tube immersed in KCl. This external tube forms a concentric enclosure around the first enclosed glass tube containing the 0.1 M HCl (the internal tube).
The external tube is made of pH-sensitive glass and is in contact with the test solution through an opening called a porous diaphragm. The inclusion of a reference electrode encased by the internal tube is necessary as its pH is known and can be compared to a test solution so that its pH value can be determined. This set-up is called a combination pH electrode.
Operation of pH meter
The 3 in 1 PH Meter operates like a voltmeter. The pair of electrodes in the combinatorial set-up can measure small changes in voltage (also called potential difference) in the order of millivolts. Changes in potentials are caused by the loss of electrons that correspond with the loss of H+.