The acidity meter measures the pH value by inserting a pair of working electrodes into the solution to be tested (one is a reference electrode with a known and constant electrode potential, and the other is an electrode whose potential changes with the ion concentration of the solution to be tested. Indicating electrode) constitutes a primary battery, and connected to a precision potentiometer, the electromotive force of the battery can be measured. Since the pH value of the solution to be tested is different, the electromotive force generated is also different . Therefore, the pH value of the solution to be tested can be measured by measuring the electromotive force of the solution with an acidity meter.
In order to save the calculation procedure of converting the electromotive force into a pH value, the measured electromotive force of the battery is usually expressed directly on the electric dial with a pH scale value. At the same time, the instrument is also equipped with a positioning regulator. When measuring, use the pH standard buffer solution first, and make the pointer on the instrument just point to the pH value of the standard solution by positioning the regulator. In this way, when measuring an unknown solution, the pointer directly indicates the pH value of the solution to be tested. Usually the former step is called calibration, and the latter step is called measurement.
The E-201-C9 composite electrode used in the pHS--3B instrument is composed glass electrode is used as a measuring electrode, and the silver-silver chloride electrode is used as a reference electrode. When the concentration of hydrogen ions in the test solution changes , the electromotive force between the glass electrode and the silver-silver chloride electrode also changes accordingly, and the electromotive force change relationship conforms to the following
formula:
It can be seen from the above formula that the change of the electromotive force of the compound electrode is proportional to the change of the pH value of the solution to be measured.
After flushing the solution standard, the pH value of the solution can be measured.
