Introduction to the structure and principle of PH meter
1. A reference electrode;
2. A glass electrode whose potential depends on the pH of the surrounding solution;
3. A galvanometer capable of measuring small potential differences in a circuit of great resistance.
The following are the main functions of each component:
1. The basic function of the reference electrode is to maintain a constant potential as a control for measuring various deviation potentials. The silver-silver oxide electrode is currently the most commonly used reference electrode in pH.
2. The function of the glass electrode is to establish a potential difference that responds to changes in the hydrogen ion activity of the solution being measured. Put the pH-sensitive electrode and the reference electrode in the same solution to form a primary battery, and the potential of the battery is the algebraic sum of the potential of the glass electrode and the reference electrode. E battery = E reference + E glass, if the temperature is constant, the potential of this battery changes with the pH of the solution to be measured, and it is difficult to measure the potential generated by the battery in the pH meter because its electromotive force is very small and the circuit The impedance is very large, 1-100MΩ; therefore, the signal must be amplified enough to drive a standard millivoltmeter or milliamperemeter.
3. The function of the ammeter is to amplify the potential of the primary battery several times. The amplified signal is displayed by the ammeter. The degree of deflection of the pointer of the ammeter indicates the strength of the signal it pushes. For the needs of use, the dial of the pH ammeter is engraved with The corresponding pH value; while the digital pH meter directly displays the pH value in numbers.
How a pH Meter Works
The pH meter uses potentiometric method to measure the pH value of the solution. Therefore, the working method of the pH meter can not only measure the pH value of the solution, but also measure the electromotive force of the battery. In Latin, PH is the abbreviation of Pondus hydrogenii, which is the activity of hydrogen ions in the substance, and the pH value is the negative number of the logarithm of the concentration of hydrogen ions.
The main measuring parts of the pH meter are the glass electrode and the reference electrode, the glass electrode is sensitive to pH, and the potential of the reference electrode is stable. Put the two electrodes of the pH meter into the same solution together to form a primary battery, and the potential of the primary battery is the algebraic sum of the potentials of the glass electrode and the reference electrode.
The potential of the reference electrode of the pH meter is stable, so when the temperature remains stable, the potential change of the primary battery composed of the solution and the electrode is only related to the potential of the glass electrode, and the potential of the glass electrode depends on the pH of the solution to be measured Therefore, by measuring the change of the potential, the pH value of the pH solution can be obtained.
