Introduction to the Working Principle of a pH Meter
A pH meter is used to measure the pH value of a solution using the potentiometric method. Therefore, in addition to measuring the pH value of the solution, the working mode of a pH meter can also measure the electromotive force of the battery. PH, in Latin, is the abbreviation for Pondus hydrogeni, which is the activity of hydrogen ions in a substance. PH is the negative logarithm of the concentration of hydrogen ions.
The main measuring components of a pH meter are a glass electrode and a reference electrode. The glass electrode is sensitive to pH, while the potential of the reference electrode is stable. Putting the two electrodes of the pH meter together into the same solution forms a primary cell, and the potential of this primary cell is the algebraic sum of the potentials of the glass electrode and the reference electrode.
The reference electrode potential of a pH meter is stable, so under stable temperature conditions, the potential change of the original battery composed of solution and electrode is only related to the potential of the glass electrode, which depends on the pH value of the solution being measured. Therefore, by measuring the potential change, the pH value of the pH solution can be obtained.
Preparation work before using a pH meter
1. Before using the pH meter, clean the electrode with distilled water and be careful not to break the glass electrode.
2. Prepare to place the NAOH and HCL solutions for adjustment next to the pH meter on the platform.
3. Take out the pH solution (pH=7.0) from the refrigerator and place it on the platform.
4. Open the pH meter, set the pH value, press the ^>key to select the pH and CAL options, select the CAL option, adjust and insert it into the pH solution (pH=7.0), press the "" key to select the data value to 7.0, and a small eight fork will appear.
5. Insert the glass electrode into the solution to be tested, then place another electrode and stir the liquid surface appropriately (note: do not crush the glass electrode).
6. When using the electronic unit of a pH meter, attention must be paid to the protection of the circuit. When not measuring the pH value, the input of the pH meter should be short circuited to avoid damage to the pH meter.
7. The glass electrode socket of the pH meter must be kept clean, tidy, and dry, and must not come into contact with harmful gases such as salt spray and acid spray. At the same time, it is strictly prohibited for the glass electrode socket to be contaminated with any aqueous solution to avoid high input impedance of the pH meter.
8. Be careful when adding solutions such as NaOH and HCL before reaching the pH value you need (depending on the adjustment range, different concentrations of adjustment solutions can be selected, with fast addition when the concentration is low and slow addition when the concentration is high).
9. Be careful not to exceed the required capacity when adding liquid.
