Introduction to common electrodes used in acidometers (ph meters)
Introduction to Electrodes Used in Acidometers (ph Meters)
Acidity meter is mainly through the electrode and the solution to generate microvoltage, so what kind of electrode is used is very important to the size of the acidity value. The electrodes that we commonly use for acidity measurement are as follows.
(1) Hydrogen electrode: The principle of hydrogen electrode is quite similar to that of metal electrode. However, hydrogen is a gas and cannot be used directly as an electrode. Instead, a platinum electrode coated with platinum black is needed to adsorb the hydrogen to act as a metal electrode. Its main advantage is that it is accurate and can be used to measure a wide pH range. However, this electrode in the redox process, the generation of other oxidation or reduction of substances, will cause measurement errors, the operation is not convenient, so this electrode is generally only used as a standard electrode, the actual measurement is rarely used.
(2) Quinone Hydroquinone Electrode: It is an inert metal platinum or gold immersed in a quinone hydroquinone saturated solution, and is composed of a potential equilibrium established by using quinone hydroquinone on an inert electrode. The advantages of the quinone-hydroquinone electrode are fast potential stabilisation and low internal resistance. However, if the pH exceeds 8, the hydroquinone, which is a weak acid, starts to dissociate or oxidise into quinone, thus breaking the potential equilibrium. In addition, other substances that can bind with quinone will affect the pH measurement, such as proteins, borates, and colloidal suspensions.
(3) Antimony electrode: It is one of the metal oxide electrodes. The electrode of antimony electrode occurs between antimony metal and oxide (produced by the surface of antimony in contact with air), and since the activity of this oxide is related to the activity of OHˉ in the solution, the potential of antimony electrode is directly related to the pH value of the solution. The advantages of the antimony electrode are its simplicity of operation and its ruggedness. However, the "standard" potential of this electrode is not stable, and there are other metal oxide electrodes that can also be used for pH measurement. There are other metal oxide electrodes that can be used for pH measurement, such as the secretion (Bi) electrode, which is similar in principle and structure to the antimony electrode.
(4) Day-one mercury electrode: The saturated calomel electrode is usually used, which consists of metallic mercury, Hg2CI2 and saturated KC1 solution. It does not produce polarisation and is stable. Its electrode reaction is: Hg2CI2+2e= 2 Hg+ 2 C1ˉ.
(5) Glass Electrode: Glass pH electrode is one of the most important methods of pH measurement at present. When it is immersed in the measured solution, the hydrogen ionisation of the measured solution exchanges with the hydrated layer on the surface of the electrode bulb, and the inner layer of the bulb also generates an electrode potential. Since the hydrogen ionisation in the inner layer remains constant while the hydrogen ionisation in the outer layer changes, the potential difference between the inner and outer layers also changes, and its magnitude is determined by the concentration of hydrogen ionisation in the solution outside the membrane. This method is simple, accurate and less disturbed.
(6) Composite electrode: At present, most of them use a kind of electrode called composite electrode, i.e. glass electrode and reference electrode combined into a single probe electrode, with the combination of glass electrode and reference electrode, making the measurement more convenient, accurate and reliable.
Acidity meter (ph meter) maintenance of the instrument in addition to the correct use of the instrument more need to understand the maintenance of the instrument and the measurement of the precautions.
