Heng Aode's practical application method for analyzing redox potential
The redox potential is used to reflect the macroscopic oxidation-reduction properties exhibited by all substances in an aqueous solution. The higher the oxidation-reduction potential, the stronger the oxidizability, and the lower the potential, the weaker the oxidizing property. A positive potential indicates that the solution exhibits a certain degree of oxidative properties, and a negative indicates that the solution exhibits reducibility.
Basic explanation
Oxidation-reduction potential, redox potential Regardless of the reaction form, the so-called oxidation is the loss of electrons. The so-called reduction is the electron, which must be accompanied by the electron transfer process. When a platinum electrode is inserted into the reversible redox system AH2 A 2e 2H, electrons are supplied to the electrode and become a half-cell having a potential corresponding to the reducing power of the system. The potential measured by combining it with a standard hydrogen electrode is the redox potential of the system. The redox potential value Eh is determined by the free energy (or equilibrium constant) of the oxidized H2 reduced form, the pH, the ratio of the oxidized form to the reduced form [ox]/[red], and the following formula is obtained:
(R is the gas constant, T is the absolute temperature, F is the Faraday constant, and n is the number of electrons associated with the redox of the system). E' is Eh when the oxidized form and the reduced form are equal. The standard potential at a pH of F is an index indicating the redox ability peculiar to the system. When the Eh corresponding reduction rate is plotted, E0 is a symmetrical S-shaped curve. Eh high is able to oxidize Eh low, and when Eh is equal, it reaches equilibrium. However, this is only a phenomenon that occurs in thermodynamics.
The so-called redox potential is used to reflect the macroscopic oxidation-reduction properties exhibited by all substances in an aqueous solution. The higher the oxidation-reduction potential, the stronger the oxidizability, and the lower the potential, the weaker the oxidizing property. A positive potential indicates that the solution exhibits a certain degree of oxidative properties, and a negative indicates that the solution exhibits reducibility.
Practical application
In fact, especially for most biological systems, no recognizable reactions occur without enzymes and electron mediators. The redox potential can be determined directly from the potential, and can be obtained by using a redox indicator according to the calculation of the equilibrium constant. In general, electron transport in the living body is directed from a direction in which the oxidation-reduction potential is low, for example, a tendency to proceed in a manner such as NAD→flavinase→cytochrome C system→O2, but also due to the specificity of the enzyme and The inhibition is not carried out in this manner, and it is also possible that a system having a low standard potential oxidizes a high system due to the concentration of the reaction component. In the redox system of organisms, polyphenols and cytochromes C, a, etc. are in the vicinity of 200-300 mV, cytochrome b and flavinase are in the range of 0--100 mV, and in the -330 mV position, NAD is in -420 mV. The location is iron redox protein. In living cells, aerobic cell potential is high, anaerobic potential is low, enzyme activity and cell assimilation ability, and growth and development of microorganisms are also affected by oxidation-reduction potential.
Potential measurement
Measuring meaning
For a water body, there are often multiple redox couples that form a complex redox system. The oxidation-reduction potential is a combined result of redox reactions between various oxidizing substances and reducing substances. Although this index can not be used as an indicator of the concentration of certain oxidizing substances and reducing substances, it is helpful to understand the electrochemical characteristics of water bodies and analyze the properties of water bodies.
test methods
A platinum electrode is used as an indicator electrode, a saturated calomel electrode is used as a reference electrode, and a primary battery is formed with a water sample. The oxidation-reduction potential of the platinum electrode relative to the saturated calomel electrode was measured using an electronic millivoltmeter or a universal pH meter, and then the oxidation-reduction potential of the composition relative to the standard hydrogen electrode was converted as a report result.
Calculation formula: Ψn = Ψind + Ψref
Where: Ψn -- the redox potential of the water sample being tested, mV;
Ψind -- the measured redox potential of the water sample, mV;
Ψref -- The electrode potential of the saturated calomel electrode at measured temperature, mV, can be found in the Handbook of Physical Chemistry.
Precautions
The redox potential of the water must be measured in the field.
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The redox potential is affected by factors such as solution temperature, pH, and reversibility of chemical reactions.
ORP determination
Do I need to correct the ORP standard solution when measuring ORP?
The ORP meter can be used without calibration. Only when there is any doubt about the quality or test results of the ORP electrode, the electrode potential can be checked with the ORP standard solution to determine whether the ORP electrode or instrument is good or bad. When required, the new platinum electrode should be checked for electrode potential using the ORP standard solution.
Measuring electrode
1. The redox electrode can be used on any pH/mv meter.
2. When the ORP meter is used, it can be used without calibration. If there is any doubt about the quality or test result of the ORP electrode, the ORP standard solution can be used to check whether the potential is between 200-275mv to judge whether the ORP electrode or the instrument is good or bad. . Redox electrode instruction manual redox electrode instruction manual redox electrode instruction manual
3. ORP measuring electrode (platinum or gold), the surface should be bright, rough or contaminated surface will affect the potential (mv) of the electrode. The activation can be washed by the following method.
(1) For inorganic contamination, the electrode can be immersed in 0.1 mol/L dilute hydrochloric acid for 30 minutes, washed with pure water, and immersed in 3.5 MOL/L potassium chloride solution for 6 hours before use.
(2) For the contamination of organic oil and oil film, the surface of platinum or gold can be washed with detergent and then washed with pure water, and then immersed in 3.5MOL/L potassium chloride solution for 6 hours.
(3) Platinum surface contamination seriously forms an oxide film. The surface of platinum or gold can be polished with toothpaste, then washed with pure water, and then immersed in 3.5MOL/L potassium chloride solution for 6 hours.
Measuring meaning
The filtration system, which removes denitrification, is actually an oxidative biochemical filtration device. For organic matter, microorganisms oxidize to break longer carbon chains (or open various carbon rings), and then undergo complex biochemical processes to finally oxidize various forms of organic carbon to carbon dioxide; at the same time, these oxidations Substances such as nitrogen, phosphorus, sulfur, etc. are cleaved from the corresponding carbon bonds to form corresponding inorganic substances. For inorganic substances, microorganisms oxidize low-valent inorganic substances to high-valent substances by oxidation. This is the essence of oxidative biochemical filtration (here we only care about those substances that are oxidatively decomposed by microorganisms, and not those that are absorbed and assimilated by microorganisms). It can be seen that while biochemical filtration, the substance in the water is continuously oxidized. The process of biochemical oxidation is accompanied by the continuous formation of oxidation products, so the redox potential is continuously improved from a macroscopic point of view. Therefore, from this point of view, the higher the oxidation-reduction potential, the more thoroughly the pollutants in the water are filtered.
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