How does redox titration work? It s best to give an example thanks

Experimental video: Redox titration.

The electrode potential changes during the titration1.The reaction equilibrium constant must be greater than 106, i.e., e>.

2.The response is rapid, and there is no side reaction, the reaction should be complete, and there is a certain measurement relationship.

3.The substances participating in the reaction must be oxidizing and reducing or can form precipitates with reducing agents or oxidants.

4.Appropriate indicators should be available to determine the endpoint. Redox balance titration is a titration analysis method based on the transfer of electrons between oxidants and reducing agents in solution.

Compared with acid-base mask imitation titration and coordination titration, redox titration is widely used, which can not only be used for inorganic boredom analysis, but also can be widely used for organic analysis

The electrode potential changes during the titration

According to my body of knowledge, the commonly used redox titration methods include iodine method, potassium permanganate method, potassium dichromate method, potassium bromate method, cerium method, etc. In the case of iodometry, the titration principle is a redox titration method that uses iodine as an oxidant or iodine ions as a reducing agent. The main principle is that the solubility of iodine in water is very small, and when the iodine solution is configured, the solid iodine is often dissolved in the potassium iodide solution, and the iodine element is combined with iodine ions to form iodine triions, thereby increasing the solubility.

From the above, it can be seen that iodine is a weak oxidant, which can only oxidize substances with strong reducing properties, while iodine ions are a medium-strength reducing agent, which can reduce many oxidizing substances, therefore, the iodine measurement method can be carried out in two ways: direct titration or indirect titration. The iodometric method can determine both oxidants and reducing agents. The iodine triion and iodine ion electric pairs reflect good reversibility, few side reactions, and a very sensitive starch indicator to indicate the end point, so the iodine dosimetry has a wide range of applications.

Direct iodine titration, also known as iodine titration, is a titration analysis method for direct titration of reducing substances by iodine elemental standard solution. However, the direct iodine dosing method can not be carried out in the alkaline solution, when the pH of the solution is greater than 8, the partial iodine element will undergo disproportionation reaction, this reaction will bring errors, and only the reduction ability is strong in the acidic solution, and the substances that are not affected by the concentration of hydrogen ions can have a quantitative reaction, and because the standard electrode potential of iodine is not high, the direct iodine dosing method is not as widely used as the indirect iodine dosing method. Indirect iodine measurement method, also known as titration method, oxidizing substances with higher electrode potential than iodine pairs, can be quantitatively replaced with iodine ion reduction under certain conditions, and then replaced with iodine element by titration with Na2S2O3 standard solution, which is indirect iodine measurement method.

Many oxidizing substances can be determined. Potassium permanganate is a redox titration method with potassium permanganate as the standard solution, potassium permanganate is a strong oxidant, its oxidation ability and reduction products are related to the acidity of the solution, the root of permanganate itself is unstable, can be disproportionated to form manganese dioxide and manganate. The potassium permanganate method is usually a reaction that uses the permanganate group in a strong acidic solution to be reduced to divalent manganese ions, because hydrochloric acid has reductive properties, potassium permanganate can be oxidized, and it is not suitable to use, and nitric acid is oxidizing and does not need to adjust the acidity of the solution, and sulfuric acid is commonly used, and the acidity should be controlled at one to two moles per liter.

According to the nature of the measured substance, direct titration, back titration, indirect titration, etc. can also be used. The potassium dichromate method is the property of using potassium dichromate, a strong oxidant, to reduce itself to trivalent chromium ions when it reacts with reducing substances in an acidic medium. Because potassium dichromate itself is orange, but its reduction product trivalent chromium ion is green, which has a serious impact on the observation of orange, it cannot be used to indicate the end point of its own use, and sodium diphenylamine sulfate is often used as an indicator.

If there are two remaining potassium bromate methods, bromine and cerium methods, if you want to know, you can continue to ask.

Redox titration is widely used in chemical analysis, which can be used to determine the equivalence relationship of redox reactions in various substances, and has become an indispensable method in chemical analysis.

1.Basic principles of redox titration

Redox titration is a simple and effective quantitative analysis method, the basic principle of which is to use the equivalence relationship of redox reaction to determine the content of a substance, which is manifested in the reaction between the standard solution and the solution to be measured to determine the charge state of an element.

2.The specific operation process of redox titration.

a.Select a suitable indicator according to the characteristics of the solution to be tested.

b.Prepare the standard solution and calculate the appropriate dosage range for the experiment based on experience or theory.

c.Fill the test solution into a graduated cylinder and add a sufficient amount of the appropriate indicator to give it a specific color.

d.Under agitation, a normalized solution is added to the sample to be tested, and if needed, an acidizing or alkalizing agent is added to adjust the pH of the solution.

e.Observe the change in the color of the indicator, and determine the volume of the standard solution to be added dropwise based on the change in color.

f.According to the volume of the normalized solution and the measured sample, the content of a certain substance in the measured sample is calculated.

3.Areas of application for redox titration

Redox titration has such an important position and significance in the field of chemical analysis, and it is mainly used in the quantitative analysis of various samples containing reducing substances, such as production industry, medicine and health, environmental protection and other fields. For example, redox titration can be used to determine oxidizing substances in water and food, elemental sulfur and peroxides in pharmaceuticals.

4.Concentration calculations and error analysis

Concentration calculations for redox titration are challenging, and a variety of factors need to be taken into account in order to obtain accurate results, such as the effects of the standard solution prepared with caution and the effects of multiple components in the analyte sample. In addition, human factors such as experimental operation errors may also affect the experimental results, and the quantification error is large.

5.Summary

In conclusion, redox titration is a well-established analytical method with a wide range of local applications in chemistry and other applications, which can provide experimental data support for researchers in various industries. However, this experiment requires precision to obtain true and accurate data results.

The commonly used redox titration methods are as follows: iodine titration, potassium permanganate titration, and potassium dichromate titration.

Extended information: Iodometric methods are widely used because the oxidation and reduction potentials of iodine are very close, so they can be titrated and titrated directly; The reaction of potassium permanganate under acidic, neutral and alkaline conditions is different, and it is generally titrated under acidic conditions.

Potassium dichromate titration is also partially used. Redox titration is a titration analysis method based on the electron transfer between the oxidant and the reducing agent in solution.

Compared with acid-base titration and coordination titration, redox titration is widely used, it can not only be used for inorganic analysis, but also can be widely used in organic analysis, many oxidizing or reducing organic compounds can be determined by redox titration.

The basic reflection: the equivalence point of redox titration can be determined with the help of instruments (such as potentiometric analysis), and some titrant solutions or titrated substances themselves have a deep enough color, if they fade after the reaction, they can themselves act as indicators, such as potassium permanganate.

Soluble starch and trace amounts of iodine can produce a dark blue color, and when iodine is reduced to iodine ions, the dark blue color disappears, so in iodine dometry, starch solution is usually used as an indicator.

Indicators of redox reactions, such as sodium diphenylamine sulfonate, methylene blue, etc., also undergo redox reactions when the titration reaches the equivalence point, and the color of the oxidation state and the reduced state is significantly different, thus indicating the end point of the titration.

For example, sodium diphenylamine sulfonate exists in the form of aniline sulfonic acid in an acidic solution, colorless, and when oxidized by the standard titration solution, diphenyl biphenyl sulfonic acid is generated, purple.

It can produce special color with oxidant reducing agent, which significantly improves the sensitivity of observation, such as in iodine titration, soluble starch solution and iodine standard titration solution form dark blue adsorbent compounds, which are reversible. For example, when the potassium permanganate standard titration solution titrates the product oxalic acid, the titration endpoint is the purple color of the potassium permanganate standard titration solution.

During the titration process, the electrode is stuffy and the potential changes1.Reaction equilibrium constant.

Must be greater than 106, i.e. e>.

2.The reaction is rapid, and there is no side reaction, the reaction should be complete, and there is a certain balance measurement relationship.

3.The substances participating in the reaction must be oxidizing.

and reducing or can be with reducing agents.

or the substance in which the oxidant generates a precipitate.

4.Appropriate indicators should be available to determine the endpoint. Redox titration is a titration analysis method based on the transfer of electrons between oxidants and reducing agents in solution.

Compared with acid-base titration and coordination titration, redox titration is very widely used, which can be used not only for coverless imitation machine analysis, but also widely used for organic analysis