What are the characteristics of titration analysis?

Titration analysis, also known as volumetric analysis, is to drop a standard solution with a known accurate concentration into the solution to be tested (or drop the solution to be tested into the standard solution) until the added standard solution reacts quantitatively with the substance to be tested according to the stoichiometric relationship, then measure the volume consumed by the standard solution, and calculate the content of the substance to be tested according to the concentration and consumed volume of the standard solution. This quantitative analysis method is called titration analysis, which is a simple, rapid, accurate and widely used quantitative analysis method in constant analysis.

The characteristics of folding and editing this paragraph

1. The amount of substances added to the standard solution and the amount of substances to be measured are just stoichiometric;

2. This method is suitable for the determination of various substances with component content above 65438 0%;

3. The method is rapid and accurate, and the equipment and operation are simple;

4. It is widely used.

Collapse and edit this paragraph category.

According to the different reaction types of standard solutions and components to be tested, they can be divided into four categories.

1. acid-base titration-a titration analysis method based on proton transfer reaction

2. Coordination titration-a titration analysis method based on coordination reaction.

3. Redox titration-a titration analysis method based on redox reaction.

4. Precipitation titration-a titration analysis method based on precipitation reaction.

5. Medium classification of non-aqueous titration-happy titration reaction

The principle of folding and editing this paragraph

Folding titration

Titration analysis is to add a reagent solution with a known accurate concentration into the solution of the tested substance until the added reagent reacts with the tested substance quantitatively according to stoichiometry, and calculate the content of the tested substance according to the concentration of the reagent solution and the consumed volume.

This reagent solution with known exact concentration is called titration solution.

The process of adding the titration solution in the burette to the solution of the measured substance is called titration.

When the quantitative reaction between the amount of substance added in the titration solution and the amount of substance to be measured is completed according to stoichiometry, the reaction reaches the metering point.

In the process of titration, the transition point of indicator color change is called titration end point.

The titration end point does not necessarily coincide with the metering point, and the resulting analysis error is called titration error.

Folded state

The chemical reaction suitable for titration analysis shall meet the following conditions:

(1) reaction must be completed quantitatively according to the equation, which is usually required to be above 99.9%, which is the basis of quantitative calculation.

(2) The reaction can be completed quickly (sometimes heating or catalyst can be used to accelerate the reaction).

(3)*** substances do not interfere with the main reaction, or use appropriate methods to eliminate its interference.

(4) There is a relatively simple method to determine the metering point (indicating the titration end point).

Folding analysis mode

Direct titration

The so-called direct titration is the method of directly titrating the measured substance with standard solution. All chemical reactions that can meet the above three conditions at the same time can be directly titrated. Direct titration is the most commonly used and basic titration method in titration analysis. For example, NaOH is titrated with HCl and Fe2+ is titrated with K2Cr2O7.

Often some chemical reactions cannot meet the three requirements of titration analysis at the same time. At this point, you can choose one of the following methods for titration.

Back titration

Direct titration cannot be used in the following cases.

First, when the tested substance reacts slowly with the titrant in the test solution, such as Al3+ reacts with EDTA, the tested substance is hydrolyzed.

Secondly, when the solid sample is directly titrated with titrant, the reaction cannot be completed immediately. For example, HCl titration of solid CaCO3.

Thirdly, when there is no suitable indicator for some reactions or the tested substance can block the indicator, such as titration of Cl—— with AgNO3 _ 3 in acidic solution-there is no suitable indicator.

Back titration is usually used to solve these problems.

Back titration is to accurately add a certain amount of excessive standard solution to make it react with the tested substance or solid sample in the test solution, and then titrate the remaining standard solution with another standard solution after the reaction is completed.

For example, for the titration of Al ~ (3+), firstly, a known excess EDTA standard solution is added, and after the reaction between Al ~ (3+) and EDTA is completed, the remaining EDTA is back-titrated with standard Zn2+, Pb2+ or Cu2+ solution; For the titration of solid CaCO3, firstly, a known excess of HCl standard solution is added. After the reaction is completed, the remaining HCl can be titrated with standard NaOH solution. For Cl-

For titration, add a known excess of AgNO3 standard solution to make Cl-

After the precipitation is complete, the excessive Ag+ is back-titrated with the standard solution of NH4SCN with iron salt as indicator, and the end point is [Fe(SCN)]2+ reddish.

Displacement titration

For some substances that cannot be titrated directly, they can also react with another substance to replace a certain amount of titratable substances, and then titrate with a suitable titrant. This titration method is called displacement titration. For example, sodium thiosulfate cannot be used to directly titrate strong oxidants such as potassium dichromate, because the oxidant can oxidize S2O32- into S4O62- or SO42- in acidic solution, and there is no certain stoichiometric relationship. However, sodium thiosulfate is a good titrant for iodine titration. In this way, if excessive potassium iodide is added to the acidic potassium dichromate solution, a certain amount of iodine is replaced by potassium dichromate, and then iodine is directly titrated with sodium thiosulfate standard solution, the measurement relationship is very good. In practical work, this method is used to calibrate the concentration of sodium thiosulfate standard solution with potassium dichromate.

Indirect titration

Although some substances can not directly react with titrant, they can be indirectly determined by other chemical reactions.

For example, the determination of calcium by potassium permanganate method belongs to indirect titration. Because Ca2+ has no changeable valence state in solution, it cannot be directly titrated by redox method. However, if Ca2+ is precipitated into Ca2O3 _ C2O _ 4, filtered and washed, then dissolved with H2SO4 _ 4, and then C2O4 bound to Ca2+ is titrated with KMnO4 _ 4 standard solution, the content of calcium can be determined indirectly.

Obviously, due to the application of back titration, displacement titration and indirect titration, the application scope of titration analysis has been greatly expanded.