Reaction endpoint judgment device and five-step iodometry

Abstract

The invention discloses a reaction endpoint judgment device. The device comprises a reaction container, a burette arranged above the reaction container, a monochromatic light source arranged on one side of the outside of the reaction container and a photoelectric receiver located on the other side of the reaction container and opposite to the monochromatic light source, wherein the photoelectric receiver is connected with a data processing system. The invention further discloses five-step iodometry without the step of starch adding. The device and the method effectively solve the problems that color change of a reaction endpoint is influenced and errors are caused to judgment of the titration endpoint due to the fact that a starch indictor is likely to have a reaction with high-concentration iodine in advance in step 2 and step 4 in traditional five-step iodometry and starch forms colloid and wraps the iodine, the device is simple in structure, the method is simple and convenient to operate, and the sensitivity and the accuracy are high.

Description

technical field [0001] The invention belongs to the technical field of disinfectant detection, and in particular relates to a reaction terminal judging device and a five-step iodometric method without adding starch. Background technique [0002] Appendix A of the national standard GB28931-2012 provides a method for detecting the content of chlorine dioxide, chlorine gas, chlorite ions, and chlorate ions produced by chlorine dioxide disinfectant generators, called the five-step iodometric method. The detection principle is to use ClO under different pH conditions 2 , Cl 2 , ClO 2 - , ClO 3 - respectively with I - The reaction produces elemental iodine, and the resulting iodine is titrated with sodium thiosulfate. The detection process is divided into five steps, so it is called the five-step iodometric method. The amount of sodium thiosulfate consumed in each step is used to calculate the amount of each substance. content. [0003] Each step of the traditional five-st...

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Problems solved by technology

[0004] The second step of the five-step iodometric method is to continue adding hydrochloric acid to the solution on the basis of the first step to make the pH ≤ 2. At this time, the chlorite converted from the reaction of chlorine dioxide in the first step and the chlorous acid contained in the sample itself Salt participates in the reaction to produce a large amount of iodine. The solution in the second step already contains starch indicator. At this time, because the solution contains a large amount of iodine, the starch will form a colloid to cover the iodine, which will affect the color change of the titration end point and affect the titration end point. error in judgment

[0005] The problem to be solved in the present invention is that in the five-step iodometric method, the starch indicator of the second and fourth steps is ahead of schedule with high-concentration iodine simple substance (I 2 ) reaction, the starch will form a colloid to wrap the iodine element, which will affect the color change of the titration end point, and the judgment of the titration end point will cause errors

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