Introduction

Bromine is a commonly used reagent in chemistry, because of its volatile and unstable characteristics, so the determination of its content has become the center of research. In traditional chemical analysis, the determination of bromine content is usually determined by REDOX titration, coordination titration, precipitation titration and other methods.At present, most of the bromine content is determined by precipitation titration in analytical laboratories. After years of practice, it is found that these methods have a series of problems such as incomplete reaction, many interfering ions, cumbersome analysis process and low accuracy of analysis results, which bring a lot of inconvenience to experimental teaching and students' operation. In recent years, after gradually exploring, finally found a method that can replace the traditional analysis method to determine the content of bromine, which is spectrophotometry. This method is based on H2SO4 as the medium, under a certain acidity condition, the soluble bromide is oxidized with KMmO4, and the absorbance is measured after extraction with CCl4. The analytical results are consistent with the traditional analytical method, and it is accurate, rapid and simple.

Experimental purpose

The content of bromine was determined by spectrophotometry and precipitation titration respectively, and the results were compared to prove that the content of bromine was determined by spectrophotometry.

xperimental instruments and reagents

Macylab UV1300 UV-Vis Spectrophotometer、PH acidimeter、3.0mol/l H2SO4 solution, 0.10mol/l KMnO4 solution, 0.0100mol/l KBr standard solution, 0.1000mol/l Br standard solution, organic solvent CCl4, and glass instruments commonly used in analytical experiments.

Working curve

Under the condition of maximum absorption wavelength of 482nm and molar absorption coefficient of 1.01×1-3L/cm 'mol, Br2- was prepared with 0.1000 mol/L Br2 standard solution by step dilution method In CCl4 solution, the luminosity of Br with different concentration was measured, and the working curve of CBr2-A was made on the coordinate paper with the concentration of Br as the horizontal coordinate and the absorbance as the vertical coordinate. The two-function curve was in accordance with Lambert-Behr law, which was used for calculating the content of bromine.

Acidity condition

After many experiments, it has been shown that the chemical reaction based on this method is the most complete and the fastest reaction between PH 0 and 0.3, so the acidity of the experiment is required to be controlled at PH 0 l or so.

Oxidant selection

Through the experiments of various oxidants, among them, the reaction phenomenon of KMnO4 and bromide is the most obvious, and the color change is the most easy to distinguish, so KMnO4 is selected as an oxidant.

The effect of interfering ions

After the sample is treated by the conditions of the above experimental steps, the common Ca2+, Mg2+, CI-, Ba2+ plasma which is not easy to remove does not interfere with the determination.

Analysis result

After the above experimental steps, for the determination of the same sample, the analytical results of spectrophotometry and precipitation titration are consistent. Through the determination of KBr standard solution of different concentrations, MgBr2, CaBr2 and other samples, the maximum deviation between this method and precipitation titration is about 0 04‰.

Precision test

The relative standard deviation of a sample is 1.5, and the reproducibility is good.