k2cr4 - HNO3 - KNO3 - H2O和K2Cr2O7 - NaOH - KNO3 - H2O体系水溶液中的平衡过程

Y. Oleksii, O. Mariichak, G. M. Rozantsev, S. A. Shyshkanov, S. V. Radio
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摘要

采用pH电位滴定法、数学模型和UV-Vis研究了cr2o42 - - H+ - H2O和Cr2O72 - - OH - - H2O体系在水溶液中的平衡过程。光谱学。建立了在酸度ZН = ν(H+)/ν(Cr(VI)) = 0-2.5的CrO42 - - H+ - H2O体系中,发生重铬酸盐和氢铬酸盐阴离子形成和重铬酸盐水解转化为氢铬酸盐的过程,并利用准牛顿法(CLINP 2.1软件;95%置信概率)。浓度平衡常数lgKC的对数计算值与文献数据吻合较好。利用计算得到的lgKC建立了溶液中铬(VI)阴离子随ZH和ZOH的分布图。首次采用Pitzer方法计算了由cro2 -和H+离子生成氢铬酸盐HCrO4 - (lgK10 = 6,94)、重铬酸盐阴离子Cr2O72 - (lgK20 = 15,49)的热力学平衡常数,以及重铬酸盐阴离子与氢铬酸盐阴离子(lgK30 = - 1,61)相互转化平衡常数的对数。数学建模与UV-Vis。光谱分析表明,在碱度ZOH = ν(OH -)/ν(Cr(VI)) = 0-2.5的Cr2O72 - - OH - - H2O溶液中,阴离子的组成与CrO42 - - H+ - H2O体系相同。在相同离子强度的CrO42 - - H+ - H2O溶液中,通过重铬酸盐阴离子水解成氢铬酸盐阴离子,再中和成铬酸盐阴离子,可以可靠地再现Cr2O72 - - OH - - H2O体系的实验依赖关系pH = f(Z),并计算出各过程的平衡常数。用紫外-可见光谱法定性确定了六价铬溶液的定量组成。光谱学。
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EQUILIBRIA PROCESSES IN AQUEOUS SOLUTIONS OF K2CrO4 – HNO3 – KNO3 – H2O AND K2Cr2O7 – NaOH – KNO3 – H2O SYSTEMS
The equilibria processes in aqueous solutions of CrO42– – H+ – H2O and Cr2O72– – OH– – H2O systems were studied by pH‑potentiometric titration, mathematical modeling and UV–Vis. spectroscopy. It was established that in the CrO42– – H+ – H2O systems with acidity ZН = ν(H+)/ν(Cr(VI)) = 0–2.5 the processes of dichromate and hydrochromate anion formation and hydrolytic conversion of dichromate to hydrochromate take place, for which the logarithms of the equilibrium concentration constants were calculated by the quasi-Newton method (CLINP 2.1 software; 95 % confidence probability). The calculated values of the logarithms of the concentration equilibrium constants lgKC reliably agree with the literature data. The calculated lgKC were used to build of chromium(VI) anions distribution diagrams depending on ZH, and ZOH in solutions. For the first time, by the Pitzer method the thermodynamic equilibria constants of hydrochromate HCrO4– (lgK10 = 6,94), the dichromate anion Cr2O72– (lgK20 = 15,49) formation processes from the CrO4 2– and H+ ions, and the logarithm of equilibrium constant of the interconversion of the dichromate anion to the hydrochromate anion (lgK30 = –1,61) were calculated. Mathematical modeling and UV–Vis. spectroscopy show that the composition of anions in Cr2O72– – OH– – H2O solutions with alkality ZOH = ν(OH–)/ν(Cr(VI)) = 0–2.5 is identical to CrO42– – H+ – H2O systems. It is established that the experimental dependencies pH = f(Z) for the Cr2O72– – OH– – H2O system can be reliably reproduced by hydrolysis reactions of dichromate anion to hydrochromate anion and by subsequent neutralization to chromate anion with equilibrium constants calculated for processes in CrO42– – H+ – H2O solutions with same ionic strengths. The quantitative composition of chromium(VI) solutions was confirmed qualitatively by UV–Vis. spectroscopy.
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