ammonium-citrate buffers, cation-molecular complexes, ionic associates, electrical conductivity, density


Acid-base and electrochemical behavior in the systems H3Cit – Am – H2O (H3Cit – citric acid; Am – monoethanolamine and polyethylene polyamine) and their structural characteristics features establishment is an urgent task. The pH and conductometric study of protolytic equilibria in the systems HOC3H4(COOH)3 – NH2CH2CH2OH – H2O and HOC3H4(COOH)3 – NH2(CH2CH2NH)kH – H2O was carried out with the total content of citrate forms (citric acid, dihydrogen citrate, hydrogen citrate and citrate anions, cation-molecular complexes and ionic associates) 1.0 M in the temperature range 293 – 313 K. Intermolecular interactions in these systems were estimated in comparison with sodium citrate – citric acid – water solutions at 298 K. The order of components adding affects resulting solutions pH values in contrast to the specific electrical conductivity and density. With the same total citrates content according to the specific electrical conductivity values the studied systems can be arranged in such series: HOC3H4(COONa)3 – HOC3H4(COOH)3 – H2O > NH2CH2CH2OH – HOC3H4(COOH)3 – H2O > NH2(CH2CH2NH)kH – HOC3H4(COOH)3 – H2O. This is because of the mobility of cations and the additional formation of cation-molecular complexes and ionic associates due to H-bonding in the monoethanolamine and polyethylene polyamine systems. According to densitometry, the organic amine (monoethanolamine or polyethylene polyamine) introduction into an citric acid aqueous solution in contrast to sodium citrate results the structuring of the system. The breaks positions on the densitometric curves correspond to the breaks on the conductometric curves; the studied solutions specific electrical conductivity values correlate with their density. The investigated solutions cation-molecular compositions and ionic strengths were calculated. The cation-molecular complexes and ionic associates concentration and thermodynamic formation constants estimation was carried out. The obtained results can be useful to evaluate of the solutions studied in this work buffer properties as well as for developing of chemisorbents based on them.


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Physical and inorganic chemistry