The complexes of ethylendiamine-tetraacetic acid with heavy metalsReport as inadecuate


The complexes of ethylendiamine-tetraacetic acid with heavy metals


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Abstract

The research presented here was concerned with thedetermination of the number and composition of the complexesof the heavy metals, nickel, cobalt, copper, ferric ironand aluminum, with ethylenediamine-tetraacetic acid. Potentiometric titrations of ethylenediamine-tetraaceticacid plus a heavy metal with sodium hydroxide showeda lowering of pH when compared with the titration of theacid alone. This proved that complexes were being formedand that during this formation protons were given off, thuslowering the pH. Different curves, each with definite levelareas where reactions were taking place, were obtained whendifferent ratios of metal to acid were used. Thus complexeswere formed containing different numbers of acidmolecules and metal atoms. When an ion of ethylenediamine-tetraacetic acid wastitrated potentiometrically against a metal ion, pH jumpsand leveling of the pH occurred at definite ratios of metalto acid. In these cases one complex formed, which, uponaddition of more metal ion, formed another complex differingin both metal to acid ratio and in hydrogen ion or hydroxylion content. Vihen the second reaction was complet,ed the pHleveled off. Thus these pH curves, in which pH was plottedagainst the molar metal to acid ratio, determined the compositionof each complex as far as the number of metal atomsand acid molecules were concerned. The curves also indicated that hydrogen or hydroxyl groups were contained in the complexes. Conductimetric titrations of each acid ion against eachmetal ion were carried out. A break in the linear curve ofthe conductivity plotted against the molar ratio of metalion concentration to acid ion concentration showed the numberof metal atoms and acid molecules present in each complex.These results corroborated those of the previouslymentioned potentiometric titrations. Solutions of acid ion and metal ion were then mixed sothat the molar metal to acid ratio was that of the complexbetween the two ions, thus the ratio found above. The resultingsolutions were then titrated with base or acid.If in the case of titration with base a normal acid basecurve was obtained when pH was plotted against the molarratio of added hydroxyl ion to the total ethylenediaminetetraaceticacid in the solution, then the protons reactingwith the base were freed when the complex was formed. Ifthe curve was not a normal one, the hydroxyl ion reactedwith the complex directly. When hydrochloric acid was usedinstead of base in the titration, if a pH jump occurred,protons were being taken up by the complex. In each casethe pH jumps occurred at definite molar ratios of hydroxylion to total ethylenediaruine-tetraacetic acid or of hydrogenion to total tetraacetic acid, thus showing how manyhydrogens were given off in the formation of the complex,hydrogens were given off in the formation of the complex,and how many hydroxyl or hydrogen ions were taken up by anycomplex to form a new complex. Equations were then written, which agreed with the combinedresults obtained above. From these equations thecomposition of each complex was known.Rights

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Dissertations and Theses pre-1964 -



Author: Baker, Ann Eldora - -

Source: https://open.bu.edu/



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