Determinacion De La Constante De Equilibrio De Formación Del Triioduro
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Publicado: 8 de julio de 2012
Determination of the Equilibrium Constant for Triiodide Formation: Use of a Less Toxic Solvent
The determination of the numerical value of an equilibrium constant for a selected chemical reaction isan experiment found in most general chemistry laboratory programs. An experiment of this type which appears in several laboratory manuals1* is the determination of K., for the formation of triiodideion in aqueous solution by the reaction
An essential feature of this experiment is the equilibration of the aqueous solution with an immiscible organic phase to establish the equilibriumTitration of a portion of the organic phase with thiosulfate yields [I&,,. If Kdist is known, this permits calculation of [Iz],. From [ , and titration dataon the aqueous solution K,, can bedetermined.Published versions of this experiment employ I & carbon tetrachl~ride'.~ tetrachloroethylenes as the organic phase, probably because of the well-determined literature or values of 90.5 and 74.1respectively for K distat 2 5 T 4 We have successfully used a locally written version of the triiodide experiment employing carbon tetrachloride as the organic phase. However, the exposure of inexperiencedstudents to potentially high levels of toxic chemicals such as halogenated hydrocarbons5caused us to question the continued use of this experiment in its usual form. Others may have similar reservationsabout this otherwise attractive experiment. Rather than abandon the experiment we sought a more acceptable organic solvent and have found that reagent grade hexanes (a mixture of isomers) can besuccessfully substituted as the organic phase. I t meets the criteria of a workable Kdist value and more satisfactory exposure limits than carbon tetrachloride7 and is less expensive as well. Since thesolvent is an isomeric mixture we measured the distribution coefficient, KdiSt, and found it to be 35 i 2 a t 23°C under the conditions of the triiodide experiment. This compares with a valve of 26at...
The determination of the numerical value of an equilibrium constant for a selected chemical reaction isan experiment found in most general chemistry laboratory programs. An experiment of this type which appears in several laboratory manuals1* is the determination of K., for the formation of triiodideion in aqueous solution by the reaction
An essential feature of this experiment is the equilibration of the aqueous solution with an immiscible organic phase to establish the equilibriumTitration of a portion of the organic phase with thiosulfate yields [I&,,. If Kdist is known, this permits calculation of [Iz],. From [ , and titration dataon the aqueous solution K,, can bedetermined.Published versions of this experiment employ I & carbon tetrachl~ride'.~ tetrachloroethylenes as the organic phase, probably because of the well-determined literature or values of 90.5 and 74.1respectively for K distat 2 5 T 4 We have successfully used a locally written version of the triiodide experiment employing carbon tetrachloride as the organic phase. However, the exposure of inexperiencedstudents to potentially high levels of toxic chemicals such as halogenated hydrocarbons5caused us to question the continued use of this experiment in its usual form. Others may have similar reservationsabout this otherwise attractive experiment. Rather than abandon the experiment we sought a more acceptable organic solvent and have found that reagent grade hexanes (a mixture of isomers) can besuccessfully substituted as the organic phase. I t meets the criteria of a workable Kdist value and more satisfactory exposure limits than carbon tetrachloride7 and is less expensive as well. Since thesolvent is an isomeric mixture we measured the distribution coefficient, KdiSt, and found it to be 35 i 2 a t 23°C under the conditions of the triiodide experiment. This compares with a valve of 26at...
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