QUANTITATIVE DETERMINATION OF COPPER CONCENTRATION IN AQUEOUS SOLUTION BY IODOMETRIC TITRATION

Topics: Iodine, Reducing agent, Redox Pages: 5 (1690 words) Published: April 21, 2014
EXPERIMENT 8
QUANTITATIVE DETERMINATION
IODOMETRIC TITRATION

OF COPPER CONCENTRATION IN

AQUEOUS SOLUTION B Y

RESULTS AND DISCUSSION
Considered as moderately weak oxidizing agent, Iodine was used for the determination of strong reductants. Standard iodine solutions were found to have smaller electrode potentials as compared with the other oxidants, gaining them the advantage of imparting a degree of selectivity essential in the determination of strong reducing agents amid the presence of weak agents. Although regular re-standardization was essential for Iodine solution due to its lack of stability, it was still suitable for titrations due to its advantage of having sensitive and reversible indicator [5]. Reduction-oxidation titrations involving iodine were classified mainly into two; Iodimetry and Iodometry. Iodimetry was a direct method involving only one reaction between the titrant and the analyte [6].

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In Reaction 1, the analyte of unknown concentration was titrated against the standard Iodine solution. It reduced the titrant, Iodine (I2), into Iodide; while the titrant acted as oxidizing agent to the analyte. The reduction of iodine was dependent on the strength of its reducing agents; weakest reducing agents do not proceed to completion due to Iodine’s comparatively weak oxidizing capacity; stronger reducing agents were favored only under neutral conditions. However, even in acidic solutions, strong reducing agents could proceed into completion without difficulty. Reducing agents: sulfide, sulfite, thiosulfate, arsenite, ferrocyanide, stannous, and antimonous ions were determined to be strong reducing agents, enough to reduce Iodine; this limit therefore, implicates the few titrations which involve Iodimetry [6].

Iodometry, on the other hand was an indirect method which allowed the reaction of oxidizing agents with neutral or acidic solution of a soluble Iodide. In this method, Iodine was liberated in equivalent amount prior to the titration with standard reducing agent. Sodium thiosulfate was often used which was oxidized to sodium tetrathionate [6]. The reactions involved were: (

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1

Presented in Reactions 2 & 3 were the reactions involved in the indirect process. The principal reaction involved was the reduction of iodine to iodide by thiosulfate. The process was similar to Iodimetry except for the excess I - used. The strong reducing agent, hydriodic acid, allowed this method to determine larger number of oxidizing agents. The widely determined ions include iodine, chlorine, bromine, iodate, periodate, hypobromite, bromate, hypochlorite, chlorite, chlorate, persulfate, hydrogen peroxide, nitrite, arsenate, ferrycyanide, chromate, permanganate, manganese dioxide and higher oxides, ferric, cupric, and antimonic ions [4][6]. With this, Iodometry, was therefore applied in more titrations than Iodimetry.

Iodometry was used in the analysis of the shelf life of pharmaceuticals. This method was used in this study to quantitatively determine the concentration of copper in aqueous solution. The Iodide ions reacted with the Cu(II) to form insoluble Copper(I) iodide and iodine in Reaction 4.

Since solid Iodine was not soluble in water, the solid was dissolved into potassium iodide providing the excess amount of I-. Iodine reacted with iodine produced triiodide ion manifested in Reaction 5 [6]

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Upon titration with Na 2S2O3·5H2O, the reaction proceeds as illustrated in Reaction 6.

The end point was made sharper by the addition of KSCN in Reaction 7.

The primary standard used in the study was CuSO 4·5H2O; and the titrant used was Na2S2O3·5H2O.Sodium thiosulfate was not used as the primary standard since it can be completely oxidized to sulfate, which was not suitable for volumetric processes [6]. The preparation of the solution should not be based exactly through its weight because of its efflorescent salt and...
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