A Variety of Electrochemical Methods in a Coulometric Titration Experiment

Abstract

An experiment for a practical course is described in which the amounts of HCl and KI in a mixture of standardized solutions are determined by three coulometric titrations. The iodide content is titrated with bromine that is generated at the anode from bromide which oxidizes the I- to I2 and further to IBr2-. The titration is followed with a twin-polarizable platinum electrode which essentially records the I2 and (after the endpoint) Br2 levels. Analysis of the chloride content is performed indirectly by titration of the acid through cathodic reduction of H+ to H2. The titration is monitored with a glass electrode. Finally I- and Cl- are determined simultaneously by anodic dissolution of a silver wire with a silver electrode recording the course of the titration. The experiment provides an internal check of the quality of the analysis and presents a variety of electrochemical methods of pedagogical value. Hints for the practical performance of the experiment in laboratory courses are given, and the necessary electronic circuits for self-assembling are described. Laboratory experiences with students' data collection by hand, recorder and computer are dealt with in this experiment. A complete list of earlier papers is provided, which can be found in this Journal, on the subject of coulometric analysis.

Coulometric Titrations in Wine Samples: Studies on the Determination of S(IV) and the Formation of Adducts

“…Good possibilities would involve endpoint detection by instrumental methods; amperometry and biamperometry are well suited. Discussions of the difference between electrodes used to generate the titrant (and side products at the cathode) and those used to monitor the electroactive species (I 3 ᎑ ) or the reversible couple (I 3 ᎑ /I ᎑ ) are always useful to teach relevant aspects of electroanalytical chemistry (15). The possibility of titrating organic acids in wine samples by using the cathode as a source for producing OH ᎑ ions quantitatively would also be discussed.…”

Coulometric Analysis Experiment for the Undergraduate Chemistry Laboratory

“…The coulometric methods of chemical analysis are well-known, and undergraduate experiments based on coulometric methods are common in the quantitative analysis course. Numerous reports on coulometric methods with the pedagogical objectives have appeared in this Journal . − A variety of forms of a coulometry cell made of glass have been reported, and special care is required to clean and assemble the parts of a cell made of glass. The volume of the electrolyte used in these cells is in the range of tens of milliliters or higher. − The coulometry autotitrator cells are expensive .…”

“…Numerous reports on coulometric methods with the pedagogical objectives have appeared in this Journal . − A variety of forms of a coulometry cell made of glass have been reported, and special care is required to clean and assemble the parts of a cell made of glass. The volume of the electrolyte used in these cells is in the range of tens of milliliters or higher. − The coulometry autotitrator cells are expensive . A “salt bridge” is often used ,,,,− to physically separate the anode and cathode compartment contents and to allow the current to flow through the cell.…”

“…The volume of the electrolyte used in these cells is in the range of tens of milliliters or higher. − The coulometry autotitrator cells are expensive . A “salt bridge” is often used ,,,,− to physically separate the anode and cathode compartment contents and to allow the current to flow through the cell. A salt bridge used in a coulometer setup is made of fragile sintered glass or a U-shaped tube filled with an agar–electrolyte mixture.…”

Simple and Automated Coulometric Titration of Acid Using Nonisolated Electrodes

“…Coulomeric titrations are an important part of both the analytical chemistry and instrumental analysis curricula. As a result, a large number of coulometric titrations have been reported in this Journal , − including determinations of cyclohexene, acid, iodide, and sulfites in wine . Coulometric titrations simplify the titration process because they eliminate the need for the preparation of primary standard solutions , and allow for facile generation of unstable reagents such as Br 2 . , Unfortunately, the coulometric titrations previously reported include − the use of expensive coulometers, complicated experimental apparatus, and complex circuitry.…”