Analysis of some electrochemical processes related to coulometric titrations at constant current
✍ Scribed by Paul Delahay
- Publisher
- Elsevier Science
- Year
- 1952
- Tongue
- English
- Weight
- 872 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0003-2670
No coin nor oath required. For personal study only.
✦ Synopsis
In coulometric titrations at constant current, the reagent is generated by a suitable electrolytic process which generally takes place in the vessel containing the solution being titrated. The amount of reagent consumed in a titration is proportional to the quantity of electricity used in the generation of the reagent; and consequently the concentration of the analyzed substance can be calculated by application of Faraday's law. In order to simplify the measurements, the generator current is generally kept constant throughout the titration. Under these conditions the quantity of electricity consumed in a titration is equal to the product of the generator current by the time of generation. These two quantities can easily be measured with accuracy. Titrations with the following generated reagents have been reported thus far: chlorind, bromineaB7, iodine*, hydroxyl ionsdl, cuprous ion x2, ferrous iox?. Titrations with externally generated reagent flowing into the reaction vessel were recently described'*.
The amount of reagent consumed in a titration can be calculated on the basis of Faraday's law only when the efficiency of the generation process is IOO per cent. The conditions under which this efficiency is obtained should be determined cxpcrimentally, but it is profitable to make a careful analysis of the electrochemical processes involved in a titration before undertaking any experimental work. This point is illustrated in the present paper by a few specific examples. Various factors which determine the efficiency of a generation process will be studied first ; and finally two titrations, already described in the literature, will be analyzed.
EFFICIENCY OF GENERATION PROCESS
If the reagent is to be generated quantitatively, the following processes should not occur at the generator electrode : I. The evolution of hydrogen when the generation is a cathodic process ; 2. The evolution of oxygen when the generation is an anodic process; 3. The oxidation of the anode material when the generation is an anodic process.