Abstract
Potassium iodide was titrated in 2-15% sulfuric acid solution with 0.02N or 0.001N potassium permanganate and this titration was followed by absorption at 290mμ, the absorption maximum of the periodide ion, and photometric titration curve shown in Fig. 2 was obtained. This curve was understood to mean that, when periodide ion, with absorption maximum at 290mμ, is formed when I2 separates out from I-, the absorbance increases until equilibrium is reached, the absorbance decreases thereafter as I2 forms in excess, and the minimum absorbance is shown when all I- turns into I2. At this point, 1cc. of 0.001M KI was calculated to correspond to 1cc. of 0.001N KMnO4 and the value agreed entirely with the theoretical value. This method is not affected by the presence of Cl-, Br-, and I2, so that it is considered to be suitable for determination of a trace (0.001-0.0001M) of I- in the presence of those halogens. However, the process is affected by the presence of alcohol and the method cannot be used for determination of preparations containing alcohol.
