Iron (III) Molar Extinction Coefficients in Light and Heavy Water Solutions

Abstract

Reagent-grade materials were used without purification. Both the light and heavy water were purified by distillation from an acid permanganate solution, a basic permanganate solution, and then in an all-silica system system. The redistilled water was stored in silica vessels. The light water content of the heavy water was measured by comparing its absorbancy (1) at about 16,670 A with a sample whose composition was known from mass spectrometry. The purified heavy water was determined to be 99.74 mole % D20. The acidity of each solution was adjusted to the desired value with sulfuric acid and determined by titration with standard sodium hydroxide to the phenolphthalein end point. The spectrophotometric measurements were made on a Model 11 Cary recording spectrophotometer equipped with a thermostated cell compartment. The variation of the molar extinction coefficient with temperature was determined by changing the temperature of the thermostated cell compartment and allowing 2 to 4 hours for temperature equilibrium before measuring the optical density. Two cell fillings were used for the entire temperature study-one for light water and one for heavy water. The iron (III) molar extinction coefficient in 0.4 M H2S04 light water at 25.0'C was determined by reacting iron (II) with an accurately known amount of cerium (IV) in 0.4 M H2S04 solution and measuring the optical density of the iron (III) peak. In the concentration range used there was no detectable absorp