The initial product from the reaction between ferrous and sulfide ions in aqueous solutions was studied using a stopped-flow spectrophotometric technique. The absorbance-time curve showed that an intermediate product formed quickly within the first few seconds of the reaction; this material subsequently decomposed slowly to other species within the following several minutes. It was more likely to form the intermediate in the pH range from 7 to 8. This suggests that the reaction between Fe2+ and HS− ions results in the formation of the intermediate product because both Fe2+ and HS− are respectively the predominant Fe(II) and S(II) species in this pH range. The absorbance at a wavelength of 500 nm varied linearly with the concentration of the intermediate, the absorptivity of which was 4800 M-1 cm-1, as determined in this study. Stoichiometric experiments, based on the continuous variation method, gave the ratio of [HS−] to [Fe2+] as 1:1 for the formation of the intermediate, which is an iron hydrosulfide of the form Fe(HS)+. Analysis of the kinetic data showed that the rate of Fe(HS)+ formation was first order with respect to both Fe2+ and HS− with a reaction rate constant of 103.81M-1 s-1. The formation constant of Fe(HS)+ was evaluated as log K = 4.34 ± 0.15 at 25°C and I = 0 from the thermodynamic analysis of the pertinent experimental data.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry