Determination of the lron(III)-Thiocyanate Reaction Equilibrium Constant using digital images

The reaction Fe3+ + CSN- !::; Fe(SCN)2+ is simple and easy to observe, because Fe3+ has a slight yellow color, CSN- is colorless and Fe(SCN)2+ are deep blood-red (Amax = 447 nm), the determination of equilibrium constant of this reaction is presented in many laboratory manuals. Fe(SCN)2+ concentrations were determined using a calibration polt, then, the equil ibrium constants were measured in mixtures of Fe3+ and SCN-. For the colorimetric determination of Fe(SCN)2+ absorbance at 447 nm were measured in each solution. Fe(SCN)2+ concentrations are also determined using digital images, where solutions were placed in a 96 micro-well plate and a digital image obtained using a flatbed scanner, R (red) values of each well were extracted simultaneously using lmageJ's plugin ReadPiate. In 2017, this laboratory experiment was carried out in Universidade Regional de 8/umenau with chemical engineering, students. It was typically finished in approximately 150 mim with 15 students working in groups of three. The goal of this project was to develop a simple spectrophotometric method based on images obtained with a regular consumer-grade computer scanner. These results would then be compared to measurements from conventional spectroscopy using oneway ANOVA. Whether there is statistical evidence that the associated population means are significantly different. Using the Analysis TooiPak in Excel, within the confidence level of 95%, we found Fcalculated = 1.33 < Fcritical = 1.94 showing that results obtained with both methods were equivalent at a 95% confidence interval.