Determination of the acidity constants of neutral red and bromocresol green by solution scanometric method and comparison with spectrophotometric results

AbstractIn this study, we applied the solution scanometric method as a new, simple, fast and inexpensive method for estimating the acidity constants of neutral red (NR) and bromocresol green (BCG) indicators in pure water and an ionic strength of 0.1 mol L−1 (KNO3).The method is based on scanning cells containing the indicator solution with a scanner, and analyzing the color of each cell with a software written in visual basic (VB 6) media to red, green and blue values. The cells were made by making holes in the Plexiglas® sheet. Also, the acidity constants of the neutral red and bromocresol green indicators were studied with spectrophotometrically. HypSpec program has been applied for the estimation of pKa values based on spectrophotometric data. The agreement between obtained pKa values by solution scanometric, spectrophotometric method and values reported in the literature demonstrates the utility of the method here used. Also the HySS 2009 program was applied for drawing of the corresponding distribution diagrams