Approach to Accurate Models for Investigating the Chemical Processes in Non- Constant Ionic Strength

A proper chemical model should be close to the behavior of the system under study. In solutions which contains electronic charges for calculating the equilibrium parameters, using activities leads to somewhat better results that the use of concentration. So it seems necessary providing a more complete model to the apparent model. In this study, the effect of ionic strength of a solution on equilibrium systems has been studied. To investigate the effect of solution ionic strength, Titration of Bismuth(Bi+3) with Chloride(Cl-) was selected and spectrophotometric data is recorded [1]. Data is fitted two model (concentration and activity-base model). Calculated equilibrium constant of two model are different (due to the ionic strength of the solution). Also the effect of changing ionic strength of solutions on equilibrium perturbation, it could be a novel method to survey the equilibrium systems which are contains electrically charged species. For this purpose, we select Bromocresol green(BCG) dye and titred with electrolyte(NaCl) and spectrophotometric data is recorded. Data fitted to activity based model and thermodynamic equilibrium constant calculated (pKa=4.79±0.005). this result agree with that was reported in literature (pKa=4.91±0.02) [2]. Also in this research, we investigated resistance of electrolyte (which is used to stabilize ionic strength) against the change in ionic strength solution. So we indicated the required electrolyte concentration to fix ionic strength solution.