Using Spectrophotometric Methods for Determination of the Ionization Constant of Ruthenium Red and Phenol Red Indicators

The ionization constant of Ruthenium Red and Phenol Red indicators by spectrophotometric method. The Pka of the phenol red was measured according to the half method, where the absorbance was plotted versus the PH values, the resulting curve. The data indicated that there is increase in absorbance in weak acidic media where the high value of absorbance was recorded at PH = 4&5, then the absorbance decreased for the above PH values. The Pka value of phenol red was calculated in this study by half method. So, the data recorded that the Pka = 6.7. On the other side the data showed increase the absorbance at basic media for the ruthenium red, and the Pka value was calculated by half method, the recorded that the Pka = 7.2.