You can get the concept of: Strong and weak acid dissociation constants and the value of pKa, equation Henderson-Hasselbalch, Lambert's law, Photometry.
Principle: Blue Thymol, color indicator, behaves as a weak acid in aqueous solutions, whereby the ionized and unionized form exhibit absorption maxima at different wavelengths of the visible region of the electromagnetic spectrum. Ka or pKa values of indicators that characterize the equilibrium dissociation may thus be determined using photometric measurements in the visible spectral region.
