In the present paper, a sensitive, fast and suitable method for calculating dissociation constant (pKa) value of acid alizarin violet N (AVN) is proposed. The study was performed in the absorption spectra at 190–700 nm intervals were recorded. The dissociation constant of AVN at pH range 1.50–10.00 and at constant ionic strength 0.1 mol L-1 and 25ºC were determined using DATa Analysis (DATAN) program using spectrophotometric titration data. The calculated pKa of AVN in water was 6.25
