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In this study a new pH indicator, 3-benzyl-4-p-nitrobenzylidenamino-4,5-dihydro-1,2,4-triazole-5-on (BPNBAT), soluble in acetonitrile:water (1:4), was developed. The estimation of pH is possible either from the position of the absorption maxima or from the absorbance intensity at a constant wavelength. This feature allowed us to determine the basic transition range of the medium because BPNBAT is colorless at pH lower than 8.5 and showed strong yellow-green color with high extinction coefficient in the pH range of 8.5–10.1. pKa, pH at equivalent point and the molar absorptivity (in the aqueous medium at 380 nm) of BPNBAT are determined as 9.3, 8.3 and 8.8 x 103 L.mol-1.cm-1, respectively. The color change at the transition range can be attributed to the resonance structures of BPNBAT. The triazole compound was compared with thymolphthalein for accuracy test.
KEY WORDS: Acid-base indicator, 3-Benzyl-4-p-nitrobenzylidenamino-4,5-dihydro-1,2,4-triazole-5-on, UV-Vis spectrometry, Resonance, Transition point, Titrimetry
Bull. Chem. Soc. Ethiop. 2010, 24(3), 457-460.