SPECTROPHOTOMETRIC AND POTENTIOMETRIC STUDY OF TETRAVALENT VANADIUM-PYROGALLOL RED CHELATE

Vanadium(IV) forms a violet chelate (λmax540 mμ) with pyrogallol red at pH 4.4. The Sandell's sensitivity of color reaction is 0.04 μg/cm2. The chelate is stable between pH 3.5 to 5.5. The composition of the chelate VO2+:(PGR)2 was established by the continuous variation and mole ratio methods using absorbance data. The conditional stability constants were calculated by continuous variation (using nonequimolar solutions) and mole ratio methods. Stepwise stability constant values were evaluated by Bjerrum and Calvin pH-titration technique as log K1 = 9.5 and log K2 = 4.0. Ringbom optimum range for accurate colorimetric analysis and photometric error in absorbance measurements were also determined. © 1969.