ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 22, Number 5
JKCSEZ 22(5)
October 20, 1978 

The reaction between iron(Ⅲ) and Xylenol Orange (XO or H6A) has been investigated spectrophotometrically. It has been established that iron (Ⅲ) and XO form two complexes with compositions iron(Ⅲ) : XO = 2 : 1 and 1 : 1. The 2 : 1 complex is stable in acidic medium containing excess of iron, and 1 : 1 complex is stable in slightly acidic medium containing excess of XO. The absorption maxima are at 590 nm (2 : 1) and 500 nm (1 : 1), the molar absorptivities being 3.18 ± 0.04 × 104 and 1.32 ± 0.03 × 104 respectively. The stability constants of two complexes studied by varying pH are log β21 = 18.69 ± 0.03, log β212 = 42.08 ± 0.09, log β11 = 4.17 ± 0.04, and log β113 = 34.47 ± 0.07.