The metal ion indicator xylenol orange (Table 11-3) is yellow at pH 6 ( max = 439

The metal ion indicator xylenol orange (Table 11-3) is yellow at pH 6 (λ_max = 439 nm). The spectral changes that occur as VO²⁺ is added to the indicator at pH 6 are shown here. The mole ratio VO²⁺/xylenol orange at each point is

Suggest a sequence of chemical reactions to explain the spectral changes, especially the isosbestic points at 457 and 528 nm.

Table 11-3

Transcribed Image Text:

Trace Mole ratiTrace Mole ratio Trace Mole ratio 0.60 0.70 0.80 0.90 1.0 12 13 1.5 14 2.0 15 3.1 16 4.1 1.3 0.10 2 0.20 0.30 0.40 5 0.50 4 10 16 0.1 Absorbance unit 13 12 600 500 Wavelength (nm) 400