Spectrophotometric determination of chlorate ion with Methyl Orange

Abstract

Under suitable high chloride ion concentration in an acidic solution {(37) MH₂SO₄}, chlorate ion reacts with chloride ion to form chlorine which reacts quantitatively with Methyl Orange to decrease the absorbance (at 504 nm). Therefore, the decreased absorbance of Methyl Orange by this reaction was used to determine the chlorate ion concentration. Analytical procedure is as follows. Mix 1 ml of the sodium chlorate solution {(1×10^-51×10^-4)M} with 10 ml of 6.3×10^-3 g/l Methyl Orange solution which contains 6 M sulfuric acid and 0.3 M chloride ion. After shaking for about 20 min, measure the absorbance at 504 nm against the reagent blank. The molar absorptivity of Methyl Orange is 4.63×10⁴ l mol^-1 cm^-1 at 504 nm and is constant at room temperature for at least 2 days. Less than 5×10^-3 M of Mg²⁺, Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Al³⁺, Mn²⁺, Fe³⁺, Cu²⁺ and of SO₄^2-, CO₃^2-, PO₄^3-, F^-, ClO^-, ClO₂^-, ClO₄^- do not interfere with analysis, where in the solution containing ClO^-, ClO₂^-, ClO₃^- and ClO₄^-, the chlorate ion can be determined after reducing ClO^- and ClO₂^- with KBH₄.