Abstract: The oxidation of hydroxylamine by 12-tungstocobalt (Ⅲ) ate (Co(Ⅲ)W) in the acetate buffer solution has been investigated. It was found that the reaction proceeds in the presence of some metal ions, especially Fe (Ⅲ). The stoichiometry of the reaction catalyzed by Fe(Ⅲ) has been estimated bromatometrically and a kinetic study has been performed spectrophotometrically in the pH range 3.9-5.0. The empirical rate equation of the reaction is
-(d[Co(III)W])/dt=k(∑[Fe(III)]+c)∑[NH_2OH])[H~+]~(-1)
when concn. of Fe(Ⅲ) is less than 3×10~(-6)mol L~(-1). The value of k is 4.2×10~(-3)s~(-1) at 293 K and C=1.3×10~(-7)mol L~(-1). Over the temperature range 293—323 K, the values of the activation parameters of the reaction have evaluated. A mechanism of the catalyzed reaction in accordance with the rate law has been suggested.