Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H 2 SO 4 , HClO 4 , and CH 3 COOH by monitoring the formation of Cr(III)-oxalic acid complex at The effect of total [oxalic acid], [Cr(VI)], [H 2 SO 4 ], [HClO 4 ], 560 nm. and [CH 3 COOH] on the reaction rate was determined at 30ะC. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH 3 COOH] while it decreases with [H 2 SO 4 ], [HClO 4 ], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is K K rate ฯญ k [oxalic acid] [Cr(VI)] 1 ฯฉ [oxalic acid] , 1 es1 T T es1 T
where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)9 oxalic acid 1 : 1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1 : 1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C9 C bond in the 1 : 2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned.