Abstract
The dissolution kinetics of colloidal MnO2 in aqueous hydrochloric acid is studied at 298 K by spectrophotometric methods. The decay profile of MnO2 monitored by measuring absorbance due to MnO2 at 390 nm was exponential. As the hydrochloric acid concentration was increased from 1.26 to 5.03 M, the dissolution rate of MnO2 to Mn(II) species decreased. The reaction followed fractional order kinetics with respect both to MnO2 and HCl concentrations. The average oxidation state approached a value of +2 indicating that HCl reduced Mn-species to Mn(II) species. Mechanism based on the observed kinetics has been proposed and discussed.