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The kinetics of the reaction between colloidal manganese dioxide (obtained by reduction of potassium permanganate with sodium thiosulfate) and formic acid at 25°C and constant ionic strength in aqueous perchloric acid solution were studied in the presence of surface active agents, such as cationic cetyltrimethylammoniumbromide (CTAB), anionic sodium lauryl sulfate (SDS), non-ionic Triton X-100. The reaction rate was followed spectrophotometrically by measuring the changes in absorbance at 500 nm. The results were analyzed by means of the fixed time method. Cationic surfactants cause flocculation of the oppositely charged colloidal MnO 2 and could not be used, whereas anionic micellar systems were found to be ineffective on the reaction rate. No noticeable effect of SDS on the reaction rate was observed, even at high concentrations. This reaction was found to be accelerated by non-ionic micelles of Triton X-100. The reaction was first-order with and without surfactants, and the rate constant, k , increased as Triton X-100 concentration increased and reached a plateau at higher concentrations. |
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