Permanganate-Oxalic Acid Reaction: A Modified Approach Using Surfactant Solutions In the regular curriculum, the permanganate-odic acid reaction is carried out at about TO O C . Here, we report a simple mndificarionof this procedureemploying surfactant mrdia that enable the quirk andquanritative determination of KMnO,at ruom temperaturr. The mechanismof catalyris by surfartan~siadifferent from that rffrcred hy theaddition of Mn(I1) or ascorbic acid.' The title reactian was attempted in presence of the surfactnnts, sodium laurylsulfate (NaLS) and eetyltrimethyl&m monium bromide (CTAB) as described below. Procedure 1 A solution containing 1.32 X M KMnO* 5.70 X M oxalic acid, and the surfactant NaLS (7.0 X 10-4 M) or M) were prepared. No acid was added. This solution was left a t room temperature. The pink color of the CTAB (1.0 X solution disappeared completely in both the cases (in presence of NaLS as well as CTAB) in 1h, indicating the completion of the reactian. However, a similar reactian in the absence of any surfactant did not go to completion even after 3 h. Though the above experiment hrings out the catalytic power of the surfactants on this reaction, the time required for the completion of the reaction (60 min) is too long for the reaction to be included conveniently in the regular curriculum. Therefore, the reaction conditions were modified by studying it in presence of several concentrations of any one of the surfactants either individually or in combination with sulfuric acid. Finally, procedure 2, described below, was found to be satisfactory for the estimation of KMn04 both in terns of the time required and accuracy. Procedure 2 A standard oxalic aeid solution (20 mL) was mixed with sulfuric acid and one of the surfactant solutions in a conical flask.The volumes of the acid and the surfactant solutions were so chosen that the resulting solution would contain 1.0 M M NaLS or 2.0 X M CTAB. After 1min. this solution was titrated (without heatind HISOL and 1.0 X .~~. ~ .with . the test solurionofporassium permanpanare. No difficulty w s s e n c o u n r ~ r ~~n dfixing Iheendpuint. ~ i r r a t i o m were rep~ntedwrth oxalic acid solutions of different concentrations ranging from 0.02 to 010 M. Kach titration was done at least thrrce and found to be repraducible. In each experiment, the concentration of KMn04 calculated from the titre was in very good agreement (within 0.5%) with the expected value. The advantage of this procedure are: (1) it does not require heating, (2) the titration can he carried out almost immediately after mixing the reagents, and (3) the reaction is quantitative. ~~
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' Datta. M.: Ameta, S. C.; Pande. P. N.: Gupta. H. L.: Bokadia. M. M. J. Chem. Educ. 197% 56, 659. Author 10 whom correspondence shouM be addressed. D. Suresh Ponraj, R. Venkataraman, and P. S. Raghavan2 Madras Christian College Tambaram, Madras-600059, India
Volume 67
Number 7
July 1990
821
