Extra Practice with Redox Titrations: Stoichiometry for Standardization of Sodiu

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Extra Practice with Redox Titrations: Stoichiometry for Standardization of Sodium Thiosulfate. Highly pure solutions of the titrant sodium thiosulfate, Na2S203, are difficult to prepare and subject to decomposition over relatively short periods of time. Therefore, it was necessary for our lab technicians to standardize (determine the exact molarity of) the sodium thiosulfate solution supplied to you. Standardization was accomplished by using the Na2S203 solution to titrate an accurately known number of moles of potassium iodate, KIO3. Potassium iodate is used because it is a primary standard, a non-hygroscopic (non- water adsorbing) substance of high purity and large molar mass. These qualities make it possible to prepare a KIO3 solution of accurately known concentration. The standardization of the sodium thiosulfate solution involves a two-step, indirect redox titration analogous to that used the analysis of the diluted bleach solution. (a) The first redox reaction takes place in the flask before the titration: the I03 and the excess I produce 13 in acidic solution. Balance this redox reaction using the half-reaction method as outlined in your lab manual (Expt 3 Introduction). Hints: 1. Note that this redox reaction yields the same product for both the oxidation and reduction half-reactions. 2. Reduce all coefficients to the smallest possible integers. Enter the correct coefficients in the boxes below. (Note that coefficients of "O" or "1", whenever required to balance the equation shown, must be entered here in the appropriate box(es), in order for this LON-CAPA problem to work. Normally one does not write equations this way. (see below) (Eqn. 3) 103_ + l-+ H+ 13_ + H2O

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Extra Practice with Redox Titrations: Stoichiometry for Standardization of Sodiu

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