Question

METHOD 1- Visual clock reaction. The solutions for each of the kinetic runs are given in the table on the next page. The sodium thiosulfate (Na S,O,) is used as part of an indicator system (a purple color will form) to enable you to determine the time required for the reaction to occur for each kinetic run. As the amount of product formed in each case (SO) will be the same, the relative rates of reaction will be inversely proportional to the reaction time. For example, a reaction that takes 25 seconds has twice the rate of one that takes 50 seconds. Because of the proportionality, for the analysis today, it will be possible to substitute the inverse of the time (1/t) for the actual rate of the reaction. To study the effect of reactant (T and S,0,2) concentrations on reaction rates, the reactant concentrations will be decreased. The simplest method for achieving this goal is to use a smaller amount of one of the reactants while keeping the total volume constant by replacement with water containing a substance that will not affect the reaction but that will maintain the same concentration of ions. The solutions of KCl and K,SO, are used for this purpose.

Answer 1

4. Sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color.

5. Potassium chloride (KCl) and potassium sulfate (K₂SO₄) are used to maintain the ionic strength of the solutions and are used as fillers to maintain a constant volume to allow a decrease in the concentrations of I-and S2O82-. The fillers have no drastic or influential effects on the reaction due to have anidentical net ionic strength as water.

6.  CuSO4 serves as a catalyst and speeds up the reaction by providing an alternative pathway which requires lower activation energy.