A Rate Law and Activation Energy. 3. Part A. Table 24.1 a. When doing the kineti

Question

A Rate Law and Activation Energy. 3. Part A. Table 24.1 a. When doing the kinetic trials, Susan forgot to include the deionized water. Will this omission hasten or delay the b. When doing the kinetic trials, Oscar mistakenly omitted the sodium thiosulfate solution. How will this omission e. When doing the kinetic trials, Peyton mistakenly omitted the starch solution from the kinetic trials. How will this d. Of the three chemists above, which chemist will have the most accurate results? Explain. formation of the blue color in the trials (exclusive of Trial 6)? Explain. change the appearance of the resultant solution (from the mixing solutions A and B) from that of a correctly com- pleted experiment? Explain your reasoning omission change the appearance of the resultant solution (from the mixing solutions A and B) from that of a cor- rectly completed experiment? Explain your reasoning.

Explanation / Answer

a) In the reaction initially iodide, under acidic conditions and in the presence of molybdate catalyst, reacts with hydrogen peroxide to give iodine gas.I2 then binds with I- iodide present in the solution to form triiodide which forms blue complex with starch.

H2O2 + 2 KI + H2SO4 I2 + K2SO4 + 2 H2O        

If deionized water is not added then the concentration of KI will be high , but it will react with H2O2 in the stoichometric ratio of 1:1 only,so H2O2 works as limiting reagent as it is lesser in concentration,thereby controlling the amount of I2 produced. So the amount of triiodide will not change, but the rate of reaction will increase for

I +I-I3-   as rate of reaction is dependent on initial concentration of reactants.

Rate=k[I][I-]

As triiodide will form faster so faster will it react with starch giving blue colored complex.

b) The iodine formed in the first reaction further reacts with thiosulfate solution present in solution A giving back I- iodide,hence blue color disappears as the starch-triiodide complex is decomposed giving back I2 and i-

I2 + 2 Na2S2O3 Na2S4O6 + 2 NaI   

If thiosulfate is not added then the blue color will not disappear hence the end point of the reaction will not be detected.

c)No blue color will appear,reason explained in (b)

d)Comparatively Susan did the experiment to completion ,except that her end point will appear faster due to comparatively more concentrated solution A

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