Below are the reactions performed today: H_2 O_2(aq) + 2l^-_(aq) + 2H_3 O^+_(aq)

Question

Below are the reactions performed today: H_2 O_2(aq) + 2l^-_(aq) + 2H_3 O^+_(aq) rightarrow l_2(aq) + 4H_2 O_(1) l_2(aq) + 2S_2 O_3^2-(aq) S_4 O_6^2-_(aq) + 2l^-_(aq) I_2(aq) + l^-_(aq) + Starch (aq) rightarrow (T_3^- -Starch)_complex (aq) During your practical today you determined the rate law for Reaction 1. In your group, discuss the purpose of reactions 2 and 3. With respect to hypothetical scenarios #1 and #2, detail what would you observe: At the macro level At the sub-micro level No thiosulfate (S_2 O_3^2-) is added to the flask Answer: Neither thiosulfate nor starch is added to the flask Answer:

Explanation / Answer

#1)

If no S2O3^2- is added, oxidation of I^- doesn't take place. So correspondingly no formation of I^3- and hence no starch iodine complex formation and hence end point can't be identified.

#2)

If S2O3^2- and starch is added.Reaction stop at 1st step itself and cannot estimate I2 concentration or H2O2 concentration.

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