The indicator changed color when all the thiosulfate ions, S2O32-, were used up. Upon the instant the solutions were mixed, you calculated a molarity of S2O32- (from Q 9). Since the concentration of thiosulfate changed from this value to zero this is the value of ?[S2O32-]. What is the value of ?[I2] at the point of the color change for each of the runs? (Show your work) Consider the balanced reaction for the clock step: I2(aq) + 2 S2O32-(aq) ? 2 I-(aq) + S4O62-(aq) ?
(Q9) Upon the instant the solutions are mixed, what is the concentration (in M) of thiosulfate for all of the trials? (Show your work)
a)Which pair of trials could be used to determine the order for Iâ? Justify your choice.
b)How would you determine the order for H+? Be as specific as possible.
c)What would be the value for the initial rate if 5 mL KBrO3 solution, 5 mL KI solution, 5 mL Na2S2O3 solution, 10 mL KCl solution, 15 mL pH = 4.74 buffer solution, and 1 drop of 1% starch solution were used?
d)Why do Trials 1 and 4 have the same initial rate?
e)What time was required for the color change to occur in Trial 1?
f)What was the purpose of adding 5 mL of 0.040 M KCl in Trial 2?
g)How would you experimentally verify that KCl does not cause the color change from colorless to blue? Be as specific as possible.
