I mixed 5ml H202 with 5ml KI with 5ml H2SO4 wit Na2So2O3 with 50ml. Now I am trying to figure out all the elementary steps for this reaction. A starch was added in this mixture to measure the reaction time with the thiosulfate and the I2. I was just wonder if anyone could give me all the elementary steps for this reaction?

Question

I mixed 5ml H202 with 5ml KI with 5ml H2SO4 wit Na2So2O3 with 50ml. Now I am trying to figure out all the elementary steps for this reaction. A starch was added in this mixture to measure the reaction time with the thiosulfate and the I2. I was just wonder if anyone could give me all the elementary steps for this reaction?

I came up with this but it is wrong or incomplete.

H2O2+2I^-+2H^+ ---> I2 + 2H20
I2+I^- ----> I3^-
I2+2S2O3^2- ---> 2I^- + S4O6^-2
STARCH + I2 ---- BLUE

Now what steps am I missing exactly?
Any help would be appreciated.

Answer 1

That looks ok to me. Personally, I would not have used the second step, although it is correct as you have it. However, I see it used in most of the modern texts; it may be that if you are being taught to use it that you didn't show it with the I3^- + 2S2O3^-2 ==> 3I^- + S4O6^-2