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Topic: Function of starch solution(1)  (Read 19726 times)

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Offline kylon

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Function of starch solution(1)
« on: July 17, 2007, 07:48:16 PM »
When having an experiment "rate law of an iodine clock reaction", a starch solution is added. What is the function of starch solution?
Thank for help first...

Offline Yggdrasil

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Re: Function of starch solution(1)
« Reply #1 on: July 17, 2007, 07:58:39 PM »
The starch is likely acting as an indicator for the presence of triiodide ion.  Starch and triiodide form a complex which gives the solution a deep blue-black color.

http://en.wikipedia.org/wiki/Iodine_clock_reaction

Offline kylon

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Re: Function of starch solution(1)
« Reply #2 on: July 18, 2007, 05:04:14 AM »
Sorry, I miss some important things.
The experiment is using sulfuric asid, potassium iodine, thiosulfate, starch solution and distilled water.

The equations are:

H2O2 + 2I- + 2H3O+
---> I2 + 4H2O

I2 + 2S2O32- ----> S4O62- + 2I-

there are no triiodine ion.



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Offline Borek

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Re: Function of starch solution(1)
« Reply #4 on: July 18, 2007, 06:59:28 AM »
I2 + 2S2O32- ----> S4O62- + 2I-

there are no triiodine ion.

Yes, there is :) It is present in the solution whenever you have both I2 and I-

I2 + I- <--> I3-
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