Log in

View Full Version : Iodine clock reaction with S2O3 ion


Olya315
Jul 15, 2007, 02:47 PM
In the iodine clock reaction with S2O3 ion I have found that one of the exponents in the reaction rate is 1.55. Can I round it to 2? Or shoud I write it as a fruction 3/2?

I know that reaction rate can be a fraction. But it is a fraction in this case?

Thank you! :)

mirna sherry
May 8, 2009, 03:19 PM
For sure it can be 1.55 you must leave it as it is.

mirna sherry
May 8, 2009, 03:28 PM
Thank you but iodine doesn't react with oxygen

Perito
May 8, 2009, 05:14 PM
This is in the wrong thread. Here is the original thread.

https://www.askmehelpdesk.com/chemistry/why-after-titration-s2o3-2-using-starh-indicator-blue-reappears-351397.html

Iodine certainly won't react with oxygen, but will it react with iodide? It certainly doesn't do it very often, but it can happen (the Winkler test requires a Manganese catalyst). Oxygen is a sufficiently strong oxidizer.

Winkler test for dissolved oxygen - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Winkler_test_for_dissolved_oxygen)

Time-resolved reaction of oxygen(1.DELTA.) with iodide in aqueous solution - The Journal of Physical Chemistry (ACS Publications) (http://pubs.acs.org/doi/abs/10.1021/j100334a026)

2I^- \rightleftharpoons I_2 + 2 e^- E = - 0.54 volts

O_2 + 4H^+ + 4e^- \rightleftharpoons 2H_2O E = 1.23 V

ΔE = +.69 volts

You can see that the electrochemical potential is there (which says nothing about kinetics). In addition, it only takes a tiny amount of iodine to turn starch blue. The last thing is that it's the only thing I can think of that's present that could oxidize iodide to iodine. Iodine has to be present or the starch wouldn't turn blue. I'm open to other suggestions.