Originally posted by pantone159
Shakhashiri, Chemical Demonstrations, Vol 4, 10.1 has a discussion of this reaction.
According to this, the empirical relationship between the clock period and initial concentrations of HSO3- and IO3- ions, at 25 C, and 'with no added
acid' is:
P = (0.003 s-mol-mol/liter-liter) / ( [IO3-]0 [HSO3-]0 )
So for initial iodate = 0.025 M and initial bisulfite = 0.013 M, this gives about 9 sec. (I calculate 9.23 sec). It does mention that if there are
more than 3 times as many bisulfite as iodate, there won't be a color change and the equation is not applicable.
I'm not sure this equation matches your results, however.
I wouldn't add sulfate ion, it appears in the reaction equations so I would expect it to interfere with the timings. |