Full Question : Qn8

http://www.rsc.org/images/2000_Rd%20_1_Questions_tcm18-190754.pdfAnswers (not full working though)

http://www.rsc.org/images/2000_Rd_1_Answers_tcm18-190755.pdfThing is, I'm unable to obtain the value of k as 0.112 (the given answer).

My method :

Since order of reaction wrt to I3- is 1, and since

rate = c [I3ā]^1 where c = k [H3AsO3]^1 [H+]^-1 [Iā]^-2,

accordingly using c = ln2/t(1/2) (for any one of the 4 Runs) and substituting both the value of c, as well as the molarities of the other species (for that particular Run) into the equation

c = k [H3AsO3]^1 [H+]^-1 [Iā]^-2

we should be able to obtain the value of k, which based on the 4 Runs, are approximately 0.12 to 0.13 (to 2 sf), but the given answer is 0.11 (to 2 sf).

Any assistance would be much appreciated.