Okay, so I did a lab recently where we are to determine the Rate Law for a mixture of KI, starch, Na2S2O3, H202 and enough distilled water to make sure total solution volume is equal for all experiments. So when this thing starts to go we get I2 +2S2O4--->2I + S4O6, so when doing the calculations do we use 1/2M of KI for determining the rate? Now where does the I2 come from? When KI hits the solution doesn't it dissociate into negatively charged I ions? I wish they gave more detail.