The measuring method
The experiments are conducted in a thermostated cell placed on a magnetic stirrer
(Fig. 1). A total of 55 mL of solution A (containing Na2S2O3, KI, KNO3 and starch) is
placed in the cell and 5 mL of solution B (containing Fe(NO3)3 and HNO3) is placed
in the syringe. Solution A is stirred by a magnet. Solution B is injected into solution A
and a stop watch is started at that point. Time is recorded at the moment the solution
suddenly turns dark blue. The experiment is conducted three times for each
concentration.
The ionic strength is set to Ic = 1.0 mol L-1 by KNO3 and HNO3 in order to keep it
constant during the course of reaction.