About investigation of the Order of...Iodine with Propanone

you know that the reaction is acid catalyst.
so when a alkaline solution such as sodium bicarbonate
is added , the reaction is stopped.
there are several time intervals you want to measure,
say, 5mins , 10 mins , 15mins and 20mins.
at the four intervals, you transfer some solution out of the
conical flask. you want to test how much the iodine is reacted.
so you must stop the reaction . otherwise the reaction will go
on without stopping. OK?