Question
in this rxn, what is an intermediate species? is it I-?
how do I know if it's intermediate species?
ieuavelage Pate as being equal to the initial nStantaneous rate The rate of the reaction will be measured indirectly by running a second reaction known as a clock reaction, simultaneously along with the reaction of interest. The clock reaction must be inherently fast relative to the reaction of interest and it must consume at least one of the products of the reaction of interest. In this case the parallel reactions are the following 61 (aq) + BrO, (aq) + 6 H, (aq) 312 (aq) + Br(aq) + 3 H2O (1) slow (clock reaction) 31, (aq) + 6 S,012-(aq)-> 6 I. (aq) + 3S,062-(aq) fast Note that since the clock reaction is relatively fast, the l2 (aq) will be consumed by the clock reaction as quickly as it can be produced by the reaction of interest thus holding the 2 concentration at a very low value close to zero. Only after the S203 has been entirely consumed will the concentration of l2 start to increase. After the S203 has been consumed the concentration of 12 will increase rapidly allowing the l2 to react with a starch indicator resulting in the solution turning to a deep blue color In this experiment you will measure the time required for the solution to turn blue. This is essentially the amount of time required for all of the S2032 to be reacted Inspection of Table 1 shows that the number of moles of S2032 is the same for all reaction mixtures and is relatively small compared to the numher of mol
Explanation / Answer
I2 is the intermediate. In any reaction the intermediate is formed in a slow step only to be consumed fast in a rapid step later such that it is just a short lived species as an intermediate.
In the first reaction, iodine is produced (slow)
In the second iodine is converted to iodide ions by the thiosulfate
S2O32 + I2 S4O62 + I (fast)
change incolor to a very dark blue is observed when we have excess I2 which forms complex with starch.
So I2 is the intermediate.
