Question

experiment 24 a kinetic study the iodine clock reaction

Name: Experiment 24 Partner: Data and Observations Trial Time Elapsed (sec) Variation from Trial #1 Number of Times Faster Than Trial #1 (time/time) room temperature 93 - 1x T= 25 °C [1") doubled [Bro, doubled [H+] doubled temperature increased T= 35 oC

Answer 1

Here the reactions are

$BrO_3^-(aq)+6I^- (aq) +6H^+(aq)\rightarrow 3I_2(aq) + Br^{-} (aq)+ 3H_2O(l)$

The liberated iodine reacts with thiosulphate as

612(aq) + S20 (aq) +1 +S402 (aq)

First reaction is slow and second one is faster, so iodide ion is regenerated and this will again react with bromate ion (BrO3-) and Iodine is liberated which again react with thiosulphate ion (S2O32-) , this goes on and on unless all thiosulphase is used up.

After all thiosulphate is used up, Iodine I2 will react with starch and turn blue $I_2 + Starch \rightarrow$ Blue complex which indicates reaction is completed.

So, in your data table only one column is left blank and which suggest data is to be filled by dividing time of first trial by subsequent trials $(Time_1/Time_n)$

Trial	Time elapsed (sec)	Variation	Number of times fater than trial 1 $(Time_1/Time_n)$
1	93	T = $25^0C$	1$\times$
2	72	$[I^-]$ doubled	1.29$\times$
3	58	$[BrO_3^-]$ doubled	1.6$\times$
4	36	$[H^+]$ doubled	2.58$\times$
5	50	T=$35^0C$	1.86 $\times$

Thus it indicates increasing concentration of species involved and temperature increases the rate of reaction.