Chemistry- Iodine/ Thiosulfate Clock Reaction

Hi guys, i'm doing the iodine clock reaction for my advanced higher investigation. I understand the theory of kinetics and what not, but am extremely confused as to what to actually do in the procedure. The equipment I have been given is:
1% starch
0.001M ammonium molydbate-7-water
ammonium molydbate
Starch
10 Vol (3%) hydrogen peroxide
0.1 mol/l potassium iodide
1M sulphuric acid
0.1 M sodium thiosulfate

I have to do a variety of experiments which I think are:

1)Effect of hydrogen peroxide/ potassium iodide concentration on reaction rate
2) Effect of tempreature of reactants on reaction rate
3) Effect of catalyst (ammonium molybdate) on reaction rate

Are these right? And what volumes and concentrations do I use in the experiments ?I have also been told to mention the Arrhenius equations and activation energy.

Any help would be massively appreciated. Thanks so much guys!!

Reply 1

TSR Jessica

19

Sorry you've not had any responses about this. :frown:

Why not try posting in a specific subject forum- you might have more luck there.

Here's a link to our subject forum which should help get you more responses. :redface:

Reply 2

User947387

17

Original post by MedicBoy98

Hi guys, i'm doing the iodine clock reaction for my advanced higher investigation. I understand the theory of kinetics and what not, but am extremely confused as to what to actually do in the procedure. The equipment I have been given is:
1% starch
0.001M ammonium molydbate-7-water
ammonium molydbate
Starch
10 Vol (3%) hydrogen peroxide
0.1 mol/l potassium iodide
1M sulphuric acid
0.1 M sodium thiosulfate

I have to do a variety of experiments which I think are:

1)Effect of hydrogen peroxide/ potassium iodide concentration on reaction rate
2) Effect of tempreature of reactants on reaction rate
3) Effect of catalyst (ammonium molybdate) on reaction rate

Are these right? And what volumes and concentrations do I use in the experiments ?I have also been told to mention the Arrhenius equations and activation energy.

Any help would be massively appreciated. Thanks so much guys!!

As the concentration increases, so does the rate of the reaction.

This experiment involved the combining of several reactants with a visible colour change from colourless to black observed.
3I-(aq)+ H2O2 (aq)+ 2H+(aq)I3(aq)+2H2O (I)
I3-(aq)+2S2O32-3I-(aq)+S4O62-

So, when the iodide ions are exposed to the acidified hydrogen peroxide, they became oxidised and when they WERE oxidised, they formed triiodide ions.

But the newly formed activated complex degraded back because to the thiosulphate ions, via reduction reaction.

Oxidation/Reduction went back and forth until the stockpile of the thiosulphate ions were consumed entirely.

So, without the thiosulphate ions intefering, this meant that the triiodide ions could then freely react with the starch complex.

Characteristic and instantly identifiable blue-black coloured complex. In this reaction, the exposure of the triiodide ions to the starch complex also elicited this same characteristic colour change.

Therefore, an increase in the concentration of one (or more) of the reactants involved in a chemical reaction will increase the number of successful collisions between the particles of the reactants which in turn will as per the Arrhenius equation, result in a faster rate of reaction. This is the basis of “collision theory.”

(edited 8 years ago)

Reply 3

MedicBoy98

OP

2

Thanks for the reply. I found another set of equations:
H2O2 + 2I− + 2H+ → I2 + 2H2O

2S2O32− + I2 → S4O62− + 2I−

Which one is the right one?

Reply 4

Trhoul

2

when discussing how the concentration of KI affects the reactions rate, both of them are relevant. the first equation will be sped up due to collision theory directly. the second equation carries out until all of the sodium thiosulfate has been reacted with, this allows the iodine molecules to react with the starch. the starch simply shows when the reaction has been carried out. it allows for the repeats of this experiment to be timed and compared.

Chemistry- Iodine/ Thiosulfate Clock Reaction

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