individual investigation?

Question

hi,i'm also doin a-level chemistry salters and i am currently doing my individual investigation on the iodine clock,plsmcould someone guide me on how to start and especially the hazards involved in using sodium thiosulphate,potassium iodide and potassium peroxodisulphate

Answer 1

The Iodine clock reaction or Landolt reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered in 1886 . Two clear solutions are mixed and at first there is no visible reaction, but after a short time delay, the liquid suddenly turns dark. The iodine clock reaction exists in several variations.

I know the hydrogen peroxide one:

This reaction starts from a solution of hydrogen peroxide with sulfuric acid. To this is added a solution containing potassium iodide, sodium thiosulfate, and starch. There are two reactions occurring in the solution.

In the first, slow reaction, the triiodide ion is produced .
H2O2(aq) + 3 I-(aq) + 2 H+ → I3- + 2 H2O.
In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate.
I3-(aq) + 2 S2O32-(aq) → 3 I-(aq) + S4O62-(aq)
After some time the solution will rapidly change color to a very dark blue, almost black.

When the solutions are mixed, the second reaction causes the triiodide ion to be consumed much faster than it is generated, and only a small amount of triiodide is present in the dynamic equilibrium. Once the thiosulfate ion has been exhausted, this reaction stops and the blue color caused by the triiodide - starch complex appears.

Anything that accelerates the first reaction will shorten the time until the solution changes color. Increasing the pH, or the concentration of iodide or hydrogen peroxide will shorten the time. Adding more thiosulfate will have the opposite effect; it will take longer for the blue color to appear.

Tips:
If u want a dark purple colour use more starch.

BE CAREFUL WITH H2O2.
Avoid contact with skin.

The rest of the chemicals if dilute enough are not that harmful or carcinogenic.

Answer 2

To start the reaction a solution of hydrogen peroxide with sulfuric acid. To this is added a solution containing potassium iodide, sodium thiosulfate, and starch.
In the first, slow reaction, the triiodide ion is produced .
H2O2(aq) + 3 I-(aq) + 2 H+ → I3- + 2 H2O.
In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate.
I3-(aq) + 2 S2O32-(aq) → 3 I-(aq) + S4O62-(aq)

After some time the solution will rapidly change color to a very dark blue, almost black.

When the solutions are mixed, the second reaction causes the triiodide ion to be consumed much faster than it is generated, and only a small amount of triiodide is present in the dynamic equilibrium. Once the thiosulfate ion has been exhausted, this reaction stops and the blue color caused by the triiodide - starch complex appears.

Anything that accelerates the first reaction will shorten the time until the solution changes color. Increasing the pH, or the concentration of iodide or hydrogen peroxide will shorten the time. Adding more thiosulfate will have the opposite effect; it will take longer for the blue color to appear.

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Dangers:
There should be no dangers. They arnt carcinogenic and may only cause mild irritation.