What is the iodine clock reaction system and what is the propose of doing experiments?

Answer 1

The purpose of doing this experiment is generally as an introduction to the concept of kinetics in chemistry. Kinetics is studying the RATES OF REACTIONS.

The reaction system consists of peroxide (H₂O₂), Iodide (I^-), acid (H⁺), thiosulfate (S₂O₃^2-) and starch. The reaction occurs in 2 steps as follows:

H₂O₂(aq) + 2I^– (aq) + 2H⁺ (aq) → I₂(aq) + 2H₂O(l) ... reaction 1

2S₂O₃^2–(aq) + I₂(aq) → S₄O₆^2–(aq) + 2 I^– (aq) ... reaction 2

As the iodine (I₂₎ is formed in reaction 1, it reacts with the thiosulfate (S₂O₃^2-) in equation 2 to form S₄O₆^2- ions and I^- again, which then goes back to react again with the H₂O₂ (reaction 1), thus producing more I₂

When all of the S₂O₃^2- in reaction 2 is used up, the free iodine that remains in solution reacts with the starch to form a bluish black solution. The time it takes for this entire reaction to take place and for the blue-black color to appear can be changed by simply changing the concentration of the I^- in reaction 1. If you double the concentration, the time should take about 1/2 as long and if you cut the [I^-] in half, the reaction should take about twice as long. This has to do with the fact that reaction 1 is rate limiting and is first order with respect to [I-]