Answer to Question #140031 in General Chemistry for Nathaniel

Question

. Use the rate law to explain quantitatively how decreasing the iodate ion concentration
affects the rate of the iodine clock reaction

Answer 1

The iodine clock reaction involves redox reagents and iodate ion in the presence of starch. Two reactions co-occur in the solution. The first reaction is slow, while the second is fast.

In the first, iodine is formed:

H₂O₂ + 2I⁻ + 2H⁺ → I₂+ 2H₂O

In the second, iodine is re-converted to two iodide ions by the thiosulfate:

2S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2I⁻

After some time, the solution changes color to a very dark blue, almost black. The rate law maintains that decreasing the iodate ion concentration will shorten the iodine clock reaction time. Therefore, anything that hastens the first reaction will shorten the time until the solution changes color.