Question

What is the reaction of ozone and potassium iodide?

Answer 1

We need to know that the ozone is a molecule of oxygen having three oxygen atoms while potassium iodide is the compound having formula KI containing two atoms that is potassium and iodine. When iodine is involved in reactions, two reactions can be considered as either isometric or iodometric reactions.

Complete answer:
So we will see now the reaction between potassium iodide and ozone:
$2KI + {O_3} + {H_2}O \to {\text{ }}{I_2} + {O_2} + 2KOH$
This reaction represents a redox reaction as oxidation and reduction are taking place simultaneously. In this reaction potassium iodide or iodide ion is oxidized to iodine molecules while ozone gets reduced to oxygen. Since ${O_2}$ is much less active than ${O_3}$, the reduction just stops right there for kinetic reasons. The color of potassium iodide is dark pink or purple in color. As a medication it is used to treat hyperthyroidism, in radiation emergencies, and to protect the thyroid gland when certain types of radiopharmaceuticals are used.
The reaction equation does not really give information about the full mechanism, but one possibility is that the ozone is first reduced to ozonide ion, which is known in compounds with heavier alkali metals like potassium,; then the ozonide ion disproportionate to give diatomic oxygen and the reducing agent is not specified as iodide ion. Any mild reducing agent can act similarly.
${O_3} + {e^ - } \to {O_3}^ -$
${O_3}^ - + {e^ - } + {H_2}O \to 2O{H^ - } + {O_2}$

Note:
We have to remember that the iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant. This absorption will cause the solution to change its color from deep blue to light yellow when titrated with standardized thiosulfate solution.