Chapter 5, Problem 124RQ

In June 2002, the Department of Health and Children in Ireland began a program to distribute tablets of potassium iodate to households as part of Irelands National

Emergency Plan for Nuclear Accidents. Potassium iodate provides iodine, which when taken during a nuclear emergency, works by “topping off “ the thyroid gland to prevent the uptake of radioactive iodine that might be released into the environment by a nuclear accident. To test the potency of the tablets, a chemist dissolved one in 100.0 mL of water, made the solution acidic, and then added excess potassium iodide, which caused the following reaction to occur.

${\text{IO}}_{\text{3}}{}^{\text{-}}{\text{+8I}}^{\text{-}}{\text{+6H}}^{\text{+}}\to {\text{3I}}_{\text{3}}{}^{\text{-}}{\text{+3H}}_{\text{2}}\text{O}$

The resulting solution containing ${\text{I}}_{\text{3}}$

^- was titrated with 0.0500 M ${\text{Na}}_{\text{2}}{\text{S}}_{\text{2}}{\text{O}}_{\text{3}}$ solution, using starch indicator to

detect the end point. (In the presence of iodine, starch turns dark blue. When the ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{\text{2-}}$ has consumed all of the iodine, the solution becomes colorless.) The titration required 22.61 mL of the thiosulfate solution to reach the end point. The reaction during the titration was

${\text{I}}_{\text{3}}{}^{\text{-}}{\text{+2S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{\text{2-}}\to {\text{3I}}^{\text{-}}{\text{+S}}_{\text{4}}{\text{O}}_{\text{6}}{}^{\text{2-}}$

How many milligrams of ${\text{KIO}}_{\text{3}}$ were in the tablet?