{"id":137,"date":"2021-06-29T17:21:22","date_gmt":"2021-06-29T17:21:22","guid":{"rendered":"https:\/\/sites.tntech.edu\/dcashman\/?p=137"},"modified":"2021-10-25T13:41:28","modified_gmt":"2021-10-25T13:41:28","slug":"chemistry-demonstration-iodine-clock-reaction","status":"publish","type":"post","link":"https:\/\/sites.tntech.edu\/dcashman\/2021\/06\/29\/chemistry-demonstration-iodine-clock-reaction\/","title":{"rendered":"Chemistry Demonstration: Iodine Clock Reaction"},"content":{"rendered":"\n

Introduction<\/strong><\/h3>\n\n\n\n

The iodine clock reaction is a classical chemical clock demonstration that displays chemical kinetics in action. It was first discovered by Hans Heinrich Landolt in 1886, so many texts may refer to it as the Landolt Reaction. In this experiment, two colorless solutions are mixed. At first, there is no reaction, and after a given period of time, the solution turns dark blue.<\/p>\n\n\n\n

This time period is termed the, “clock period”, and it is the amount of time that the mixture remains colorless until the change to dark blue. This can be calculated according to the following equation:<\/p>\n\n\n\n

0.003 sM2<\/sup> \/ [IO3<\/sub>–<\/sup>]0<\/sub> [HSO3<\/sub>–<\/sup>]0<\/sub>The procedure provided here should result in a clock period of approximately 9 seconds. Note that if the [HSO3<\/sub>–<\/sup>]0<\/sub> is three times greater than the [IO3<\/sub>–<\/sup>]0<\/sub>, the reaction will not produce a color change. The overall experiment can be described by the following series of reactions:<\/p>\n\n\n\n

IO3<\/sub>–<\/sup> + 3 HSO3<\/sub>–<\/sup> –> I–<\/sup> + 3 SO4<\/sub>-2<\/sup> + 3 H+<\/sup><\/p>\n\n\n\n

IO3<\/sub>–<\/sup> = 8 I–<\/sup> + 6 H+<\/sup> –> 3 I3<\/sub>–<\/sup> + 3 H2<\/sub>O<\/p>\n\n\n\n

I3<\/sub>–<\/sup> + HSO3<\/sub>–<\/sup> + H2<\/sub>O –> 3 I–<\/sup> + SO4<\/sub>-2<\/sup> + 3 H+<\/sup><\/p>\n\n\n\n

2 I3<\/sub>–<\/sup> + starch –> starch-I5<\/sub>–<\/sup> complex (blue)The generation in of I3<\/sub>–<\/sup> in the presence of starch generates the blue starch color change. The triiodide ion is consumed by any remaining bisulfite ion, which prevents starch complexation. So the color change occurs when the bisulfite ion is consumed.<\/p>\n\n\n\n

Materials<\/strong><\/h3>\n\n\n\n