Landolt Iodine Clock Reaction

The Landolt Iodine clock reaction is used to show chemical kinetics and reaction mechanisms as well as the effect concentration has on reaction rates. Mechanisms are a very exact and detailed way of telling what happens to molecules at each level in a reaction. Mechanisms include things such as how the molecular geometry of the reagents change throughout the reaction and tells which bonds are broken/formed. In this reaction, two clear liquids are poured together into a beaker and mixed. It yields a clear liquid. However, after waiting for a few minutes, the clear liquid isn’t clear anymore, but is a dark blue. The “clock” in the title of the experiment really isn’t a clock at all. It just refers to the fact that the time that it takes for the solutions to turn a dark blue depends of the concentrations of the reagents used.(1)

There are many variations of this lab that can be done that all illustrate the idea of chemical kinetics. Hydrogen peroxide can be used, as well as iodate, persulfate, and chlorate. The variation of hydrogen peroxide uses the following reagents: hydrogen peroxide, potassium iodide, hydrochloric acid, starch and thiosulfate. The basic reaction for this variation is as followed: H2O2 + 3 I- + 2 H+ → I3- + 2 H2O. The reactants are hydrogen peroxide, hydrogen ions the ions of hydrogen come from the hydrochloric acid), and iodine ions (the iodine ions come from the potassium iodide). In this equation the reactants of liquid hydrogen peroxide, and the ions of the iodine, and hydrogen acid react together to produce triiodide and water as products.

The second reaction in the experiment is as followed: I3S- + 2 S2O32- → 3 I- + S4O62- . The reactants of triiodate and the thiosulfate ions (from the thiosulfate) r...

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... is not the only thing it taught the community of chemists though, it also showed that reactions are able to sit at equilibrium for a while before fully going to completion. After the academy had seen the work he had done in with the reaction, he became a director of the Second Chemical Institute of the Berlin University. He worked here from 1891 to 1905. During this time he also proved the law of concentration of mass and energy to be true, adding to his contributions the science of chemistry. He died in 1910. (3)

This experiment was ground- breaking for many reasons. First, it displayed a clear end that happens after a an defined amount of time.

Works Cited

1.) http://en.wikipedia.org/wiki/Iodine_clock_reaction

2.) http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p091.shtml#background

3.) http://en.wikipedia.org/wiki/Hans_Heinrich_Landolt