2019 Year 12 IB Extended Essays

I NTRODUCTION When we think of a chemical reaction the idea that it is a process that happens till completion is quite prominent. However, the Belousov-Zhabotinsky (BZ) reaction is an example of an oscillation reaction between potassium bromate, cerium (IV) sulphate, and propanedioic acid (Kemsley, 2011). An

oscillation reaction is the reaction of chemical compounds in which their concentration changes periodically. In the case of the BZ reaction, the solution once stirred changes colour

FIGURE 1 (ANON., 2005)

periodically over time, see figure 1. After seeing this chemical oscillation for the first time, I began researching more types of chemical oscillation. Finally, I came across a reaction known as The Liesegang Ring formation. These formations seemed rather simple to create, intriguing to look at, yet extremely complex chemically. Liesegang rings have been explored for centuries since their discovery in 1896 by German chemist and photographer Raphael Eduard Liesegang. After doing a pre-test, see appendix 1, and further research the a question arose for me ,

“What is the effect of reactant concentration in the formation of Liesegang rings in a gel.”

This overarching question was then refined to a specific experiment.

“What is the effect of the mass of cobalt (II) chloride in the distances between Liesegang ring formations of cobalt (II) chloride and ammonia in a gel.”

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