2019 Year 12 IB Extended Essays

As the spacing law states that the ratio between a band and its adjacent band is constant, this should be equivalent to the gradient of each trend line. Table 6 shows that this constant ratio is held through each variation. Each trend line has a gradient of 1.2 ± 0.1. This gradient is a reflection of the spacing law. Even with 4.5 grams, which does not follow other expected trends, the spacing coefficient is 1. As established through the qualitative and quantitative data, there is loss of increasing trend between the formation of rings within the 4.0g and 4.5g of cobalt (II) chloride. As demonstrated by the above data, the solution yielding 4.0 grams of cobalt (II) chloride formed 25 rings and displayed an overall precipitate zone of 49 mm. While at 4.5 grams of cobalt (II) chloride in the solution, only 20 rings were formed and displayed a precipitate zone only 35 mm tall. As explained throughout the background research, Ostwald’s model of supersaturation can be used to explain the Liesegang phenomena. The formations manifested within this experiment accurately model Ostwald’s spacing laws (Büki, 2007). As previously noted within Ostwald’s model, it is suggested that the spacing between rings is due to the diffusion of a reactant (in this case cobalt (II) chloride) decreasing in concentration through each ring formation. In this experiment the only increase was of cobalt (II) chloride. This means that for each test the same amount of ammonia was added to the gel. Only the precipitate develops due to the reaction of ammonia and cobalt. The increase of cobalt doesn’t necessarily increase the amount of precipitate formed, as the ammonia is the limiting reagent within the reaction. At some stage there will be insufficient ammonia to react with the cobalt to create another ring. This is shown in the 4.0 and 4.5 formations. Even though there is an extra 0.5grams of cobalt there are less ring formations and the precipitate zone is smaller. Another observation made was the large dissimilarity in the test results and the experiment results. As seen in Appendix 1.1 the test formations (from left to right 2.5g, 3.0g and 3.5g) have

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