2019 Year 12 IB Extended Essays

form behind the diffusion front. The remaining silver continues to diffuse towards the nuclei, allowing for a space to exist. This disparity causes the remaining reactant to travel through the newly created space before it can repeat the cycle. As a result, the silver nitrate must diffuse for a greater distance before it is able to be saturated enough to allow or precipitate formation (Smith, 1984). This diffusion reaction should also be present in all formations of rings including cobalt (II) chloride and ammonia. Ostwald’s model of supersaturation has been widely regarded as an adequate explanation for the Liesegang phenomena, on the basis that it can explain the spacing and time laws of the pattering. However, at the same time, Ostwald’s model does not explain revert pattering and other documented anomalies found in the patterning (Büki, 2007). Revert pattering is when the usual spacing laws (which show that “interspacing between successive zones increases with increasing ordinal number”) is opposite. Thus, successive rings decrease with their ordinal numbers. This anomaly is rare, and hard to produce intentionally, yet appears in a system which should follow the rules of regular patterning. S PACING L AWS Even though the chemical process of formations is still disputed, and an exact model has not yet been achieved, several mathematical regularities do appear both in space and time. One of these mathematical regularities is the spacing law first described by Jablczinsky in 1923. Jableczinksy noticed that the ratio of the distance from gel surface between adjacent bands is constant (Büki, 2007). This ratio can be expressed in the following equation: = +1 Where X n is the distance of the n th band from the gel surface and P is the spacing coefficient.

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