Phase 1 Products Conceptualization chapter

Through this chapter we would like to express our appreciation of all these educational concepts. Besides (not in contrast) the conceptions mentioned above, our intention is to initialise a process of reflection and maybe of conceptual change for the learners. Learning about the history of science into more detail can be a desired by-product , but it is not the main focus of the approach described above. Therefore, it is our aim to promote learning about basic processes in chemical enquiry, whereas the other projects mainly focused on learning about single topic or phase in the history of chemistry. 

Sol id Sol utions. The aqueous concentrations of trace elements in natural waters are frequently much lower than would be expected on the basis of equilibrium solubility calculations or of supply to the water from various sources. It is often assumed that adsorption of the element on mineral surfaces is the cause for the depleted aqueous concentration of the trace element (97). However, Sposito (Chapter 11) shows that the methods commonly used to distinguish between solubility or adsorption controls are conceptually flawed. One of the important problems illustrated in Chapter 11 is the evaluation of the state of saturation of natural waters with respect to solid phases. Generally, the conclusion that a trace element is undersaturated is based on a comparison of ion activity products with known pure solid phases that contain the trace element. If a solid phase is pure, then its activity is equal to one by thermodynamic convention. However, when a trace cation is coprecipitated with another cation, the activity of the solid phase end member containing the trace cation in the coprecipitate wil 1 be less than one. If the aqueous phase is at equil ibrium with the coprecipitate, then the ion activity product wi 1 1 be 1 ess than the sol ubi 1 ity constant of the pure sol id phase containing the trace element. This condition could then lead to the conclusion that a natural water was undersaturated with respect to the pure solid phase and that the aqueous concentration of the trace cation was controlled by adsorption on mineral surfaces. While this might be true, Sposito points out that the ion activity product comparison with the solubility product does not provide any conclusive evidence as to whether an adsorption or coprecipitation process controls the aqueous concentration. 

Phase 1, which is strategy building, sets the direction, providing a vision for the future and a structure for implementation. The process for Phase 1 will have similar deliverables, tailored to the situation, for each sphere under examination. Chapter 12 describes these tasks in some detail. The end product of Phase 1 is a "conceptual" design. The conceptual design is essentially a justification document. It is in sufficient detail to understand what will be implemented and the costs and benefits of implementation. This will vary from organization to organization. 

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