Different metal species may predominate in a given aqueous system depending on its pH and redox potential. To summarize such predominances, Pourbaix devised a graphical representation that facilitates the prediction of the most stable species under a given set of E and pH values, as discussed in Section 2.3. Those reactions involving only electron exchange are ¿s-dependent and when plotted they give horizontal lines, whereas those involving H+ or OH- (but not e~) are pH-dependent and give vertical lines. Equilibrium calculations for reactions involving both (e~ and H+/OH~ exchange) yield inclined lines.

In the present experiment, several chemical and electrochemical transitions—some including the metal itself—can be predicted and verified using simple reagents and in uncomplicated conditions (see Ibanez et al., 2005). Copper was selected because of the different colors of its compounds, its relatively low toxicity, wide availability in fairly pure form, and low cost. Ten different transitions

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