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Predominance diagram for chromate. A predominance diagram purports to show the conditions of concentration and pH where a chemical species has the highest concentration in solutions in which there are multiple acid-base equilibria. [1] The lines on a predominance diagram indicate where adjacent species have the same concentration.
The predominance diagram shows that the position of the equilibrium depends on both pH and the analytical concentration of chromium. [ notes 1 ] The chromate ion is the predominant species in alkaline solutions, but dichromate can become the predominant ion in acidic solutions.
The predominance diagram is interpreted as follows. The chromate ion, CrO 2− 4, is the predominant species at high pH. As pH rises the chromate ion becomes ever more predominant, until it is the only species in solutions with pH > 6.75. At pH < pK 1 the hydrogen chromate ion, HCrO − 4 is predominant in dilute solution.
Partial predominance diagram for chromate. Molecular chromic acid, H 2 CrO 4, in principle, resembles sulfuric acid, H 2 SO 4. It would ionize accordingly: H 2 CrO 4 ⇌ [HCrO 4] − + H + The pK a for the equilibrium is not well characterized. Reported values vary between about −0.8 to 1.6. [4]
4 Predominance Diagram. 1 comment. 5 Issue about the opening. ... Talk: Chromate and dichromate. Add languages. Page contents not supported in other languages. Article;
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S&P show the sulfide anion at pH ca. 13. Their wording accompanying the predominance diagram is interesting as they say it shows, "the properties of the major sulfur species [italics added] pertinent to aqueous chemistry" and that, "other species [which they list in a separate table] are thermodynamically unstable with regard to these." p.
Chromate conversion coating, a method for passivating metals; Biology. Monochromacy (monochromate) having one color vision; Dichromatism (dichromate) having two color ...