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Lameck Fimbo

How are chromate ions converted in dichromate ions?

David Sandiford  Follow

By condensation in the presence of acid…?

[math]underbrace{2CrO_{4}^{2-} +2H^{+} longrightarrow Cr_{2}O_{7}^{2-} + H_{2}O(l)}_{ext{orange to red}}[/math]

Note that we both forms feature the [math]Cr(VI+)[/math] oxidation state…

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Dan Martin  Follow

The chromate anion, CrO₄²¯, and the dichromate anion, Cr₂O₇²¯, are related to each other through the following acid-base equilibrium:

2CrO₄²¯(aq) + 2H₃O⁺(aq) ⇆ Cr₂O₇²¯(aq) + 3H₂O(l)

You convert the chromate into bichromate by lowering the pH.

Basically, the more acidic the solution, the more predominant the dichromate anion becomes. Poly condensation products are indeed known for strongly acidic solutions.

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