Colour of Fe3+

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Homework Statement

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Relevant Equations

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I've been tasked with writing an equation to show the reaction of the Fe2+ complex with Cl2. I believe that the oxidation state of the Iron has changed, so I would write 2Fe(H2O)(6)^2+ + Cl2 -> 2Cl- + 2Fe(H20)(6)^3+, but I can't be sure this is correct.

Is the 2Fe(H20)(6)^3 ion not yellow in water due to the formation of its conjugate base? If so, is there any hint in the question as to why it should appear brown? THANK YOU!!

 

[Borek]

2Fe(H2O)(6)^2+ + Cl2 -> 2Cl- + 2Fe(H20)(6)^3+

General idea is OK, whether some H₂O molecules are not replaced with Cl^-, producing a bit different complex, is another question.

Is the 2Fe(H20)(6)^3 ion not yellow in water due to the formation of its conjugate base?

It is yellowish/brown even in low pH solutions, where the conjugate base is not present.

 

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It's just strange because my textbook (from which this exam question is based off) claims that hydrated Fe3+ is yellow, and all other exam questions on this topic use that piece of information, its just this one that says its brown.

 

[Borek]

Difference between yellow and brown is mostly just intensity, these are not completely different colors. Especially when you take into account that these names of colors are very handwavy, there is no rigor behind. The only way to treat these things seriously is to talk not about "colors" but about spectra.

 

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The joys of chemistry.