[Janey]

Hello again ,
for the next lesson I have to prepare a presentation on chromium chemistry including the reaction of dichromate with hydrogen peroxide.
My teacher gave the reaction mechanisms to me, therefore all I have to do is arranging the oxidation states:
Cr₂O₇^2- + 4 H₂O₂ + 2 H⁺ ---->  2 CrO₅ + 5 H₂O

To me it looks like disproportionation, but I'm absolutely confused about the states, because chromium remains 6+ and only the oxygen changes
I hope someone is able to help me, otherwise I'm totally lost ^^

Chrome(VI)-peroxide:

[Borek]

Cr(V)O₅ - at least that's what is stated in my inorganic chemistry book.

That's redox, with peroxide working as a reducing agent.

[FeLiXe]

The reaction is not a redox reaction. All the oxidation numbers stay the same. In Perchrome(VI)-oxide four of the oxygens have the oxidation number -I. They are only bonded with one bond to the chromium with the other bond to another oxygen. Therefore they only gain one extra electron.

If you want you could see it just as the formation of a different complex. Oxide is taken away and peroxide added. Besides that dichromate is split up to chromate.

[Janey]

Thanks for helping me =)
My teacher has been ill the previous week therefore I couldn't ask him about that one, but the question concerning this task is 'what is oxidized? What is reduced? Arrange the oxidation states'.
Is it chemically correct to say, that some kind of transposition takes place (I mean if I'd say that in class *g*)?

@FeLiXe
The splitting up of the dichromate is asymmetrical, do you mean that the oxide with the double bond is taken away?  

Besides, does anyone know what happens to the chromate in-between the two chromates in the dichromate?

[Borek]

the question concerning this task is 'what is oxidized? What is reduced? Arrange the oxidation states'.

I have rechecked and it seems I was wrong on this one, Cr in CrO₅ is +6.

Perhaps more later, I am in hurry now