How to find the Oxidation Number for Cr in the Cr2O7 2- ion. (Dichromate ion)

To find the oxidation number for Cr in Cr2O7 2- (the Dichromate ion), and each element in the ion, we use few simple rules and some simple math.

First, since the Dichromate ion has an overall charge of 2- we could say that the oxidation numbers in Cr2O7 2- need to add up to charge on the ion.

We write the oxidation number (O.N.) for elements that we know and use these to figure out oxidation number for Cr.

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GENERAL RULES
In an ion all Oxidation numbers must add up to to the ion charge.
Group 1 = +1
Group 2 = +2
Hydrogen with Non-Metals = +1
Hydrogen with Metals (or Boron) = -1
Fluorine = -1
Oxygen = -2 (except in H2O2 or with Fluorine)
Group 17(7A) = -1 except with Oxygen and other halogens lower in the group
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We know that Oxygen usually is -2 with a few exceptions. When Oxygen is in a peroxide, like H2O2 (Hydrogen peroxide), it has a charge of -1. When it is bonded to Fluorine (F) it has an oxidation number of +2.

Here it is bonded to Cr so the oxidation number on Oxygen is -2. Using this information we can figure out the oxidation number for the element Cr in Cr2O7 2-.

[rileyomalley]

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[ESLMathTutor]

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[mariaarellano]

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[gunjanpandey]

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Gratitude from India.

[skzonthetop]

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[gaby]

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[danyac]

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[r_playz_wr]

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[davideldredge]

In all my years of chemistry, both in class as a student and teaching the labs, I have yet to see a text book show Cr(VI). I have my students memorize the tabels of transition metals and the various oxidation states. I have only seen Cr(II) & Cr(III), why do these books leave out the most common, Cr(VI) [and the most hazardous], which is still used today by Boeing and their tier 1 suppliers when coating aluminum parts?

[afkdyz]

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[bhumikumawat]

Great sir I have some confusion in it but now it is

[conanobrian]

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