What is the oxidation number of cr in Cr2O7^2-?

1 Answer
Nam D.
Apr 13, 2018

#+6#

Explanation:

This is the dichromate ion, #Cr_2O_7^(2-)#.

Oxygen is more electronegative than chromium, so it'll take its usual #-2# charge here. There are seven oxygen atoms, so the total charge is #-2*7=-14#.

Let #x# be the oxidation number of two chromium atoms. So, we got:

#x+(-14)=-2#

#x-14=-2#

#x=12#

So, two chromium atoms have a total oxidation number of #+12#. Since one is not more electronegative than the other, we can divide the number by two to get one chromium's oxidation number.

#12/2=6#

So, a chromium atom here has an oxidation number of #+6#.

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