Question

What is the oxidation state of each element in k2cr2o7?

Answer 1

To begin this, you'll first note down the valencies of atoms you're sure about.

K is always 1+
And O is always 2-, except for in peroxide where it is 1-.

So now you must remember that a compound is always neutral. Your net charge has to be 0.

K2Cr2O7.

K2 (1+ x 2) = 2+
Cr (2x) = 2x
O7 (2- ×7) = 14-

+2 +2x + (-14) = 0
•Simple algebra.
2x -12 = 0
2x = 12
x = +6.

Each Cr atom has an oxidation number of +6.