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.

Answer 2

The oxidation number is the charge when the bonds are ionic in the atom. The oxidation state of potassium is +1, oxygen is -2 and chromium is +6.

What is the oxidation state?

The oxidation state or the number is the total of the electron gained or lost by the atom to form the chemical bond.

Potassium is always +1, and oxygen is -2 except in some cases.

The state can be shown as:

$\rm K_{2} (+1 \times 2) = +2$

Cr (2x) = 2x

$\rm O_{7} (-2 \times 7) = -14$

When the compound is neutral and the net charge is 0 then,

$\begin{aligned} \rm +2 +2x + (-14) &= 0\\\\\rm 2x -12& = 0\\\\\rm x &= +6\end{aligned}$

Therefore, the oxidation number of chromium is +6.

Learn more about oxidation numbers here:

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