# Question #608d1

Nov 17, 2017

The oxidation number of $C r$ is $+ 6$

#### Explanation:

We will rewrite the formula as an equation.

$2 K + 2 C r + 7 O = 0$

The zero comes from there being no overall charge on the compound.

Each oxidation number is represented by the element's symbol.

Since this compound is not a peroxide or superoxide, the oxidation value for $O$ is $- 2$.

$K$ being in group 1 has a $+ 1$ charge and therefore has an oxidation number of $+ 1$

Now, by putting known values in we have:
$2 \left(+ 1\right) + 2 C r + 7 \left(- 2\right) = 0$

$2 + 2 C r - 14 = 0$

$2 C r = 0 + 14 - 2 = + 12$

$C r = + \frac{12}{2} = + 6$

To make it clear, we must keep the positive sign even if we know it is positive.

Nov 17, 2017

$+ 6$.

#### Explanation:

$\text{K}$ has an oxidation number of $+ 1$. There are two $\text{K}$ atoms, thus $+ 2$ oxidation number for both $\text{K}$.

$\text{O}$ has an oxidation number of $- 2$. There are seven $\text{O}$ atoms, thus $- 14$ oxidation number for all $\text{O}$ atoms.

Overall, the oxidation numbers have to equal 0 as it is an uncharted molecule.

Thus

$- 14 + 2 = - 12$

So the $\text{Cr}$ atoms have to have a combined oxidation number equaling $+ 12$ to cancel out the $- 12$ number we just calculated.

There are $2$ $\text{Cr}$ atoms present, and so

$\frac{+ 12}{2} = + 6$