What is the oxidation state of chromium in the dichromate ion, "Cr"_2"O"_7^(2-)?

Nov 27, 2014

+6

Explanation:

Problem: What is the oxidation number (O.N.) of chromium (Cr) in the dichromate ion ${\text{Cr"_2"O"_7}}^{2 -}$?

Let the O.N. of Cr be $x$. The O.N. of oxygen is -2.

The sum of the oxidation states in an ion must add up to the charge on the ion. The dichromate ion has a charge of ${\text{2}}^{-}$, as indicated by its formula, ${\text{Cr"_2"O"_7}}^{2 -}$.

$2 \cdot x$ + $7 \cdot$(-2) = (-2)

$2 \cdot x$ - 14 = -2

Add 14 to both the sides;

$2 \cdot x$ -14 +14 = -2 +14

$2 \cdot x$ = 12

Divide both sides by 2 ;

$\text{2x"/2}$ =$\text{12"/"2}$

$x = 6$

The oxidation number of chromium in the dichromate ion is $+ 6$.

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