Question

Dichromate ion is treated with base, the oxidation number of Cr in the product formed is?

Answer 1

Hint: Oxidation number in a chemical equation represents the number of atoms or ions that have been lost or gained by an atom present in that element. If the oxidation number is positive, it means that the element loses the electrons. If it is negative, it means it gains an electron. A net-zero oxidation number means neither gain nor loss of an electron. The oxidation state of the atom in the homopolar elements is also equal to zero.

Complete Step by Step Solution:
When dichromate ion is treated with base, the oxidation number of Cr can be written as a chemical equation as :
\[C{r_2}O_7^{2 - } + 2O{H^ - } \rightleftharpoons 2CrO_4^{2 - } + {H_2}O\]
For \[CrO_4^{2 - }\]
\[x + ( - 2 \times 4) = - 2\]
\[x = 6\]
Hence, the oxidation number of Cr when dichromate ion is treated with base is +6 .
The oxidation number in a monatomic atom will be equal to its charge.

Note: Oxidation states that are more than three, does not exist. There are certain points about oxidation numbers such as:
1) Oxidation number of all alkalis metal ions is always equal to +1 .
2) Oxidation number of all alkaline earth metal ions is always equal to +2 .
3) Oxidation number of boron family metal ions is equal to +3 .
4) Oxidation number of hydrogen ion in the proton is equal to +1 and in the hydride, the ion is equal to -1.
5) Oxidation number of oxygen in the oxide ion is -2 and in the peroxide, the ion is equal to -1 .