Question

What is the oxidation number for all elements of $AsO_{4}^{3-}$?

Answer 1

Hint: To solve this question, we first need to know what the oxidation number is. In a chemical compound, the degree of oxidation of an atom can be determined using its oxidation number or the oxidation state.

Complete answer:
First, let us look at the rules to determine the oxidation number of an element.
1. For a free element, the oxidation number of an element in a is always 0.
For example, in helium and nitrogen, the oxidation number of the He and N molecule will be 0.
Similarly, the sum of all the atom's oxidation numbers of a compound that is neutral is 0.
2. The oxidation number of an ion, whether it is monatomic or polyatomic, is equal to the charge on the in.
For example, the oxidation number of $M{{g}^{2+}}$ is +2. The oxidation number of phosphate ions $P{{O}_{4}}^{3-}$ is -3.
3. The usual oxidation number of
Hydrogen = +1
Oxygen = -2
Group I(A) = +1
Group II(A) = +2
Group VII(A) = -1
Now let us determine the oxidation number for all elements of $AsO_{4}^{3-}$.
The usual oxidation state of the oxygen atom is -2.
So, according to the rules, we can say that
\[\begin{align}
  & As+[4\times (-2)]=-3 \\
 & As=+5 \\
\end{align}\]
So, the oxidation number of As is +5 and that of O is -2.

Note:
It should be noted that there are some exceptions while assigning the oxidation states of atoms in a molecule.
- When a hydrogen atom is bonded to a less electronegative atom, its oxidation number is -1.
- When an oxygen atom is bonded to a more electronegative atom, it exists in a peroxide ion, its oxidation number changes.
- When a Group VII(A) atom is bonded to a more electronegative atom, its oxidation number changes.