Question

The sum of the oxidation states of the nitrogen atom in hyponitrous acid, nitric acid & nitrous acid is:

Answer 1

The loss or gain of electrons from an atom in due course of a reaction to form a chemical bond is called oxidation state. The trick to answer this question is that the sum of oxidation states of the atoms in an ion is equal to the overall charge on the ion.

Complete step by step answer:
The basic need to answer this question is that you need to know the chemical formula of all the compounds mentioned in the question.
Let’s start with hyponitrous acid. The formula is ${N_2}{\left( {OH} \right)_2}$ . Now we need to calculate the oxidation state of nitrogen atoms here.

Let’s take the oxidation state of nitrogen be $x$
Since, two nitrogen atoms are there hence it will be $2x$
And hydroxyl ion that is $\left( {O{H^ - }} \right)$ carry a charge of $- 1$
Two hydroxyl ion will have a total charge of $- 2$
And we can see that the compound is electrically neutral, that the formal charge on the atom is $0$
So, we can say that $2x$ $+$ $( - 2)$ $=$ $0$
So, solving this we get $x$ as $1$
Similarly, the structure of nitric acid is $HN{O_3}$
Let’s take the oxidation state of nitrogen be $y$
As we know it is an acid, so it can furnish ${H^ + }$ ions
Hence, the hydrogen atom has a charge of $+ 1$
Three oxygen atoms with each of charge $- 2$ has a total charge of $- 6$
And the compound as a whole is electrically neutral
Hence, we can say that
$y$ $+ 1$ $+$ $( - 6)$ $=$ $0$
So, solving this we get $y$ as $+ 5$
Similarly, the structure of nitrous acid is $HN{O_2}$
Let’s take the oxidation state of nitrogen be z$$$${\text{ }}
The hydrogen atom has a charge of $+ 1$
Two oxygen atoms with each of charge $- 2$ has a total charge of $- 4$
And the compound as a whole is electrically neutral
Hence, we can say that
$z$ $+ 1$ $+$ $( - 4)$ $=$ $0$
So, solving this we get $z$ as $+ 3$

So, according to the question the sum of the oxidation states will be $x + y + z$ or $1 + 5 + 3 = 9$.

Note:
You should note here that the oxidation state of Hydrogen ion is taken as $+ 1$. It is only because it is an acid and can furnish ${H^ + }$ ions. In case of bases the charge of Hydrogen can be $- 1$ too & those are known as hydride ions.