Question

When zinc reacts with very dilute the oxidation state of Nitrogen changes from:
A. $+5\,to\,+1$
B. $+5\,to\,-3$
C. $+5\,to\,+4$
D. $+5\,to\,+3$

Answer 1

Hint: Usually when a reaction of nitric acid and zinc takes place zinc nitrate is formed. But in case of reaction of zinc with very dilute nitric acid ammonium nitrate is formed as well.

Complete step by step answer:
Normal reaction of zinc with Nitric acid
1. \[Zn+HN{{O}_{3}}\left( dilute \right)\to Zn{{\left( N{{O}_{3}} \right)}_{2}}+{{H}_{2}}O+{{N}_{2}}O\uparrow \]
Reaction of zinc with VERY dilute Nitric Acid

2. \[4Zn\left( s \right)+10HN{{O}_{3}}\to \text{4}Zn{{\left( N{{O}_{3}} \right)}_{2}}+N{{H}_{4}}N{{O}_{3}}+3{{H}_{2}}OCl\]
In the second reaction, we can see that the oxidation of nitrogen in \[HN{{O}_{3}}\] is\[+5\]. Whereas the oxidation state of nitrogen in\[N{{H}_{Y}}N{{O}_{3}}\] (ammonium nitrate) is\[-3\].
Therefore, when zinc reacts with very dilute nitric acid, the oxidation state of nitrogen changes from \[+5\] to \[-3\]
So, the correct answer is “Option B”.

Note: 1. You need to be attentive while reading the question. Read the word "very carefully”, otherwise you'll form only zinc nitrate and may forget ammonium nitrate.
2. Oxidation state refers to the degree of oxidation of an atom in a molecule.
3. Don't get confused between the words ‘oxidation state’ and & ‘Oxidation Number’ as both of them are often used interchangeably.
4. The \[{{N}_{2}}O\] gas is also known as Nitrous oxide (IUPAC - Dinitrogen Monoxide) as colorless sweet – tasting gas. It is also known as "Laughing Gas".
5. When metals react with nitric acid \[\left( HN{{O}_{3}} \right)\]the reaction does not produce hydrogen gas. That happens because as soon as the gas is formed, it will be oxidized to water.
6. At the same time, the acid will be reduced.
7. The more dilute the nitric acid, the greater the reduction.
8. Oxidation state is the charge of an atom if all bonds it formed were ionic bonds.