Question

What mass of $ \;HN{O_3} $ ​ is required to make $ 1{{ }}litre $ of $ 2N $ solution to be used as an oxidizing agent in the reaction?
 $ 3Cu + 8HN{O_3}\, \to 3Cu{(N{O_3})_2}\, + 2NO + 4{H_2}O $
(A) $ 63g $
(B) $ 21g $
(C) $ 42g $
(D) $ 84g $

Answer 1

Hint: The chemical name of $ \;HN{O_3} $ is Nitric acid. It is a strong mineral acid that is also known as spirit of niter and aqua forts. It is highly corrosive and toxic in nature. If it comes in contact with skin, it can cause severe burns on it.

Complete Step-by-step Solution:
The reaction of Copper with nitric acid is an example of redox reaction. A redox reaction is given as a chemical reaction which is governed via a transfer of electrons between two atoms or molecules participating in the reaction. This transfer of electrons is observed by calculating the changes that occur in the oxidation states of the reacting species.
In Redox reactions both oxidation and reduction take place in the same reaction. In this type of chemical reaction, one species is oxidised and the other is reduced.
The molecule in which the addition of electrons takes place gets reduced, and the other from which the removal of electrons takes place gets oxidized.
Now, the given reaction is;
 $ 3Cu + 8HN{O_3}\, \to 3Cu{(N{O_3})_2}\, + 2NO + 4{H_2}O $
 $ + 5\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, + 5\,\,\,\,\,\,\,\, + 2 $
In this reaction, the oxidation state of nitrogen changes from $ + 5 $ to $ + 2 $ , and the oxidation state of copper changes from $ 0 $ to $ + 2 $ . Hence the species, whose oxidation state decreases is said to be reduced, and whose oxidation state increase is said to be oxidised.
Now, we will calculate the mass of $ \;HN{O_3} $ ​ that is required to make $ 1{\text{ }}litre $ of $ 2N $ solution. The change in oxidation of $ N $ is $ 3 $ . Hence the equivalent weight of $ \;HN{O_3} $ will be
 $ Equivalent{{ }}weight{{ = }}\dfrac{{63}}{3} = 21g $
Hence, for making $ 1N $ solution we need $ 21g\, $ of $ \;HN{O_3} $
And for making $ 2N $ we will need $ 2 \times 21 = 42g $ of $ \;HN{O_3} $ .
Therefore, option (C) is correct.

Note:
Oxidation numbers represent the potential charge present on an atom in its ionic form. If the atom's oxidation is decreased in a reaction, then it is said to get reduced. If it increases, then the atom is said to get oxidized