Question
Question: Which of the following is known as anhydride of nitric acid? A) \({N_2}{O_3}\) B) \({N_2}{O_4}\...
Which of the following is known as anhydride of nitric acid?
A) N2O3
B) N2O4
C) N2O5
D) N2O
Solution
An acid anhydride is that chemical compound which when reacted with water forms acid. So, try and put together the reactions of all the options given above with water and see which one forms nitric acid.
Complete-step- by- step answer:
An acid anhydride or just simply anhydride is that non-metallic oxide which when treated with water leads to the formation of an acidic solution.
We should also know the chemical formula of nitric acid. It is HNO3.
We should now begin by writing the reactions of all the 4 compounds given in the options:
N2O3 or dinitrogen trioxide reacts with water to produce nitrous acid.
$${N_2}{O_3} + {H_2}O \to 2HN{O_2}$$
So, we can say that N2O3 is an anhydride of nitrous acid.
N2O4 or dinitrogen tetra-oxide reacts with water to produce both nitric acid and nitrous acid.
N2O4+H2O→HNO2+HNO3
Since, it gives a mixture of both nitrous and nitric acid it cannot be called anhydride of nitric acid.
N2O5 or nitrogen penta-oxide is also known as nitric anhydride because when it reacts with water it leads to the formation of nitric acid.
$${N_2}{O_5} + {H_2}O \to 2HN{O_3}$$
Since, it leads to the formation of nitric acid on reaction with water it is anhydride of nitric acid.
Although we now have our answer but still for a safe side lets see the last option also.
N2O or nitrous oxide is quite less reactive and does not form any acidic solution with water. Infact on heating it breaks down exothermically into N2 and O2.
$${N_2}O\xrightarrow{\Delta }{N_2} + {O_2}$$
So, from the above discussion we now know that N2O5 is the anhydride of nitric acid.
Therefore,the correct option is: C) N2O5 .
Note: In questions like this we often get confused in the naming and formulas of various compounds. We might get confused in nitric acid and nitrous acid formulas. So, always remember that nitric acid is HNO3 and nitrous acid is HNO2.