Question

What is the sulphuric acid obtained from ferrous sulphate (green vitriol) fumes strongly in moist air, on account of the long-continued practice of the process at Nordhausen called?
A. Fuming sulphuric acid
B. Nordhausen sulphuric acid
C. Vitroling sulphuric acid
D. Both A and B

Answer 1

Hint: It is found that historically the biggest production of Fuming sulphuric acid came from distillation of iron sulphates at Nordhausen, from which the historical name Nordhausen sulphuric acid is derived. The structure of Fuming sulphuric acid is:

Complete Solution :
- Let’s discuss about the preparation of Fuming sulphuric acid:
It is found that Fuming sulphuric acid is prepared by the dry distillation of sulphate of iron. $\left( FeS{{O}_{4}}.7{{H}_{2}}O \right)$ is firstly gently heated in the air till all the water is expelled completely and the part of ferrous sulphate is oxidized to ferric state.
- In the next step the mixture of sulphates is then kept in small iron retorts, which are heated in a fumace. The decomposition takes place in accordance with the following equation:
\[F{{e}_{2}}{{(S{{O}_{4}})}_{3}}.2FeS{{O}_{4}} =
2F{{e}_{2}}{{O}_{3}}+4S{{O}_{3}}+S{{O}_{2}}\]

- Further, we can see that the vapours of sulphuric anhydride and sulphur dioxide are condensed in receivers that contain oil of vitriol, which is found to dissolve them.
- Thus, the Nordhausen acid is formed, which is basically fuming in the air and is brown oily liquid. Finally, by cooling to ${{0}^{\circ }}C$, crystals of pyrosulphuric acid (${{H}_{2}}{{S}_{2}}{{O}_{7}}$) separate.
- Nordhausen acid is chiefly produced in Bohemia, where a petroliferous shale is found that forms a basic sulphate of iron, which is then dried and distilled.
Hence, we can conclude that the correct option is (d) Both A and B are Fuming sulphuric acid and Nordhausen sulphuric acid.
So, the correct answer is “Option A”.

Note: We must note here that fuming sulphuric acid is also called as oleum (${{H}_{2}}{{S}_{2}}{{O}_{7}}$), these terms basically refer to solutions of various compositions of sulphur trioxide in sulphuric acid or we can say sometimes more specifically to disulfuric acid.