Question

The process which takes place in absorption tower is:
A. catalytic oxidation of ${\text{S}}{{\text{O}}_2}$ to ${\text{S}}{{\text{O}}_3}$.
B. production of sulfur dioxide by burning sulfur.
C. absorption of sulfur trioxide in $98\%$ sulfuric acid
D. none of the above

Answer 1

Sulfuric acid is one of the most important compounds made by the chemical industry. There are two types of manufacturing processes-contact process and lead chamber process. Sulfuric acid is prepared by the contact process.

Complete step by step answer:
Sulfuric acid is a commercially important raw material. It is prepared from sulfur, air and water. It has many uses. Some of them are:
-Manufacture of plastic items.
-Manufacture of paints
-Manufacture of pesticides and fertilizers
-Manufacture of soaps and detergents
-Manufacture of electrolytes
The contact process involves four stages. Stage $1$ occurs in the furnace, stage $2$ occurs in the convertor and stage $3$ occurs in the absorber. This is also known as absorption tower.
In the furnace, molten sulfur is burnt in dry air to produce ${\text{S}}{{\text{O}}_2}$ which is then purified and cooled.
${\text{S + }}{{\text{O}}_2} \to {\text{S}}{{\text{O}}_2}$
In the convertor, ${\text{S}}{{\text{O}}_2}$ and excess ${{\text{O}}_2}$ gas are passed over few plates of ${{\text{V}}_2}{{\text{O}}_5}$ to produce ${\text{S}}{{\text{O}}_3}$.
$2{\text{S}}{{\text{O}}_2} + {{\text{O}}_2} \to 2{\text{S}}{{\text{O}}_3}$
This is highly exothermic.
In the absorber, ${\text{S}}{{\text{O}}_3}$ is first reacted with ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$ to form oleum, ${{\text{H}}_2}{{\text{S}}_2}{{\text{O}}_7}$
${\text{S}}{{\text{O}}_3} + {{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {{\text{H}}_2}{{\text{S}}_2}{{\text{O}}_7}$
This is then diluted with water to produce ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$ in large quantities.
${{\text{H}}_2}{{\text{S}}_2}{{\text{O}}_7}{\text{ + }}{{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_4}$
The process depends upon three factors-catalyst ${{\text{V}}_2}{{\text{O}}_5}$, temperature ${450^ \circ }{\text{C}}$ and pressure $1 - 2{\text{atm}}$.
Thus in absorption tower, oleum, ${{\text{H}}_2}{{\text{S}}_2}{{\text{O}}_7}$ is formed.

Hence the correct option is D.

Note:
The two reactions in the third stage are equivalent to adding sulfur trioxide directly to water. The reaction is given below:
${\text{S}}{{\text{O}}_{3\left( {\text{g}} \right)}} + {{\text{H}}_2}{{\text{O}}_{\left( {\text{l}} \right)}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_{4\left( {\text{l}} \right)}}$
But this is not done in the industry because ${\text{S}}{{\text{O}}_3}$ reacts violently with water. This produces a lot of heat and a large cloud of ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$ mist which might me corrosive and pollutes the air and is difficult to condense.