Question

Explain in detail the manufacture of sulfuric acid by contact process.

Answer 1

Hint:Sulfuric acid is synthesized from gaseous oxides of sulfur. The oxides are sulfur dioxide and sulfur trioxide intermediate formed during the synthesis of sulfuric acid.

Complete step by step answer:
Sulfuric acid is a very strong diprotic acid or a strong mineral acid. The chemical formula of sulfuric acid is \[{H_2}S{O_4}\] . It absorbs water so it acts as a dehydrating agent or an oxidizing agent. The acid appears as a colourless liquid. It is soluble in water and generates heat on dissolution.
 The oxidizing nature is observed as the acid is corrosive with metals, wood, tissues and other organic materials. It is extremely hazardous and its exposure causes adverse health effects.
The contact process is based on three steps. The first step involves formation of sulfur dioxide gas. In the second step the sulfur dioxide is converted into sulfur trioxide and in the final step the sulfur trioxide is converted into sulfuric acid. Let us understand the three steps of the contact process in detail.
Step \[1\]. The solid sulfur, \[S\left( s \right)\], is burned by the presence of oxygen in excess air to produce the first intermediate sulfur dioxide gas,\[S{O_2}\left( g \right)\] . The reaction is
$S(s) + {O_2}(g) \to S{O_2}(g)$
Step \[2\]. The sulfur dioxide gas is treated with oxygen gas of air at \[400 - 450^\circ C\] and a pressure of \[1 - 2atm\]. The reaction is carried out in the presence of a vanadium catalyst (\[{V_2}{O_5}\]​). The starting material gases combine in \[1:1\] ratio to generate sulfur trioxide, \[S{O_3}\left( g \right)\] . The reaction is
$2S{O_2}(g) + {O_2}(g) \to 2S{O_3}(g)$
Step \[3\]. The sulfur trioxide is not dissolved in water as it produces fog. Rather the sulfur trioxide gas is dissolved in 98% sulfuric acid, to produce pyrosulfuric acid or oleum, \[{H_2}{S_2}{O_7}\]​.
${H_2}S{O_4}(l) + S{O_3}(g) \to {H_2}{S_2}{O_7}(l)$
The oleum is then dissolved in water and produces sulfuric acid, \[{H_2}S{O_4}\].
${H_2}{S_2}{O_7}(l) + {H_2}O(l) \to 2{H_2}S{O_4}(l)$

Note:
The unreacted gases obtained after step \[2\] and step \[3\] are from recycled back into the above reservoirs. The process involves oxidation of sulfur and its intermediates.