Question

Which of the following catalysts is used in the contact process for manufacture of ${H_2}S{O_4}$?
(A) Oxides of nitrogen
(B) ${V_2}{O_5}$
(C) $F{e_2}{O_3}$
(D) Platinized asbestos

Answer 1

Contact process is an industrial process for the production of sulfuric acid (${H_2}S{O_4}$) at a commercial scale. In this process sulfur trioxide, which is in turn converted into sulfuric acid.

Complete step by step answer:
There are various methods employed for the manufacture of sulfuric acid. The most commonly used method is the contact process.
The process is completed in various steps as discussed below:
(i) The sulfur is extracted. Generally during the refining of natural gas, sulfur is recovered from it. Sulfur can also be extracted from metal ores by refining.

(ii) The sulfur is then converted into sulfur and kept in a hot furnace at ${445^\circ }C$. The reaction can be shown as:
$S\left( s \right)\xrightarrow[{{{445}^\circ }C}]{\Delta }S\left( G \right)$
$S\left( g \right) + {O_2} \to S{O_2}\left( g \right)$
Sulfur ore can either be roasted to obtain sulfur dioxide as follows:
$PbS + 3{O_2} \to 2PbO + 2S{O_2}$

(iii) Next step is to convert sulfur dioxide into sulfur trioxide, sulfur dioxide is combined with oxygen in $1:1$ ratio at $400 - {450^\circ }C$
The catalyst employed is vanadium pentoxide (${V_2}{O_5}$).

(iv) This is the last step in which sulfur trioxide is finally converted into sulfuric acid (${H_2}S{O_4}$)
In this step, Oleum is first produced by mixing sulfur trioxide in sulfuric acid. Then, the oleum is dissolved in water to yield sulfuric acid. This can be shown as:
$S{O_3} + {H_2}S{O_4} \to \mathop {{H_2}{S_2}{O_7}}\limits_{({\text{oleum)}}}$
${H_2}{S_2}{O_7} + {H_2}O \to \mathop {2{H_2}S{O_4}}\limits_{({\text{Sulfuric acid)}}}$
As we discussed in the step iii), the catalyst used in the contact process is Vanadium pentoxide (${V_2}{O_5}$). It increases the rate of reaction and thus speeds up the production of sulfuric acid.
Hence, the correct option is B i.e ${V_2}{O_5}$.

Note:
The sulfur trioxide is never directly dissolved in water because it is an exothermic reaction and can cause fuming of ${H_2}S{O_4}$. That is why first oleum is produced and then it is dissolved in water to produce sulfuric acid.