Question

What is used as a catalyst in the manufacture of sulphuric acid by the contact process?
A) \[A{{l}_{2}}{{O}_{3}}\]
B) \[{{K}_{2}}O\]
C) \[{{V}_{2}}{{O}_{5}}\]
D) \[Fe\]

Answer 1

Hint: The contact process is used for the preparation of sulphuric acid in high concentrations needed for industrial processes. It consists of a series of steps and the catalyst used is of a transition metal.

Complete answer:
The contact process has the following steps-
The first steps lead to the formation of sulphur dioxide.
\[S(s)+{{O}_{2}}\to S{{O}_{2(g)}}\]
Then the Sulphur dioxide is converted into Sulphur trioxide,
$2SO_2(g) + O_2(g) \xrightarrow{V_2O_5} 2SO_3(g)$
The last step converts the Sulphur trioxide into concentrated sulphuric acid.
$S{{O}_3{(g)}}+{{H}_{2}}S{{O}_{4(aq)}}\to {{H}_{2}}{{S}_{2}}{{O}_{7}}$
${{H}_{2}}{{S}_{2}}{{O}_{7}}+{{H}_{2}}{{O}}\to 2{{H}_{2}}S{{O}_{4(aq)}}$
Vanadium pentoxide is used as the catalyst for the contact process. Its molecular formula is \[{{V}_{2}}{{O}_{5}}\]. It is used in the second step of the process where Sulphur dioxide is converted to Sulphur trioxide. \[{{V}_{2}}{{O}_{5}}\] has no effect on the position of the equilibrium. It speeds up the process. In the absence of \[{{V}_{2}}{{O}_{5}}\] the reaction is so slow that virtually no reaction happens in any sensible time. Vanadium pentoxide along with increasing the rate of the reaction also lowers the temperature and the reaction is able to proceed at the preferred temperature.

Note: In the industrial process for the manufacture of sulphuric acid platinum used to be the catalyst for this reaction. However, as it is susceptible to reacting with arsenic impurities in the sulphur feedstock, vanadium oxide or vanadium pentoxide (as it is commonly known) is new preferred.