Question

In conversion of $SO_2$ to $SO_3$, Which of the following is the required catalyst?
A) $Fe$
B) $Pt$ or $V_2O_5$
C) $Co$
D) $Ni$

Answer 1

Hint: As we know that sulphuric acid is the most important industrial chemical and its preparation usually requires three steps and the process is called contact process. One of the steps is conversion of sulphur dioxide to sulphur trioxide.

Complete answer
As we already know that sulphuric acid is one of the most important industrial chemicals used in laboratories world-wide and its manufacturing process usually called contact process requires three main steps. So let us talk about these steps.

The first step involves the burning of sulphur or sulphide ores in air to generate sulphur dioxide. This sulphur dioxide is purified by removing the impurities such as arsenic compound.

Next step is the conversion of sulphur dioxide into sulphur trioxide, where two molecules of sulphur dioxide are reacted with oxygen inside a lead chamber in the presence of catalyst Vanadium pentoxide at a temperature of ${450^\circ }C$and a pressure of $1atm$.

The reaction can be shown with the help of an equation which is given as:
$2S{O_2} + {O_2}\xrightarrow{{{V_2}{O_5}}}2S{O_3}$
This reaction is highly exothermic and releases an energy of $ - 196.6\;kJmo{l^{ - 1}}$.

In the last step this sulphur trioxide is absorbed in sulphuric acid to produce oleum $({H_2}{S_2}{O_7})$. Finally dilution of oleum with water results in production of sulphuric acid of the desired concentration which is almost $96 - 98\% $pure.

Hence the correct answer is option ‘B’.

Note: This reaction is an exothermic reaction, reversible as well as forward reaction which leads to decrease in volume therefore, low temperature and high pressure are generally favourable conditions to increase the percentage yield. Purification step is necessary so that no catalyst poisoning can take place in the formation of sulphuric acid.