 
       
      
    7.21     Describe the manufacture of  by contact process?
 
                
                  Sulphuric acid is manufactured by the contact process, which involves three steps:
(i) burning of sulphide ores or sulphur in the air to generate.
(ii) conversion of to 
 by the reaction with oxygen in the presence of a catalyst (
 ), and
(iii) absorption of in 
to give Oleum (
)
Diluting the oleum with water gives  of the desired concentration.
 
                 
                