chapter 7.  ELEMENTS OF GROUPS 16, 17 AND 18 class 12 chemistry textbook solution

4. Answer the following.

iv. Describe the manufacturing of H2SO4 by contact process


The Contact Process is a widely used industrial method for the manufacture of sulfuric acid (H2SO4). It involves a series of chemical reactions that convert sulfur dioxide (SO2) into sulfur trioxide (SO3), which is then used to produce concentrated sulfuric acid. Here is an overview of the manufacturing process:

Step 1: Sulfur Combustion and Formation of Sulfur Dioxide (SO2):

  • The process begins with the combustion of elemental sulfur (S) in the presence of air (oxygen). This combustion reaction produces sulfur dioxide gas (SO2).
  • The chemical equation for this step is: S + O2 → SO2

Step 2: Conversion of SO2 to SO3 (Catalytic Oxidation):

  • The sulfur dioxide gas produced in the first step is then converted into sulfur trioxide (SO3) through a catalytic oxidation reaction.
  • The reaction requires a catalyst, which is typically a vanadium(V) oxide (V2O5) or a platinum (Pt) catalyst supported on a substrate.
  • The chemical equation for this step is: 2SO2 + O2 ⇌ 2SO3

Step 3: Absorption of SO3 in Oleum (H2S2O7):

  • The sulfur trioxide gas produced in step 2 is highly reactive and is rapidly absorbed into concentrated sulfuric acid (H2SO4) to form oleum, also known as fuming sulfuric acid (H2S2O7).
  • The chemical equation for this step is: SO3 + H2SO4 → H2S2O7

Step 4: Dilution and Formation of Concentrated Sulfuric Acid (H2SO4):

  • The oleum produced in step 3 is diluted with water (H2O) to form concentrated sulfuric acid (H2SO4).
  • The dilution of oleum with water is typically done in stages to control the reaction temperature and prevent overheating.
  • The chemical equation for this step is: H2S2O7 + H2O → 2H2SO4

Step 5: Optional Formation of Fuming Sulfuric Acid (Oleum):

  • In some cases, oleum (H2S2O7) can be recovered from the process and used for various applications. Oleum has a higher sulfur trioxide content than concentrated sulfuric acid.

The Contact Process is highly efficient and allows for the continuous production of concentrated sulfuric acid. The use of a catalyst and the recycling of sulfur trioxide help optimize the conversion of sulfur dioxide into sulfuric acid. Concentrated sulfuric acid produced through this process finds applications in various industries, including chemical manufacturing, petroleum refining, and as a laboratory reagent.

chapter 7.  ELEMENTS OF GROUPS 16, 17 AND 18 Textbook Solution page 164