What Is the Contact Process for Preparation of Sulphuric Acid with Reactions and Conditions
Sulphuric Acid is an Acidic chemical compound with the formula H2SO4. It is widely used in the industries that is why it is called the king of chemicals. Its worldwide production clearly indicates its industrial strength. In the year 2004, its world production was about 180 million tonnes. It is also known as the oil of vitriol. It is an odourless, colourless and viscous liquid that is soluble in water. Preparation of sulphuric Acid generally involves highly exothermic processes.
The study of the oil of vitriol began in ancient times. It is believed that Muhammad ibn Zakariya al-Razi was the 1st alchemist of Iran who produced Sulphuric Acid. Then in the 17th century, German-Dutch Chemist Johann Glauber prepared Sulphuric Acid by sulphur with potassium nitrate. In 1736, Doctor Joshua Ward used this method for large-scale production of Sulphuric Acid, although it was an expensive method of production. After this many other methods of production of Sulphuric Acid were also discovered but they were not economically feasible.
Then in 1831, British vinegar merchant Peregrine Phillips patented the contact process, in which Sulphuric Acid is produced by using sulphur dioxide and oleum in presence of vanadium pentoxide as a catalyst. This method is more economically feasible than available all other methods and produces concentrated Sulphuric Acid. It is the current method of producing Sulphuric Acid on a large scale and the high concentration required for industrial processes.
Contact Process for Manufacturing of Sulphuric Acid
Industrially, Sulphuric Acid is produced by the reaction of water with sulphur trioxide, which is made by the chemical combination of sulphur dioxide and oxygen, either by the chamber process or the contact process.
Steps involved in the contact process of manufacturing Sulphuric Acid are listed below–
Preparation of sulphur dioxide
Oxidation of sulphur dioxide to prepare sulphur trioxide
Addition reaction of sulphur trioxide and Sulphuric Acid to give oleum
Dilution of oleum to produce concentrated Sulphuric Acid
Preparation of Sulphur Dioxide – In the 1st step sulphur is oxidised or burned to produce sulphur dioxide. The reaction is given below –
S(s) + O2(g) 🡪 SO2(g)
Oxidation of Sulphur Dioxide to Prepare Sulphur Trioxide – Sulphur dioxide is oxidised to sulphur trioxide in presence of vanadium pentoxide as a catalyst. It is an exothermic reaction that is reversible in nature. the reaction is given below –
2SO2(g) + O2(g) V2O5 🡪 2SO3(g)
Addition Reaction of Sulphur Trioxide and Sulfuric Acid to Give Oleum – Sulphur trioxide is absorbed into ~98% Sulphuric Acid to form oleum which is also known as fuming Sulphuric Acid. It is an additional reaction. The reaction is given below –
SO3(g) + H2SO4(I) 🡪 H2S2O7(I)
Dilution of Oleum to Produce Concentrated Sulfuric Acid – Oleum is diluted with water to form concentrated Sulphuric Acid. The reaction is given below –
H2S2O7(I) + H2O(I) 🡪 2H2SO4(I)
It should be noticed here that we used 1 mole of Sulphuric Acid as a reactant and produced 2 moles of Sulphuric Acid.
It is easy to remember the explanation of the Preparation of Sulfuric Acid with emphasis on the currently used preparation method – the Contact Process. If you are looking for NCERT Solutions of Chemistry Subject log on to the Vedantu website or Download the Vedantu learning app. By doing so you will not only get access to free PDFs of NCERT Solutions of Chemistry but other subjects as well.
FAQs on Preparation of Sulphuric Acid by Contact Process and Key Reactions
1. What is the Contact Process for the preparation of sulphuric acid?
The Contact Process is the modern industrial method used for the large-scale preparation of sulphuric acid (H2SO4). It involves three main steps:
- Step 1: Production of sulphur dioxide: S(s) + O2(g) → SO2(g)
- Step 2: Oxidation of SO2 to SO3 using V2O5 catalyst: 2SO2(g) + O2(g) ⇌ 2SO3(g)
- Step 3: Conversion of SO3 to H2SO4 via oleum formation and dilution
2. How is sulphur dioxide produced in the preparation of sulphuric acid?
Sulphur dioxide (SO2) is produced by burning sulphur or roasting sulphide ores in excess air. The common reactions are:
- Burning sulphur: S(s) + O2(g) → SO2(g)
- Roasting iron pyrites: 4FeS2(s) + 11O2(g) → 2Fe2O3(s) + 8SO2(g)
3. Why is vanadium(V) oxide used in the Contact Process?
Vanadium(V) oxide (V2O5) is used as a catalyst because it increases the rate of oxidation of SO2 to SO3 without being consumed. In the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), V2O5 provides:
- High conversion efficiency at about 450°C
- Lower cost compared to platinum catalyst
- Resistance to poisoning by impurities
4. Why is sulphur trioxide not directly dissolved in water to form sulphuric acid?
Sulphur trioxide (SO3) is not directly dissolved in water because the reaction is highly exothermic and produces a fine mist of sulphuric acid that is difficult to condense. The direct reaction is SO3(g) + H2O(l) → H2SO4(l). Instead:
- SO3 is absorbed in concentrated H2SO4 to form oleum (H2S2O7)
- Oleum is then diluted: H2S2O7(l) + H2O(l) → 2H2SO4(l)
5. What are the main steps in the preparation of sulphuric acid by the Contact Process?
The preparation of sulphuric acid by the Contact Process involves purification, oxidation, and absorption steps. These are:
- Purification of SO2: Removal of dust and impurities
- Catalytic oxidation: 2SO2(g) + O2(g) ⇌ 2SO3(g) (V2O5, 450°C, 1–2 atm)
- Absorption: SO3 absorbed in H2SO4 to form oleum
- Dilution: Oleum diluted to obtain concentrated H2SO4
6. What conditions are required for the oxidation of SO2 to SO3?
The oxidation of SO2 to SO3 requires moderate temperature, slight pressure, and a catalyst for maximum yield. The optimal conditions are:
- Temperature: ~450°C
- Pressure: 1–2 atm
- Catalyst: V2O5
7. What is oleum and how is it formed?
Oleum is disulphuric acid (H2S2O7) formed by dissolving sulphur trioxide in concentrated sulphuric acid. The reaction is:
- SO3(g) + H2SO4(l) → H2S2O7(l)
8. What is the role of purification in the preparation of sulphuric acid?
Purification removes dust, arsenic compounds, and moisture that can poison the catalyst in the Contact Process. The steps include:
- Cooling gases to remove impurities
- Passing through scrubbers and drying towers
- Removing arsenic oxide impurities
9. How do you write the balanced chemical equations for the preparation of sulphuric acid?
The balanced equations for sulphuric acid preparation in the Contact Process are:
- S(s) + O2(g) → SO2(g)
- 2SO2(g) + O2(g) ⇌ 2SO3(g)
- SO3(g) + H2SO4(l) → H2S2O7(l)
- H2S2O7(l) + H2O(l) → 2H2SO4(l)
10. Why is sulphuric acid called the king of chemicals?
Sulphuric acid is called the king of chemicals because its production volume indicates a country’s industrial development. It is widely used in:
- Manufacture of fertilizers (e.g., superphosphate, ammonium sulphate)
- Petroleum refining
- Manufacture of detergents, dyes, and explosives
- Lead-acid batteries
