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 Sulfuric Acid
1. What is the Contact Process for the industrial preparation of sulfuric acid?
The Contact Process is the modern, highly efficient industrial method used to produce concentrated sulfuric acid. The process involves three main stages:
- Production of Sulfur Dioxide: Sulfur or sulfide ores are burned in the presence of air to produce sulfur dioxide (SO₂).
- Catalytic Oxidation: The sulfur dioxide is then catalytically oxidised with atmospheric oxygen to form sulfur trioxide (SO₃) using Vanadium pentoxide (V₂O₅) as a catalyst.
- Absorption and Dilution: The sulfur trioxide is absorbed into concentrated sulfuric acid to form oleum (H₂S₂O₇), which is then diluted with water to achieve the desired concentration of sulfuric acid.
2. What are the key chemical reactions and their equations in the Contact Process?
The preparation of sulfuric acid via the Contact Process involves a series of critical chemical reactions:
- Step 1: Burning of sulfur to form sulfur dioxide:
S(s) + O₂(g) → SO₂(g) - Step 2: Catalytic oxidation of sulfur dioxide to sulfur trioxide. This is a reversible and exothermic reaction:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) (Catalyst: V₂O₅) - Step 3: Absorption of sulfur trioxide in concentrated H₂SO₄ to form oleum:
SO₃(g) + H₂SO₄(l) → H₂S₂O₇(l) (Oleum) - Step 4: Dilution of oleum with water to produce sulfuric acid:
H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(aq)
3. In the Contact Process, why is sulfur trioxide (SO₃) absorbed in concentrated H₂SO₄ instead of directly in water?
This is a crucial step for process safety and efficiency. The reaction between sulfur trioxide and water is extremely exothermic and violent. If SO₃ were added directly to water, it would produce a fine, highly corrosive mist of sulfuric acid droplets that is very difficult to condense and handle. By absorbing SO₃ into concentrated sulfuric acid, a more manageable product called oleum (H₂S₂O₇) is formed smoothly. This oleum can then be safely and controllably diluted with water to produce sulfuric acid of the required concentration.
4. What is the role of the catalyst and the specific conditions required for the oxidation of SO₂ to SO₃?
The catalyst used is Vanadium pentoxide (V₂O₅). Its role is to increase the rate of reaction by providing an alternative pathway with lower activation energy for the oxidation of SO₂ to SO₃. The efficiency of this step depends on specific conditions based on Le Chatelier's principle:
- Temperature: An optimum temperature of approximately 720 K (450 °C) is maintained. Although lower temperatures favour the forward exothermic reaction, the rate becomes too slow. This temperature is a compromise for a good reaction rate and a high yield.
- Pressure: A relatively low pressure of about 2 bar is sufficient. High pressure favours the forward reaction (as it proceeds with a decrease in gaseous moles), but the yield is already very high (around 96-97%) at this pressure, so expensive high-pressure equipment is not necessary.
5. Why must concentrated sulfuric acid always be added to water slowly, and not water to acid?
The dilution of concentrated sulfuric acid is a highly exothermic process, meaning it releases a significant amount of heat. If you add water to acid, the heat is generated in a small volume of water, which can instantly boil and splash the highly corrosive acid out of the container. To prevent this dangerous situation, you must always add the acid slowly to a large volume of water with constant stirring. This allows the large mass of water to absorb the heat safely and dissipate it gradually.
6. What are the most important physical and chemical properties of sulfuric acid?
Sulfuric acid has several distinct properties:
- Physical Properties: It is a colourless, dense, and oily liquid. It has a high boiling point (611 K) due to strong hydrogen bonding. It is also highly corrosive.
- Chemical Properties: It is a strong dibasic acid that ionises in two steps. It is a powerful dehydrating agent, capable of removing water from other compounds. It also acts as a strong oxidizing agent, especially when concentrated and hot.
7. What are the major uses of sulfuric acid in various industries?
Sulfuric acid is known as the 'King of Chemicals' due to its extensive applications. Its major uses include:
- In the manufacture of fertilisers, such as ammonium sulfate and superphosphate of lime.
- In the chemical industry for producing detergents, pigments, dyes, and other acids like hydrochloric acid.
- In petroleum refining to wash impurities from gasoline.
- As an electrolyte in lead-acid storage batteries used in vehicles.
- In metallurgy for cleaning and pickling of metals before plating.
- As a dehydrating agent and catalyst in many organic reactions.
8. How does the Contact Process differ from the older Lead-Chamber Process?
The Contact Process has largely replaced the Lead-Chamber Process due to its superior efficiency and product quality. The key differences are:
- Catalyst: The Contact Process uses a solid catalyst, Vanadium pentoxide (V₂O₅), while the Lead-Chamber process used gaseous nitrogen oxides (NO).
- Purity and Concentration: The Contact Process produces highly pure and concentrated sulfuric acid (96-98%). The Lead-Chamber process yielded a less pure acid with a lower concentration (around 62-78%).
- Efficiency: The Contact Process is more efficient and has better mechanisms for recycling catalysts and managing pollutants, making it more environmentally and economically viable for modern industrial needs.
