Sulphuric acid is one of the most important chemical compounds known. It is very commonly used in the laboratory and almost every manufacturing process makes use of this acid directly or indirectly at some stage. Sulphuric acid is prepared industrially by the contact process.
Sulphur dioxide gas is produced either by burning elemental sulphur in air or roasting iron pyrite in excess of air.
Sulphur dioxide produced above is then passed through purifying chambers and sprayed with steam. This process removes dust impurities as well as arsenic compounds present in the gas. This step is important because arsenic compounds poison the catalyst used later on. The moist gases (SO₂ and O₂) are then dried by passing through a drying tower in which concentrated sulphuric acid is being sprayed. Oxygen used in this reaction is obtained by the fractional distillation of air.
The clean and dry gases (SO₂ and O₂) are then passed over vanadium(V) oxide catalyst at 450°C and 2-3 atmospheric pressure through a contact chamber. Although the reaction is reversible yet under these conditions 98% SO₂ gas is converted to SO₃.
Interesting information: Sulphuric acid is called the “king of chemicals” because it is used in almost every industry.
Sulphur trioxide gas formed in the contact chamber is then absorbed into 98% sulphuric acid to give oleum (disulphuric acid).
The oleum is then mixed with an appropriate amount of water to produce sulphuric acid with desired concentration.
📌 19.2 Quick Check (solutions)
| Session | Learning objectives | Activities & resources | Assessment |
|---|---|---|---|
| Day 1 | Importance of H₂SO₄; preparation of SO₂ (burning S / roasting pyrite) | Discuss “king of chemicals”; show equations S+O₂ and 4FeS₂+11O₂; introduce purification needs | Write balanced equations for SO₂ production |
| Day 2 | Purification of SO₂ and O₂; drying with conc. H₂SO₄; catalyst poisoning (arsenic) | Explain washing with steam, drying tower; why arsenic must be removed | Quick check 19.2 Q2; explain poisoning |
| Day 3 | Oxidation step: 2SO₂+O₂⇌2SO₃; conditions (V₂O₅, 450°C, 2-3 atm); 98% conversion | Discuss reversible reaction, yield, role of catalyst; compare with Haber (if revision) | Recite conditions; explain why 2-3 atm is used (not too high) |
| Day 4 | Absorption of SO₃ (oleum formation) and dilution to H₂SO₄ | Explain why SO₃ is not dissolved directly in water (fumes); oleum + water reaction | Write equations: SO₃+H₂SO₄→H₂S₂O₇; H₂S₂O₇+H₂O→2H₂SO₄ |
| Day 5 | Review whole contact process; integrated quiz | Flow chart drawing; solve 10 MCQs; discuss interesting fact (king of chemicals) | MCQ quiz & key analysis |
⏱️ Each session ~40-45 min. Use @everexams.com quiz for instant feedback.
Click on option — correct turns green, wrong turns red. Use submit to see score & key.