Sulphuric Acid H2SO4 – Properties, Reactions & More

Sulphuric Acid H2SO4

Sulfuric acid or sulphuric acid also referred to as oil of vitriol, is a mineral acid made up of the elements sulphur, oxygen and hydrogen, with molecular formula H₂SO₄.

Sulphuric acid was first prepared by a Muslim scientist Jabir bin Hayyan in the 8th century. In Europe, in the 14th and 15th centuries, its preparation on the business level was begun due to the awareness of its properties and usages.

Small quantities of H2SO4 are found in the waters of some springs and rivers.

Manufacture of Sulphuric Acid

Sulphuric acid is being manufactured frequently by the contact process.

Contact Process

This approach was developed by Knietsch in Germany. Basically, it includes the catalytic mix of sulphur and oxygen to form SO2 which is then dissolved in water to form H2SO4.


SO2 acquired by burning sulphur or iron pyrites is oxidized to SO3 in the presence of V2O5 which functions as a catalyst. The very best yield of SO3can be acquired by using an excess of oxygen or air and keeping the temperature in between 400-500 ° C. SO3 formed is absorbed in concentrated H2SO4and “Oleum” (H2S2O7) formed can be converted to sulphuric acid of any strength by mixing sufficient amounts of water.

The process is completed in the series provided listed below.

a.Sulphur Burners

Sulphur or iron pyrites are burnt in excess of air to produce SO2.


b.Purifying Unit

SO2 is cleansed from impurities like dust and arsenic oxide, to avoid poisoning of the catalyst. The cleansing system consists of the following parts.

(i) Dust cleaner

Steam is injected to get rid of dust particles from the gases.

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(ii) Cooling Pipes

The gases are passed through lead pipes to cool them to 100 ° C.

(iii) Scrubbers

The cooled gases are washed by a spray of water, as SO2 is not soluble in water at high temperature.

(iv) Drying Tower

The moisture of gases is gotten rid of by concentratedH2SO4 trickling down through the coke filled in this tower.

(v) Arsenic Purifier

Arsenic oxide is then eliminated by passing the gases through a chamber provided with racks loaded with freshly prepared ferric hydroxide.

(vi) Testing box

In this box, a beam of light is introduced which indicates the presence or absence of solid particles. If present the gases are sent back for further purification filtration.

c.Contact Tower

Preheated gases at 400-500 ° C are passed through vertical iron columns packed with the catalyst V2O5. Here SO2 is oxidized to SO3.


The reaction is extremely exothermic so no heating is needed once the reaction is started.

d.Absorption Unit

The SO3 acquired from the contact tower is dissolved in 98% H2SO4 to form pyrosulphuric acid (oleum), H2S2O7. It can be diluted with water to get any required concentration of sulphuric acid.



Properties of Sulphuric Acid

Physical Properties

  1. Pure sulphuric acid is a colourless oily liquid without a smell.
  2. Its specific gravity is 1.834 at 18 ° C.
  3. It freezes at 10.5 ° C.
  4. Its boiling point is 338 ° C.
  5. It dissolves in water liberating a lot of heat which raises the temperature of the mixture as much as 120 ° C. H2SO4 should always be poured in water in a thin stream to avoid any mishap.
  6. Pure acid is a nonconductor of electricity but the addition of a little water makes it a great conductor.
  7. It is incredibly corrosive to skin and causes really severe burns to all the tissues.

It is stable at ordinary temperature level but on strong heating, it dissociates into SO3 and H2O.


It is a strong acid. In an aqueous solution, it entirely ionizes to give hydrogen, hydrogen sulphate and sulphate ions. The dissociation takes place in two steps.

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Sulphuric Acid as an Acid

(i) Reactions with alkalies


(ii) Reactions with carbonates and hydrogen carbonates


(iii) Reactions with salts


(iv) Reactions with metals

  • Cold dilute acid reacts with almost all metals to produce hydrogen gas and sulphate salts.


  • Cold concentratedH2SO4does do not react with most of the metals like Cu, Ag, Hg, Pb, Au.


  • With specific metals hot concentrated sulphuric acid provides metal sulphates, water and SO2.


Sulphuric Acid as a Dehydrating Agent

H2SO4 has a great affinity for water, so it acts as a dehydrating agent and removes water from different compounds.

For instance:

  • With formic acid, CO is formed.



  • With ethyl alcohol, it forms ethylene.


  • With wood, paper, sugar and starch it forms carbon and water.


Sulphuric Acid as an Oxidizing Agent

H2SO4 acts as a strong oxidizing agent.

It oxidizes C and S giving CO2 and SO2, respectively.


H2S is oxidized to S.


Reactions of H2SO4with HBr and HI produces bromine and iodine respectively.


Uses of Sulphuric Acid

It is used

  1. in the manufacture of fertilizers like ammonium sulphate and calcium superphosphate.
  2. in the refining of petroleum to get rid of nitrogen and sulphur substances.
  3. in the manufacture of HCl, H3PO4, HNO3 and sulphates.
  4. in the manufacture of numerous chemicals, dyes, drugs, plastics, disinfectants, paints, explosives, artificial fibres, etc.
  5. in electrical batteries and storage cells.
  6. as a dehydrating agent for drying gases.
  7. as a laboratory reagent.
  8. in textile, iron, steel, leather and paper markets.
Frequently Asked Questions

Q1: Why sulphuric acid is called oil of vitriol?

Ans: Sulphuric acid is a very strong, corrosive mineral acid. Its typical name oil of vitriol shows the virulency of acid.

Q2: What is the natural occurrence of sulphuric acid?

Ans: Sulphuric acid is the component of acid rain after the oxidation of sulphur dioxide in the presence of water vapours in the atmosphere. Then it becomes the part of river water or may be found in some springs.

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Q3: Why sulphuric acid is a dehydrating agent?

Ans: Sulphuric acid has a great affinity for water, so it acts as a dehydrating agent.