How did H2SO4 become an acid

In nature, sulfuric acid occurs in acid rain and in solfataras. The commercially available 96% sulfuric acid is a heavy, oily liquid. It can be mixed with water as required. With increasing, aqueous dilution, the strong acid first splits off one proton; with greater dilution, the second proton also dissociates. In the first step, a hydrogen sulfate ion HSO is formed4, in the second step a sulfate ion SO42−:

1st step: H2SO4 + H2O HSO4 + H3O+ 
2nd step: HSO4 + H2O SO42− + H3O+ 
3rd step: H2SO4 + 2 H.2O SO42− + 2 H.3O+ 

The density varies depending on the concentration. When distilling dilute solutions, the water first evaporates, and a sulfuric acid with a maximum concentration of 98.3% is obtained. This concentrated sulfuric acid forms an azeotropic mixture that boils constantly at +338 ° C. If you continue to heat, only this mixture goes into the distillate. Different solutions in water are common:

Mass percentage
Amount of substance
at 20 ° C
96 %17.966 mol / l
"concentrated"1.8355 g / cm3
38 %4.981 mol / l"Battery acid"1.2855 g / cm3
10 %1.087 mol / l"Diluted"1.0661 g / cm3

Sulfuric acid is very hygroscopic and attracts moisture from the air. When mixing with water, which takes place with strong heat development, it may only be poured into the water: "Never put water on the acid, otherwise the monster will happen!". If you add water to concentrated sulfuric acid, the mixture can heat up so much that it begins to boil and the sulfuric acid squirts out of the vessel.

"If you put water on the acid, then the monstrous happens".


The concentrated acid destroys organic substances such as sugar, cotton fabric or skin with the formation of black carbon. If you put concentrated sulfuric acid on grape sugar in a beaker, it removes hydrogen and oxygen from the carbohydrate, so that only the carbon structure of the sugar remains.

Concentrated sulfuric acid reacts with sugar.


Concentrated sulfuric acid on the skin should be wiped off immediately with a dry cloth and only then treated with plenty of water. It causes life-threatening burns in the stomach. Vomiting must not be induced. Countermeasures include drinking water or neutralizing the acid with a mixture of water and magnesium oxide:

MgO + H2SO4 MgSO4 + H2O
Diluted sulfuric acid reacts with base metals to form hydrogen and the corresponding metal salts. This creates the sulfates, the salts of sulfuric acid:

Mg + H2SO4(aq)  MgSO4 + H2  
Zn + H2SO4(aq) ZnSO4 + H2  

Magnesium, zinc and copper in dilute sulfuric acid.

Diluted sulfuric acid does not react with compact copper. Only hot, concentrated sulfuric acid reacts with the metal, but not with the evolution of hydrogen, but with the formation of copper sulfate, sulfur dioxide and water:

Cu + 2H2SO4  CuSO4 + SO2 + 2 H.2O  

This type of reaction also occurs with silver and mercury. The precious metals gold and platinum are not attacked by concentrated sulfuric acid. Iron and lead also resist concentrated sulfuric acid. Iron is passivated and the lead forms an insoluble coating of lead sulfate. It can therefore be safely stored in lead vessels or transported in iron pipes.

The pure, 100% sulfuric acid dissolves the gas sulfur trioxide SO3 with formation of disulfuric acid:

SO3 + H2SO4  H2S.2O7 

A mixture of sulfuric acid and disulfuric acid was called "oleum" or "vitriol oil" by the alchemists. Today it is also known as "smoking sulfuric acid". In this acid, sulfur trioxide is constantly released, which reacts with the humidity in the air and forms a mist in the process. It is produced as an intermediate product in sulfuric acid synthesis.

The production of sulfuric acid by the alchemists probably goes back to the 13th century. When glowing “vitriols” from iron or copper sulphate, they received the “oleum vitrioli” (smoking sulfuric acid) and when burning sulfur with nitric or potassium nitrate the “oleum sulphuris” (diluted sulfuric acid). Both manufacturing options were developed by Andreas Libavius ​​(born around 1540) in his work published in 1597 Alchemia described. The production process from vitriols was used until the 19th century. The advantage was that you got a very concentrated acid.
With the invention of the lead chamber process by Roebuck and Garbett in Birmingham, it was possible to produce sulfuric acid on an industrial scale from 1774 onwards. A mixture of sulfur dioxide, air and nitrogen oxides was heated to about 400 ° C. in a reaction tower lined with fire bricks. The resulting gas mixture then came into several lead-lined containers connected in series, where it was sprinkled with water and in the process reacted to form 60 to 70% sulfuric acid. A lead lining was used, as this was the only cheap metal at the time that was not attacked by concentrated sulfuric acid. In the period that followed, the lead chamber process was improved.
Another option is production from metal sulphates using the Müller-Kühne process. Here, gypsum or anhydrite in a mixture with clay, sand and coal is split into sulfur dioxide and calcium oxide in rotary kilns, at the same time carbon dioxide is produced:

2 CaSO4 + C 2 CaO + 2 SO2 + CO2  

Today, sulfuric acid is mainly produced using the contact process. The sulfur dioxide required for this was previously obtained by roasting the mineral pyrite. Today, sulfur dioxide is mainly obtained by burning sulfur, which can be obtained from the processing of natural gas. The process can be described in a somewhat simplified way: The sulfur dioxide is oxidized to sulfur trioxide in a first contact furnace. This is mixed with 96% sulfuric acid and passed into water. In the double contact process, any remaining sulfur dioxide is oxidized in a second contact furnace after the first pass.

Sulfuric acid synthesis by roasting pyrite in a model experiment.

Sulfuric acid is used to produce sulfates and fertilizers, and mixed with nitric acid as a nitrating acid to produce explosives. In lead batteries it is present as an electrolyte: the 37 to 38% acid has the best conductivity for electrical current. Sulfuric acid is an important catalyst in the laboratory and in chemical synthesis. Their importance as a raw material for detergent and dye production, for example in sulphonation and sulphation, is of great benefit. It is also used to break down titanium minerals in the production of the white pigment titanium dioxide. In the chemical laboratory it is a very important acid for drying substances.

A lead accumulator for a motorcycle battery is filled with 37% sulfuric acid.

Further information and media

The term acid in the household and in chemistry, sulfates
Demonstrations on the corrosivity of the fabrics
Student exercise: ester syntheses
Sulfuric acid synthesis in the contact process
Digital foils: acids, bases, salts

Create your own book: Basic text sulfuric acid


> Table of Contents