Sulfurous Acid: Formulas, Main Uses and Precautions

He Sulphurous acid Is a non-flammable chemical, more specifically a mineral acid (not an organic acid) that is formed as a result of the dissolution of sulfur (IV) oxide in water.

Among its physical properties it can be emphasized that it is a colorless, unstable liquid soluble in water, has a strong and suffocating sulfur odor, is highly corrosive and a potent reducing agent.


As a gas it is colorless and has a pungent odor, its boiling point is equal to -10 ° C and solidifies to -76 ° C.

This chemical compound ends with the suffix"bear"because it presupposes that it is a compound belonging to the oxoacids (acids containing oxygen) and works with valence 4 and is formed by:

  • 2 hydrogen atoms.
  • 1 sulfur atom.
  • 3 oxygen atoms.

Sulfuric acid does not immediately convert to sulfuric acid when it is present in the presence of oxygen in the air, but it does occur partially when atmospheric moisture also intervenes.

Where is it located

Sulfuric acid is present in nature, either released by the openings of some volcanoes, mineral waters (in their dissolution), in some plants and also in acidic rains that form after the combination of sulfur dioxide (SO2) (Commonly emitted by large factories, fossil fuels and explosion engines) with the water present in the atmosphere, after which it returns to the earth in the form of acid rain (rain with dissolved acids).

Obtaining sulfurous acid

This compound must be studied under three states: gaseous, liquid and dissolved sulfuric acid in water.

It is not a permanent gas, it can pass to liquid state and also solidify if it is subjected to the simultaneous action of a strong pressure and cold.

  • Gaseous sulphurous acid: the obtaining of this body is presented by two procedures:
  1. Burn sulfur in the air or oxygen.
  2. By eliminating an equivalent of oxygen of the three that owns the sulfuric acid.

The sulphurous acid gas has a density of 2.266, is colorless and very soluble in water.

A volume of water dissolves about 50 volumes of sulfurous acid and alcohol dissolves 115 volumes at a temperature of 20 ° C and pressure of 0.760 (considered normal).

As it is considered unfit for combustion, it must be treated with great care because it can cause serious accidents if it is inhaled and is lodged in the respiratory system, in addition it produces a strong cough (in this case, you should immediately look for a place to breathe air More pure), can also irritate and burn the eyes and skin, cause eye damage, irritate the throat and nose.

Because it is a bad gas it is very useful to extinguish fires of small magnitude.

It decomposes the coloring matter by removing oxygen and thus causing discoloration of many plant substances (this property is commonly used for bleaching cotton, wool, etc.)

  • Liquid sulfuric acid : Sulphurous gas can be settled at ordinary pressure if it is subjected to a cold of -10 ° C.

It is colorless, very light, boils at a temperature of -8 ° C and has a density of 1.45.

If it is suddenly evaporated, it can produce a powerful cold capable of freezing the mercury and liquidating several gases (chlorine, ammonia, etc.)

Liquid sulfuric acid can be solidified by subjecting it to a temperature of -100 ° C.

  • Water saturated with sulfuric acid gas : The dissolution of sulphurous acid has all the characteristics and properties of the gas with a density of 1.04 and must be reserved for contact with air because it rapidly absorbs oxygen and is converted into sulfuric acid.

Importance and main uses of sulfurous acid

  • It is used for the synthesis of chemical and medicinal products.
  • For bleaching in large quantities or extensions (wool, cotton, silk, etc.) and / or bleaching stains of materials ruined by chlorine.
  • It is used to remove stains of wine or fruit from linen or clothing.
  • At some point it was used to carry out fumigation in order to disinfect vessels, belongings of epidemic patients, etc.
  • Sulfur gas was considered effective in combating mange (for more than two centuries).
  • To avoid acidic fermentation of alcoholic liquids (wine, beer).
  • Disinfectant properties.
  • Paper making.
  • Commonly used as a preservative in fruits and vegetables.
  • Antiseptic.

Ways to avoid or reduce exposure to sulphurous acid

  • Whenever possible, perform operations involving this compound in a well ventilated area; otherwise, use respirator masks.
  • Wear protective clothing.
  • Wash immediately after being exposed to this chemical and / or at the end of the working round.
  • Place caution notices in the work area.
  • Educate and train workers by communicating all the necessary information for the prevention of possible accidents related to this compound, especially if they are constantly exposed.
  • If a worker's clothing has been contaminated by this acid, it must be changed immediately.
  • When in contact with the skin you should shower immediately to remove the chemical.
  • Do not eat, smoke or drink near the area where you work, handle, process or store sulfuric acid (this may be inferred unintentionally). Wash hands before performing all the previously mentioned activities and before using the bathroom.
  • Wear safety goggles (or full face shield, if necessary).


(Semi-developed formula)

Systematic nomenclature Trioxosulfato (IV) of hydrogen
Stock nomenclature Trioxosulfuric acid (IV)
Traditional nomenclature Sulfuric acid
Type of compound Oxoacid

Physical properties

Appearance Colorless
Density 1030 kg / m 3; 1.03 g / cm 3
Mass Molar 82.07 g / mol
Solubility Very soluble (in water and alcohol)
Odor Strong, sulfurous, suffocating
Melting point -76Â ° C
Boiling point -10 ° C

Compounds Related

Sulfur Oxide (II)
Sulfur Oxide (IV)
Sulfur Oxide (VI)
Sulfuric acid
Peroxosulfuric acid
Peroxodisulfuric acid
Safety precautions
Ingestion May cause severe and permanent damage
Inhalation Causes respiratory tract irritation
Skin Causes burns
Eyes Causes burns


  1. Craig, Bruce & Anderson, David. (2002). Second Edition"Handbook of Corrosion Data".
  2. Muñoz de Luna, D.R.T. (1864). "Elementary Lessons in General Chemistry". Second Edition, Volume I.
  3. EcuRed. "Sulfurous Acid". Taken from

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