Sulfurous Acid: Overview, Questions, Preparation

Sulfurous acid is formed in nature when sulfur dioxide reacts with atmospheric moisture. It is a chemical compound that is associated with acid rain. 

Preparation

You can prepare sulfurous acid by dissolving sulfur dioxide in water. The chemical reaction that occurs makes the water acidic, and the resulting solution is called sulfurous acid. However, this reaction is reversible. As sulfurous acid is weak and unstable in nature, it can readily revert to its constituent sulfur dioxide (SO2) and water (H2O)

SO2 + H2O = H2SO3

Physical properties

Sulfurous acid has a pungent odour and is colourless. It has a boiling point of -60°C and has a density of 1.03 g/mL.

Chemical properties

Sulfurous cannot be isolated in its pure state. An aqueous solution of sulfur dioxide hardly contains sulfurous acid.  It is also a weak and unstable dibasic acid that breaks down into water and sulfur dioxide readily. 

H2SO3 (aq) =  H2O + SO2

• Used as reducing and disinfecting agents 
• Used for bleaching
• Used for bleaching materials that are sensitive to chlorine
• Used as solutions of sulfite and bisulfite salts
• Used as a fruit and vegetable preservative
• Used in making paper and wine

Sulfurous acid is a corrosive chemical. It can irritate and cause a burning sensation in the skin and eyes. Excess exposure can cause eye damage. 

Inhaling sulfurous acid causes shortness of breath and coughing. 

Sulfurous acid decomposes and releases a toxic gas called sulfur dioxide. It can also turn into a corrosive acid called sulfuric acid when exposed to air.

Ingestion, inhalation, or skin exposure to sulfurous acid may cause eye injury, burns, and respiratory problems. 

Class 12 Sulfurous Acid

You will study sulfurous acid in Unit 7 - The p-Block Elements.  In this chapter, you will learn about the allotropic forms of sulphur and its important compounds. 

Weightage of the topic in the exam

This topic, Sulfurous acid, belongs to a group of units with a total weightage of 16 marks in the class 12 board exams. 

Q. Is sulphurous acid a strong or weak acid?

Q. Is sulfurous acid a strong electrolyte?

Q. Does sulfurous acid have ionic or covalent bonds?

Q> Who discovered sulfurous acid?

Q. What is the difference between sulfurous acid and sulfuric?