Preparation of Sulfur Dioxide and Characteristics | SO2

Sulfur dioxide is an acidic, toxic and has an rotten smell characteristics. It can be prepared by burning sulfur or metal sulfide compound or hydrogen sulfide with oxygen. Sulfuric acid can be reduced to sulfur dioxide because sulfuric acid is an oxidizing acid. It is used in many industrial applications.

sulfur dioxide molecule shape

Characteristics of SO2

Here, we are going to learn about few characteristics of sulfur oxide and their effects.


SO2 is an acidic gas which dissolve in water to produce sulfurous acid (H2SO3). It is a weak acid.

If, SO2 is oxidized to SO3 by O2 and dissolve in water, sulfuric acid (H2SO4) is given.

This causes to acid rain which is one of the major environmental pollution method.

Colourless, pungent odor

We cannot see a colour in SO2 gas. Therefore we cannot identify it by colour. Human nose can identify this pungent odor. SO2 is heavier than air.


0 - 0.1 ppm range is not dangerous. But more than that, it causes many health problems. Over 5 ppm, warnings of emergency situations should be activated.

Sulfur dioxide effects on health

Preparation of sulfur dioxide

Sulfur, metal sulfide, metal sulfite compounds, sulfuric acid can be used to prepare sulfur dioxide gas with other different compounds at different physical conditions.

Burning sulfur or metal sulfide or hydrogen sulfide

This method is used to prepare SO2 in industry to manufacture sulfuric acid. Sulfur (s), hydrogen sulfide (H2S) or metal sulfide (Na2S) can be used to produce SO2.

burning sulfur, hydrogen sulfide, metal sulfides to produce sulfur dioxide

Hot concentrated sulfuric acid and Copper | H2SO4 + Cu

Add concentrated sulfuric acid to copper and heat the solution. Then sulfur dioxide, copper sulfate (CuSO4) and water are given as products. CuSO4 is blue colour.

copper and hot concentrated sulfuric acid reaction

Dilute acids and metal sulfite

Solid metal sulfite compounds react with dilute acids and give SO2.

metal sulfite and dilute acid reaction

Dilute acid and thiosulfate reaction | S2O32- + H+

Add a dilute acid to metal thiosulfate ( S2O32-). It gives SO2 and sulfur which is deposited as a pale yellow solid. This reaction is used to identify thiosulfate ion from sulfate ion in qualitative analysis.

sodium thiosulfate and hydrochloric acid - Na2S2O3 + HCl

Sulfur and hot concentrated sulfuric acid | S + H2SO4

Sulfur is heated with concentrated sulfuric acid. Sulfur is oxidized to sulfur dioxide and sulfuric acid is reduced to sulfur dioxide.

Sulfur and hot concentrated sulfuric acid - S + H2SO4

Carbon and hot concentrated sulfuric acid | C + H2SO4

Carbon is oxidized to carbon dioxide (CO2) and sulfuric acid is reduced to SO2.

carbon and hot concentrated sulfuric acid - C + H2SO4

Sulfur dioxide producing industries

Petroleum Industry

- Crude oil contains sulfur as different compounds. These sulfur is removed or reduced in refining process. But some fuels contains little bit sulfur amount. When fuel oil is burnt in furnaces to generate the heat, SO2 is released. Sulfur in the crude oil is converted to H2S in sulfur removing process. If H2S is not used to produce another product such as sulfuric acid, H2S is burnt. It also produces SO2.

Sulfuric Acid Manufacturing - Contact process

S or metal sulfide is burnt to produce SO2.


Cu + concentrated H2SO4

Copper is oxidized to Cu2+ while H2SO4 is reduced to sulfur dioxide which is a colouress gas.

Lewis structures

P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure