Sulfur dioxide is an acidic, toxic gas and with a rotten smell characteristics. Sulfur can be prepared by several ways. In this tutorial, we will learn a wide range of facts about sulfur dioxide gas including properties, preparation methods, reactions and etc.
There are only three atoms in SO2 molecule. Both oxygen atoms have made double bonds with only sulfur atom. There is one lone pair on the sulfur atom.
Here, we are going to learn about physical and chemical properties of sulfur dioxide.
We cannot see a colour in SO2 gas and it is a colourless gas. Therefore we cannot identify it by it's colour from other gases. Human nose can identify the pungent odor of sulfur dioxide. SO2 is heavier than air.
Sulfur, metal sulfide, metal sulfite compounds, sulfuric acid can be used to prepare sulfur dioxide gas with other different compounds at different physical conditions. These preparation methods are implemented in laboratory scale and industrial scales as required.
There are so many methodologies to produce sulfur dioxide gas in your laboratory.
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.
Solid metal sulfite compounds react with dilute acids and give SO2.
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.
Sulfur is heated with concentrated sulfuric acid. Sulfur is oxidized to sulfur dioxide and sulfuric acid is reduced to sulfur dioxide.
Carbon is oxidized to carbon dioxide (CO2) and sulfuric acid is reduced to SO2.
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.
Sulfur dioxide gas in product as an intermediate product during the sulfuric acid manufacturing process. Sulfur or metal sulfide is burnt to produce SO2 gas.
In this section, we are going to look how sulfur dioxide gas reacts with other chemicals. Sulfur dioxide can be oxidized or reduced to other sulfur compounds.
Sulfur dioxide is averagely soluble in water and reacts reversibly with water molecules to form Sulfurous acid which is a weak acid. Sulfurous acid partially dissociates in two steps to produce Hydronium ions (H3O+) as shown below.
Sulfur dioxide is not easily oxidized to sulfur trioxide (SO3). In sulfuric acid manufacturing process, sulfur dioxide is converted to sulfur trioxide at 4500C temperature in the presence of Platinum or vanadium oxide catalyst.
However, if sulfur dioxide is oxidized to sulfur trioxide by oxygen gas and dissolve in water, small quantities of sulfuric acid (H2SO4) is given because sulfur trioxide's solubility in water is much poor than sulfur dioxide gas.
Formation of sulfurous acid or sulfuric acid as explained earlier is a direct reasons for acid rains which is one of the major environmental pollution method.
Sulfur dioxide is reduced to sulfur while permanganate ion is reduced to Manganese +2 cation during the reaction. Due to the formation of sulfur , you will see white-yellow colour powder is deposited in the solution. As well, purple colour solution (due to potassium permanganate) is changed to colourless or pale pink colour as results.
As mentioned earlier reaction, Sulfur dioxide is reduced to sulfur while dichromate ion is reduced to Chromium +3 cation during the reaction. Due to the formation of sulfur, you will see white-yellow colour powder is deposited in the solution. As well, orange colour solution (due to potassium dichromate) is changed to colourless or green colour as results.
Sulfur dioxide gas reacts with hydrogen sulfide gas and gives sulfur and water as products.This reaction is a reversible reaction.
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
Copper is oxidized to Cu2+ while H2SO4 is reduced to sulfur dioxide which is a colouress gas.