Preparation, Reactions, Chemical and Physical Properties of Sulfur Dioxide Gas (SO2)
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.
Content
- Lewis structure of sulfur dioxide gas molecule
- Physical properties of sulfur dioxide gas (SO2)
- Preparation of sulfur dioxide
- Preparation of sulfur dioxide in the laboratory
- Preparation or manufacturing cases of sulfur dioxide in industrial scale
- Reactions and chemical properties of sulfur dioxide gas
- Toxicity of sulfur dioxide
Lewis structure of sulfur dioxide gas molecule
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.
Characteristics and properties of sulfur dioxide (SO2) gas
Here, we are going to learn about physical and chemical properties of sulfur dioxide.
Physical properties of sulfur dioxide gas
Colourless, pungent odor
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.
Preparation of sulfur dioxide gas
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.
Preparation of sulfur dioxide in the laboratory
There are so many methodologies to produce sulfur dioxide gas in your laboratory.
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.
Dilute acids and metal sulfite
Solid metal sulfite compounds react with dilute acids and give SO2.
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.
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.
Carbon and hot concentrated sulfuric acid | C + H2SO4
Carbon is oxidized to carbon dioxide (CO2) and sulfuric acid is reduced to SO2.
Preparation or manufacturing cases of sulfur dioxide in industrial scale
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.
Petroleum industry and crude oil refining process
- - Crude oil contains sulfur in different compounds. These sulfur is removed or reduced in crude oil refining process to reduce sulfur dioxide emissions in combustion processes. But some fuels still contains little bit of sulfur quantity.
- 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 any by-product such as sulfuric acid, H2S is burnt as a waste and it again produces SO2.
Sulfuric Acid Manufacturing - Contact process
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.
Reactions and chemical properties of sulfur dioxide 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 reaction with water and forming acidic solutions
- Oxidation of sulfur dioxide to sulfur trioxide / Sulfur dioxide gas and oxygen gas reaction
- Sulfur dioxide gas and acidic potassium permanganate reaction
- Sulfur dioxide gas and acidic potassium dichromate reaction
- Sulfur dioxide gas and hydrogen sulfide reaction
Sulfur dioxide reaction with water and forming acidic solutions
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.
Oxidation of sulfur dioxide to sulfur trioxide
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 gas and acidic potassium permanganate (KMnO4) reaction
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.
Sulfur dioxide gas and acidic potassium dichromate (K2Cr2O7) reaction
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 and hydrogen sulfide reaction
Sulfur dioxide gas reacts with hydrogen sulfide gas and gives sulfur and water as products.This reaction is a reversible reaction.
Toxicity of sulfur dioxide
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 healthHave Questions?
What are the products when Cu metal + concentrated H2SO4 acid
Copper is oxidized to Cu2+ while H2SO4 is reduced to sulfur dioxide which is a colouress gas.