Intermediate Topic 657 of 1102 Inorganic Chemistry
Sulfur Dioxide
A pungent gas formed from burning sulfur compounds, a cause of acid rain and a preservative.
In-depth explanation of Sulfur Dioxide
Sulfur dioxide, SO2, is a colourless, toxic gas with a sharp smell and a bent molecule with an O-S-O angle of about 119 degrees. It forms when sulfur is burned or sulfide ores are roasted, and it dissolves in water to give the weak acid H2SO3. It acts as a reducing agent and as a bleach, and it inhibits bacteria, so it is used as a food preservative under code E220. Its emissions contribute to acid rain, because SO2 is oxidized in the atmosphere to sulfuric acid.
Going deeper: Sulfur Dioxide
Key ideas: Made by burning S or roasting sulfides: 4FeS2 + 11O2 gives 2Fe2O3 + 8SO2. It is bent with S-O bond order 1.5, is a reducing agent (decolorizes acidified KMnO4, turns dichromate green), and also bleaches by reduction, temporarily. Its solution gives sulfurous acid H2SO3, pKa1 about 1.8. Is the main cause of acid rain, with SO3 and H2SO4 formed in air.
Common mistakes and connections: Students say SO2 bleaches like chlorine; chlorine bleaches by oxidation permanently, SO2 by reduction, and the color often returns in air. SO2 turns lime water milky like CO2, so distinguish by KMnO4 or dichromate decolorization. Links to contact process, acid rain and redox.
Visualization of Sulfur Dioxide
Bent SO2 with an O-S-O angle near 119 degrees; it dissolves to give weak H2SO3 and contributes to acid rain. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Burning sulfur in air gives sulfur dioxide: S + O2 giving SO2.
Frequently asked questions about Sulfur Dioxide
What is Sulfur Dioxide?
A pungent gas formed from burning sulfur compounds, a cause of acid rain and a preservative.
Is Sulfur Dioxide a beginner, intermediate or advanced topic?
Sulfur Dioxide is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Sulfur Dioxide?
Study these earlier topics in Inorganic Chemistry first: Ozone, Oxides, Sulfur Allotropes.
What comes after Sulfur Dioxide?
The next topics in Inorganic Chemistry are Sulfuric Acid and Halogens.
Can I practise Sulfur Dioxide with quizzes?
Yes. The interactive lesson includes a self-check question on Sulfur Dioxide, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Sulfur Dioxide fits in Inorganic Chemistry
Sulfur Dioxide is topic 42 of 113 in Inorganic Chemistry.