International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is the chemical equation for sulfur dioxide dissolving in water to form acid rain?

1. SO₂ + H₂O -> H₂SO₃

2. SO₂ + O₂ -> H₂SO₄

3. SO₂ + H₂O -> H₂SO₄

4. SO₂ + N₂ -> H₂SO₃

The correct answer is: SO₂ + H₂O -> H₂SO₃

The correct answer is based on the chemical interaction of sulfur dioxide with water to produce an acid. When sulfur dioxide (SO₂) dissolves in water (H₂O), it reacts to form sulfurous acid (H₂SO₃). This reaction is important in the context of acid rain because it highlights how sulfur dioxide emissions can contribute to the acidity of precipitation. The formation of sulfurous acid (H₂SO₃) occurs in the following way: 1. Sulfur dioxide is a gas that can easily dissolve in water. 2. When it comes into contact with water, a chemical reaction takes place where sulfur dioxide combines with water molecules. 3. This results in the formation of H₂SO₃, which is a weak acid. This process is significant as it shows how emissions from combustion processes, such as those from vehicles and industrial plants, can lead to environmental issues like acid rain, which can harm ecosystems, buildings, and water sources. The other options do not accurately represent the primary reaction of sulfur dioxide in water leading to acid rain. For instance, some suggest the formation of sulfuric acid (H₂SO₄) which is produced through further oxidation processes but is not the direct result of SO₂ reacting with H