IGCSE Chemistry 2026 – 400 Free Practice Questions to Pass the Exam

Carbon dioxide and sulfur dioxide are classified as acidic because when they dissolve in water, they form acids. Carbon dioxide reacts with water to form carbonic acid, a weak acid, leading to a decrease in pH when dissolved in aqueous solutions. Sulfur dioxide, on the other hand, reacts with water to yield sulfurous acid, which is also an acid. The ability of these gases to form acids in solution is the primary reason they are categorized as acidic.

Understanding the behavior of these compounds in water highlights their impact on environmental chemistry as well, particularly in relation to acid rain, which is formed when sulfur dioxide and nitrogen oxides react with atmospheric moisture. This classification is significant in assessing the environmental implications of pollutants and their role in acid-base chemistry.