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

What is the relationship between acid rain and limestone?

1. Acid rain promotes the growth of limestone

2. Acid rain erodes limestone structures

3. Acid rain neutralizes acid in limestone

4. Acid rain has no effect on limestone

The correct answer is: Acid rain erodes limestone structures

Acid rain has a significant impact on limestone, primarily through the process of erosion. Limestone is primarily composed of calcium carbonate, which reacts with the acids present in acid rain, such as sulfuric acid and nitric acid. When acid rain falls on limestone, a chemical reaction occurs that leads to the dissolution of calcium carbonate, resulting in the erosion of limestone structures over time. This erosion can damage natural formations such as caves and cliffs, as well as human-made structures such as buildings and monuments made from limestone. The dissolution process not only weakens these structures but also contributes to the formation of features like karst landscapes, which are characterized by deep valleys, sinkholes, and underground rivers formed by the ongoing erosion of limestone. In contrast, the other options do not accurately reflect the interaction between acid rain and limestone. Acid rain does not promote the growth of limestone, nor does it neutralize it. Additionally, claiming that acid rain has no effect on limestone ignores the well-documented chemical reactions between the two. Thus, the assertion that acid rain erodes limestone structures is a clear and scientifically supported understanding of their relationship.