MCQ Detailed View

Limestone is primarily composed of calcium carbonate (CaCO₃). When limestone reacts with water containing carbonic acid (H₂CO₃), a chemical reaction occurs that releases carbon dioxide (CO₂) gas. The reaction can be represented as:

CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂

This reaction is important in geology and environmental chemistry because it explains the formation of caves and karst landscapes through the dissolution of limestone. When water containing dissolved CO₂ comes in contact with limestone, the solid calcium carbonate slowly converts into soluble calcium bicarbonate, and CO₂ is released.

The gas released is carbon dioxide, which is colorless, odorless, and heavier than air. Carbon dioxide is different from hydrogen, oxygen, or nitrogen, which are not produced in this reaction. Hydrogen is typically released in reactions with acids like hydrochloric acid and metals. Oxygen is released in decomposition reactions such as hydrogen peroxide breakdown, and nitrogen is generally inert in these types of reactions.

This reaction also has practical applications. Carbon dioxide released from limestone is used in cement and lime industries, and the reaction plays a role in natural carbon cycling in soil and water systems. Understanding the behavior of limestone with water helps students learn about inorganic reactions, gas evolution, and acid-carbonate chemistry.

In summary, the reaction of limestone with water results in the formation of calcium bicarbonate and the release of carbon dioxide gas, making it a key example of gas-evolving reactions in Inorganic Chemistry.