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

Which property of carbon dioxide indicates its state concerning water?

1. Insoluble in water

2. Soluble in water

3. Highly reactive with water

4. Completely volatile in water

The correct answer is: Soluble in water

The correct choice highlights that carbon dioxide (CO₂) is known for being soluble in water. This property is significant because it allows CO₂ to interact with water and form carbonic acid (H₂CO₃), even though it does not dissolve in water to the same extent as substances like sodium chloride (table salt). The solubility of carbon dioxide in water plays a vital role in various natural processes, such as the carbon cycle and the buffering system in biological systems, including the oceans. When carbon dioxide dissolves in water, it can also affect the pH of the solution. This is especially relevant in environmental chemistry, such as ocean acidification, where increased CO₂ levels decrease marine pH levels due to the formation of carbonic acid. Other choices suggest different properties that do not accurately reflect the behavior of carbon dioxide in water. For instance, being completely volatile in water would imply that CO₂ evaporates easily from the water, which contradicts its nature as a solute. Similarly, stating that it is highly reactive with water is misleading, as CO₂’s reaction is primarily a physical dissolution and not a vigorous chemical reaction. Additionally, asserting that it is insoluble in water does not hold true, as this suggests that CO