Why is the increasing amount of carbon dioxide being taken up by the oceans a cause for concern?

• A. The buffering action of carbonic acid (H₂CO₃) causes the pH of seawater to rise.
• B. More carbon dioxide causes an increase in carbonic acid (H₂CO₃), which leads to an increase in the concentration of carbonate ion (CO₃^2–).
• C. There is no cause for concern. Carbonic acid (H₂CO₃) is an excellent buffer and will help keep the pH of seawater constant.
• D. More carbon dioxide causes an increase in carbonic acid (H₂CO₃), which leads to a decrease in the concentration of carbonate ion (CO₃^2–).

Answer: (D)

Verified step by step guidance

1. Understand the chemical reaction: When carbon dioxide (CO2) is absorbed by seawater, it reacts with water (H2O) to form carbonic acid (H2CO3). This is represented by the equation: CO2 + H2O ⇌ H2CO3.
2. Recognize the role of carbonic acid: Carbonic acid can dissociate into bicarbonate (HCO3-) and hydrogen ions (H+), which is represented by the equation: H2CO3 ⇌ HCO3- + H+. The increase in hydrogen ions leads to a decrease in pH, making the water more acidic.
3. Consider the impact on carbonate ions: The presence of more hydrogen ions can shift the equilibrium of carbonate ions (CO32-) to form more bicarbonate ions, as shown in the equation: CO32- + H+ ⇌ HCO3-. This results in a decrease in carbonate ion concentration.
4. Understand the ecological implications: A decrease in carbonate ions affects marine organisms that rely on calcium carbonate (CaCO3) for their shells and skeletons, such as corals and shellfish. This can lead to weaker structures and threaten marine biodiversity.
5. Summarize the concern: The increasing amount of carbon dioxide in the oceans leads to ocean acidification, which decreases carbonate ion concentration, affecting marine life and ecosystems. This is why the uptake of CO2 by oceans is a cause for concern.