Yes, while CO2 itself isn't an acid in the traditional sense (it doesn't contain hydrogen ions, H+), it reacts with water to form carbonic acid (H₂CO₃), which does increase acidity. This is why dissolved CO2 lowers the pH of water, making it more acidic.
Understanding CO2's Acidity
- CO2 as a Lewis Acid: CO2 acts as a Lewis acid because it can accept lone electron pairs, as noted in one of the references. This is a different definition of acidity than the Brønsted-Lowry definition which focuses on proton (H+) donation.
- Reaction with Water: The crucial aspect of CO2's acidity is its reaction with water (H₂O): CO₂ + H₂O ↔ H₂CO₃. This equilibrium reaction produces carbonic acid, which then partially dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺). The presence of these hydrogen ions is what lowers the pH and increases acidity.
- Ocean Acidification: A prominent example of CO2's effect on acidity is ocean acidification. Increased atmospheric CO2 dissolves into the ocean, forming carbonic acid and lowering the ocean's pH. This harms marine life that relies on carbonate ions for shell and skeleton formation. Multiple sources, such as NOAA and the Smithsonian Ocean, confirm this process.
Examples
- Rainwater: Rainwater naturally absorbs CO2 from the atmosphere, leading to slightly acidic rain (pH around 5.6).
- Soda: Carbonated beverages contain dissolved CO2, making them acidic and fizzy.
Conclusion
CO2's impact on acidity stems from its reaction with water to form carbonic acid, subsequently releasing hydrogen ions and lowering the pH. While not directly an acid in all definitions, its effects are unequivocally acidic.
