Dive Deeper
- 🌫️ What Is Carbon Dioxide?
- 💧 What Happens When Gases Dissolve in Water?
- 🧪 How CO₂ Reacts with Water
- 🍋 CO₂ and Acidity: Why It Makes Water Sour
- 🌊 Ocean Acidification: The Big Impact
- 🎯 Final Thoughts
- 📚 References
🌫️ What Is Carbon Dioxide?
Carbon dioxide (CO₂) is a gas made of one carbon atom and two oxygen atoms. It’s found in the air we breathe out, in soda bubbles, and when things like wood or gas burn. Even though we usually think of it as a gas, carbon dioxide can dissolve in water — and when it does, some pretty cool chemistry takes place.
You might have already experienced it. Ever tasted sparkling water or soda? That fizzy tingle on your tongue comes from carbon dioxide reacting in the water!
💧 What Happens When Gases Dissolve in Water?
When a gas like CO₂ dissolves in water, it mixes with the water molecules. This is called dissolution. But carbon dioxide is special because it doesn’t just dissolve — it reacts with the water, too.
Dissolving vs. Reacting
- Dissolving = just mixing without changing
- Reacting = forming new substances
So when CO₂ goes into water, part of it simply dissolves, but another part reacts chemically to create new compounds.
🧪 How CO₂ Reacts with Water
When carbon dioxide enters water, it forms a weak acid called carbonic acid (H₂CO₃). This happens through a chemical reaction:
CO₂ + H₂O ⇌ H₂CO₃
This equation means carbon dioxide reacts with water to make carbonic acid, but the reaction can go both ways. That’s why the double arrows (⇌) are used — it’s a reversible reaction.
Once carbonic acid forms, it can break apart into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). These ions make the water more acidic.
🔬 Chemical Reactions:
- CO₂ + H₂O ⇌ H₂CO₃ (carbonic acid)
- H₂CO₃ ⇌ H⁺ + HCO₃⁻ (bicarbonate ion)
- HCO₃⁻ ⇌ H⁺ + CO₃²⁻ (carbonate ion)
These tiny reactions change the pH of the water — which is a measure of how acidic or basic a liquid is.
🍋 CO₂ and Acidity: Why It Makes Water Sour
When carbonic acid forms in water, it releases hydrogen ions (H⁺). These ions are what make things taste sour and feel tingly, like in fizzy drinks.
pH and Acidity
- Low pH = more acidic
- High pH = more basic (or alkaline)
- Neutral water has a pH of about 7
- When CO₂ is added, the pH drops to around 5 or 6
📉 Stat Box: Regular tap water has a pH of about 7, but sparkling water has a pH closer to 5 — making it about 100 times more acidic [1].
🌊 Ocean Acidification: The Big Impact
When carbon dioxide dissolves in the ocean, it reacts the same way — forming carbonic acid. But in large amounts, this causes a serious environmental problem called ocean acidification.
Effects of Ocean Acidification:
- Harms marine life: Shellfish like clams and corals need carbonate ions to build their shells. But when CO₂ rises, there are fewer carbonate ions left.
- Weakens shells and skeletons
- Changes ocean chemistry
🧭 Fact: According to NOAA, the ocean absorbs about 30% of all CO₂ humans release into the air [2].
That might sound helpful, but it’s creating water that’s too acidic for many ocean creatures to survive.
🎯 Final Thoughts
When carbon dioxide dissolves in water, it’s more than just gas mixing with liquid — it starts a chemical reaction that creates carbonic acid, changes the water’s pH, and makes it more acidic. This explains why soda tastes tangy and why rising CO₂ levels are affecting the oceans.
From fizzy drinks to coral reefs, CO₂ in water plays a major role in both our daily lives and the environment. Understanding how this simple gas changes water helps us see how chemistry connects to the world around us.
📚 References
- American Chemical Society. “Why Does Carbonated Water Taste Sour?” https://www.acs.org
- National Oceanic and Atmospheric Administration (NOAA). “Ocean Acidification.” https://oceanservice.noaa.gov/facts/acidification.html
- Britannica. “Carbonic Acid.” https://www.britannica.com/science/carbonic-acid
- LibreTexts Chemistry. “Carbon Dioxide in Water.” https://chem.libretexts.org