Is NH3 or CO2 more soluble in water?

Why Ammonia (NH3) Is More Soluble in Water Than CO2

When comparing the solubility of gases in water, chemical behavior matters more than just physical dissolution. Ammonia (NH3) is significantly more soluble in water than carbon dioxide (CO2), and the key reason lies in how these molecules interact with water molecules.

Ammonia doesn’t just dissolve—it reacts. Upon entering water, NH3 accepts a proton, forming ammonium ion (NH4+) and hydroxide ion (OH–). This acid-base reaction makes the process highly favorable, greatly increasing solubility. Because NH3 ionizes in water, its interaction goes beyond simple physical mixing, effectively locking more molecules into solution.

CO2 also reacts with water—but less efficiently. It forms carbonic acid (H2CO3), which quickly dissociates into bicarbonate and hydrogen ions. However, this reaction is slower and less complete compared to ammonia’s protonation. Without a strong dipole or immediate ionization like NH3, CO2 relies more on weaker intermolecular forces, limiting its solubility.

Another factor is polarity. NH3 is highly polar and forms strong hydrogen bonds with water, further enhancing its solubility. CO2, though slightly polar in its bent ionic forms, is mostly nonpolar in its linear, gaseous state, making it less compatible with polar water molecules.

Ultimately, the ability of NH3 to ionize and form stable ions in solution gives it a clear edge. While both gases interact chemically with water, ammonia’s rapid and complete reaction, combined with strong hydrogen bonding, makes it far more soluble than CO2 under similar conditions.