Can CaO dissolve in water

Calcium oxide doesn't truly dissolve in water in the conventional sense—instead, it reacts vigorously with water in an exothermic chemical reaction to form calcium hydroxide, Ca(OH)2. When you add CaO to water, you're not creating a solution of calcium oxide; you're triggering a chemical transformation. The process involves the CaO breaking apart and bonding with water molecules to create an entirely different compound, accompanied by significant heat release and often steam formation. This is fundamentally different from substances like salt or sugar that dissolve by dispersing their molecules or ions throughout water while maintaining their chemical identity.

The resulting calcium hydroxide has limited solubility in water—only about 1.5 grams per liter at room temperature—which means it forms a slightly cloudy suspension called limewater rather than a clear solution. This distinction matters significantly in practical applications: in construction, when quicklime is "slaked" by adding water, workers are managing a chemical reaction, not a dissolution process, which is why temperature control and gradual addition are critical safety measures. The reaction's vigor and heat output distinguish it from simple dissolution, making CaO's interaction with water a textbook example of why chemists differentiate between physical processes (like dissolving) and chemical reactions (like the formation of calcium hydroxide).