Calcium oxide (CaO), also known as quicklime, is slightly soluble in water.
Understanding Calcium Oxide Solubility
While not highly soluble, calcium oxide does dissolve in water to a certain extent. The provided reference indicates its solubility at different temperatures:
- At 25°C: 1 gram of calcium oxide dissolves in 840 milliliters of water.
- At 100°C: 1 gram of calcium oxide dissolves in 1,740 milliliters of water.
This clearly shows that calcium oxide’s solubility decreases as the temperature of the water increases.
Calcium Oxide: Properties and Reactivity
- Calcium oxide is a hard, white or grayish-white material.
- It's often found as a porous pebble or powder.
- It's odorless.
- It exhibits "quick slaking", meaning it reacts vigorously with water.
The Reaction with Water
When calcium oxide reacts with water (H₂O), it forms calcium hydroxide (Ca(OH)₂), also known as slaked lime. This reaction is exothermic, meaning it releases heat.
CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + heatWhile the reaction forms calcium hydroxide, which is also only slightly soluble, the initial dissolution of the calcium oxide is what we are addressing here when asking if calcium oxide is soluble. This distinction is important as the reaction changes the chemical composition of the substance.
Solubility of Calcium Oxide at a Glance
| Temperature (°C) | Water Volume (mL) | Calcium Oxide Dissolved (g) |
|---|---|---|
| 25 | 840 | 1 |
| 100 | 1,740 | 1 |
This table demonstrates the inverse relationship between temperature and the solubility of calcium oxide.
Practical Insights
- The reaction with water (slaking) is how calcium oxide is converted into calcium hydroxide for various applications, like in mortar and plaster.
- The slight solubility of calcium oxide in water explains why it doesn't readily dissolve away in moist environments.
- The decrease in solubility at higher temperatures is unusual for many substances.
