When calcium hydroxide (Ca(OH)2) interacts with water, it primarily undergoes a process of dissolution rather than a chemical reaction that forms new compounds. It dissolves sparingly to form a solution known as limewater. However, the provided reference, CaO + H2O → Ca(OH)2, describes the formation of calcium hydroxide itself, which is a crucial chemical reaction distinct from Ca(OH)2 simply dissolving in water.
Interaction of Calcium Hydroxide with Water
Calcium hydroxide, commonly known as slaked lime, is only slightly soluble in water. When added to water:
- Dissolution: A small amount of calcium hydroxide dissolves to form a clear, alkaline solution called limewater. This solution contains calcium ions (Ca²⁺) and hydroxide ions (OH⁻).
- Ca(OH)₂(s) ⇌ Ca²⁺(aq) + 2OH⁻(aq)
- Suspension: If excess calcium hydroxide is added, the undissolved portion forms a milky suspension known as milk of lime.
It's important to note that this is a physical process of dissolution and equilibrium, not a chemical reaction where new substances are created from calcium hydroxide and water.
The Formation of Calcium Hydroxide: Slaking of Lime
The provided reference highlights a significant chemical reaction that leads to the creation of calcium hydroxide. This process is known as the slaking of lime. It involves the reaction of calcium oxide (CaO), also called quicklime, with water.
The chemical equation for this reaction, as provided in the reference, is:
CaO(s) + H₂O(l) → Ca(OH)₂(s)This reaction is highly exothermic, meaning it releases a significant amount of heat. The product, calcium hydroxide, is a white powder or colorless crystal.
Key Aspects of the Slaking of Lime
- Reactants:
- Calcium Oxide (CaO): A highly reactive white solid produced by heating limestone (calcium carbonate).
- Water (H₂O): The solvent and reactant for hydration.
- Product:
- Calcium Hydroxide (Ca(OH)₂): Also known as slaked lime or hydrated lime.
- Energy Release: The reaction is vigorously exothermic, causing the mixture to heat up and, in some cases, boil. This heat release is due to the formation of stronger bonds in the product.
- Applications: This reaction is fundamental in various industrial and agricultural processes, as calcium hydroxide is a widely used chemical.
Properties and Uses of Calcium Hydroxide
Calcium hydroxide possesses several useful properties that lead to its extensive applications.
Properties of Calcium Hydroxide
| Property | Description |
|---|---|
| Appearance | White powder or colorless crystals |
| Solubility in Water | Sparingly soluble, forms limewater (solution) and milk of lime (suspension) |
| pH | Strongly alkaline (basic) solution |
| Reactivity | Reacts with acids to form salts and water, absorbs CO₂ from air |
| State | Solid at room temperature |
Common Uses of Calcium Hydroxide
- Agriculture: Used to neutralize acidic soils, improving their fertility (liming).
- Water Treatment: Flocculant in water purification, removing impurities, and adjusting pH.
- Construction:
- Key component in mortar, plaster, and cement.
- Used in whitewash for walls.
- Industrial Applications:
- In sugar refining to precipitate impurities.
- In the production of various chemicals, including bleaching powder.
- As a substitute for lye in chemical relaxers.
- Food Industry: Used in food processing, such as pickling and processing of corn (nixtamalization).
Understanding both the limited dissolution of calcium hydroxide in water and its significant formation reaction from calcium oxide provides a comprehensive view of its chemical behavior.
