When calcium hydroxide reacts with sodium silicate, the primary outcome is the formation of insoluble calcium silicate, which causes the solution to harden rapidly upon exposure to air. This chemical interaction is a precipitation reaction, leading to a solid product.
The Chemical Transformation
The reaction involves two key inorganic compounds: calcium hydroxide and sodium silicate. According to the provided reference, the specific form of sodium silicate involved is Na2Si2O3, and the resulting calcium silicate is represented as CaO*SiO3.
- Calcium Hydroxide (Ca(OH)2): Also known as slaked lime, this is a white powder or colorless crystal. It is a base often used in various industrial applications, including water treatment and construction.
- Sodium Silicate (Na2Si2O3): Often referred to as water glass when in solution, sodium silicate compounds are versatile chemicals used in detergents, adhesives, and as binders. The specific form Na2Si2O3 reacts to form the insoluble product.
- Calcium Silicate (CaO*SiO3): This is the insoluble product of the reaction. Calcium silicates are fundamental components of cement and concrete, known for their binding and hardening properties. The notation CaO*SiO3 is a common way to represent calcium metasilicate (CaSiO3).
The chemical process can be summarized as the exchange of ions, where calcium ions from calcium hydroxide combine with silicate ions from sodium silicate to form the insoluble calcium silicate.
Summary of Reactants and Product
| Component | Chemical Formula (from reference) | State | Role in Reaction |
|---|---|---|---|
| Calcium Hydroxide | Ca(OH)2 | Reactant | Provides Ca²⁺ ions |
| Sodium Silicate | Na2Si2O3 | Reactant | Provides Si₂O₃²⁻ ions |
| Calcium Silicate | CaO*SiO3 | Product | Insoluble precipitate |
Why the Solution Hardens
The most notable consequence of this reaction is the immediate hardening of the solution when it is exposed to air. This phenomenon is attributed directly to the insolubility of the calcium silicate formed.
- Insolubility: Unlike the soluble sodium silicate, calcium silicate does not dissolve in water. As it forms, it precipitates out of the solution as a solid.
- Precipitation: This precipitation leads to the formation of a solid matrix within the solution.
- Rapid Hardening: The reference explicitly states that the solution "hardens right in the air!" This indicates a quick setting time, where the formation of the insoluble solid effectively transforms the liquid solution into a rigid, solid mass upon exposure to atmospheric conditions. This characteristic is often leveraged in applications requiring quick setting or binding properties.
This chemical transformation highlights a fundamental principle in chemistry where the formation of an insoluble product can significantly alter the physical state and properties of a solution, leading to practical applications in materials science and engineering.
