Is CaCl2 + (NH4)2CO3 → CaCO3 + 2NH4Cl a precipitation reaction?
The Correct Answer and Explanation is:
Yes, the reaction CaCl₂ + (NH₄)₂CO₃ → CaCO₃ + 2NH₄Cl is a precipitation reaction.
In a precipitation reaction, two aqueous solutions combine to form an insoluble solid called a precipitate. This reaction falls under the category of double displacement or metathesis reactions, where the positive ions (cations) and negative ions (anions) in the reactants switch places to form new products.
In this case:
- Calcium chloride (CaCl₂) and ammonium carbonate ((NH₄)₂CO₃) are both soluble salts. When dissolved in water, they dissociate into their respective ions:
- CaCl₂ → Ca²⁺ + 2Cl⁻
- (NH₄)₂CO₃ → 2NH₄⁺ + CO₃²⁻
When these ions are present together in solution, calcium ions (Ca²⁺) react with carbonate ions (CO₃²⁻) to form calcium carbonate (CaCO₃), which is insoluble in water and therefore precipitates out of the solution as a solid. The other ions, ammonium (NH₄⁺) and chloride (Cl⁻), remain in solution as ammonium chloride (NH₄Cl), a soluble salt.
So the net ionic equation for the reaction is:
Ca²⁺(aq) + CO₃²⁻(aq) → CaCO₃(s)
This clearly shows the formation of a solid from aqueous ions, confirming that this is indeed a precipitation reaction. The visible sign of this reaction would be the appearance of a white solid (calcium carbonate) in the solution.
Precipitation reactions are important in chemistry for separating ions from a solution or identifying substances based on the solids they form. In laboratory settings, they are often used for qualitative analysis or water purification processes. This reaction demonstrates classic characteristics of precipitation—aqueous reactants forming an insoluble product.
