When sodium sulfate (Na₂SO₄) and calcium chloride (CaCl₂) are mixed in aqueous solutions, they undergo a double displacement reaction, resulting in the formation of calcium sulfate (CaSO₄) and sodium chloride (NaCl). This type of reaction can be fully understood by examining both the molecular equation and its complete ionic equation.
The Molecular Equation
First, let’s write the balanced molecular equation for the reaction:
Na2SO4(aq)+CaCl2(aq)→CaSO4(s)+2NaCl(aq)
In this equation:
- Na₂SO₄ is sodium sulfate, which dissociates into sodium ions (Na⁺) and sulfate ions (SO₄²⁻) when dissolved in water.
- CaCl₂ is calcium chloride, which dissociates into calcium ions (Ca²⁺) and chloride ions (Cl⁻) in solution.
- CaSO₄ is calcium sulfate, a solid precipitate that forms because it has low solubility in water.
- NaCl is sodium chloride, which remains dissolved in water as Na⁺ and Cl⁻ ions.
The Complete Ionic Equation
To write the complete ionic equation, we need to break down the strong electrolytes into their respective ions. In the case of Na₂SO₄, CaCl₂, and NaCl, these compounds dissociate completely in water. The precipitate, CaSO₄, does not dissociate because it is insoluble. Here’s the complete ionic equation:
2Na+(aq)+SO42−(aq)+Ca2+(aq)+2Cl−(aq)→CaSO4(s)+2Na+(aq)+2Cl−(aq)
Explanation of the Complete Ionic Equation
- Ions in Solution:
- Sodium sulfate (Na₂SO₄) dissociates into 2 Na⁺ ions and 1 SO₄²⁻ ion.
- Calcium chloride (CaCl₂) dissociates into Ca²⁺ ions and 2 Cl⁻ ions.
- Sodium chloride (NaCl) dissociates into Na⁺ and Cl⁻ ions in the aqueous phase.
- Precipitation of Calcium Sulfate (CaSO₄):
- When Ca²⁺ and SO₄²⁻ ions come together in solution, they form calcium sulfate (CaSO₄), which precipitates out because it has low solubility in water.
- Spectator Ions:
- The Na⁺ and Cl⁻ ions do not participate in the formation of the precipitate. These are referred to as spectator ions, meaning they remain in the aqueous phase unchanged during the reaction.
The Net Ionic Equation
The next step is to eliminate the spectator ions to obtain the net ionic equation. This focuses on the species that actually participate in the reaction. By removing the 2 Na⁺ and 2 Cl⁻ ions from both sides, we’re left with:
Ca2+(aq)+SO42−(aq)→CaSO4(s)
This is the net ionic equation, which highlights the essential chemical change: the formation of the solid calcium sulfate precipitate from its ions in solution.
Conclusion
The complete ionic equation for the reaction between sodium sulfate (Na₂SO₄) and calcium chloride (CaCl₂) is:
2Na+(aq)+SO42−(aq)+Ca2+(aq)+2Cl−(aq)→CaSO4(s)+2Na+(aq)+2Cl−(aq
This equation shows how the ions interact in solution, and how calcium sulfate precipitates out, leaving the spectator ions Na⁺ and Cl⁻ in the aqueous phase. Understanding ionic equations is crucial in predicting the outcomes of reactions in aqueous solutions and for grasping the role of solubility in chemical processes.