Understanding the Reaction:
* Aluminum Sulfate (Al₂(SO₄)₃): This is a soluble salt that dissociates in water to form aluminum ions (Al³⁺) and sulfate ions (SO₄²⁻).
* Ammonia (NH₃): This is a weak base that dissolves in water to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻).
The Reaction:
The reaction is a double displacement reaction followed by hydrolysis. Here's a breakdown:
1. Initial Reaction:
Al₂(SO₄)₃(aq) + 6 NH₃(aq) + 6 H₂O(l) → 2 Al(OH)₃(s) + 3 (NH₄)₂SO₄(aq)
2. Explanation:
* Aluminum ions (Al³⁺) react with hydroxide ions (OH⁻) from ammonia to form aluminum hydroxide (Al(OH)₃), which is a white, gelatinous precipitate.
* Ammonium ions (NH₄⁺) combine with sulfate ions (SO₄²⁻) to form ammonium sulfate ((NH₄)₂SO₄), which remains dissolved in the solution.
Important Notes:
* Hydrolysis: The aluminum hydroxide precipitate is actually a product of hydrolysis. When Al³⁺ ions come in contact with water, they react with water molecules to form Al(OH)₃ and H⁺ ions. This reaction is favored by the presence of ammonia, which consumes H⁺ ions, driving the hydrolysis forward.
* pH Dependence: The reaction is pH-dependent. At a lower pH (more acidic), the reaction is less likely to occur. At a higher pH (more basic), the reaction is more likely to occur.
Overall:
The reaction between aluminum sulfate and ammonia results in the formation of a white aluminum hydroxide precipitate and ammonium sulfate in solution. The reaction is a complex process involving double displacement and hydrolysis.
