The reaction between potash alum (KAl(SO₄)₂·12H₂O) and sodium carbonate (Na₂CO₃) is a double displacement reaction that produces a precipitate. Here's a breakdown of what happens:

Reaction Equation:

2 KAl(SO₄)₂·12H₂O + 3 Na₂CO₃ → Al₂(CO₃)₃ (s) + 3 K₂SO₄ + 6 Na₂SO₄ + 24 H₂O

Explanation:

* Double Displacement: The positively charged ions (cations) and negatively charged ions (anions) of the reactants switch partners.

* Precipitate Formation: Aluminum carbonate (Al₂(CO₃)₃) is insoluble in water, meaning it doesn't dissolve readily. This causes it to form a solid precipitate that settles out of the solution.

* Other Products: Potassium sulfate (K₂SO₄) and sodium sulfate (Na₂SO₄) are soluble in water and remain dissolved.

* Water: The water molecules from the hydrated alum and the reaction itself are also present in the solution.

In Summary:

When potash alum reacts with sodium carbonate, a white precipitate of aluminum carbonate forms, along with soluble potassium sulfate and sodium sulfate. The reaction is essentially a process of exchanging ions between the two reactants, leading to the formation of a solid product.