Washing soda (sodium carbonate decahydrate – Na₂CO₃·10H₂O) is obtained from sodium chloride through the Solvay process. In this method, ammonia (NH₃) reacts with carbon dioxide (CO₂) to form ammonium bicarbonate (NH₄HCO₃). This ammonium bicarbonate then reacts with sodium chloride (NaCl) in a solution to produce sodium bicarbonate (NaHCO₃) and ammonium chloride (NH₄Cl). Sodium bicarbonate is separated and then heated, resulting in the release of water and carbon dioxide, leaving behind anhydrous sodium carbonate (soda ash). By crystallizing soda ash from a solution, washing soda is obtained when it incorporates ten water molecules, forming Na₂CO₃·10H₂O.