During municipal water treatment, alum (which contains aluminium sulfate) is added to raw water to act as a coagulant. The hydrated aluminium ions, [Al(H2O)6]3+[\text{Al}(\text{H}_2\text{O})_6]^{3+}[Al(H2O)6]3+, react with dissolved carbonate ions, CO32−\text{CO}_3^{2-}CO32−, representing the natural alkalinity of the water. This reaction produces a gelatinous precipitate that helps flocculate and settle out impurities, accompanied by the evolution of a gas.
What are the formulas of the precipitate and the gas formed?
Al(H2O)3(OH)3\text{Al}(\text{H}_2\text{O})_3(\text{OH})_3Al(H2O)3(OH)3 and CO2\text{CO}_2CO2
Al2(CO3)3\text{Al}_2(\text{CO}_3)_3Al2(CO3)3 and CO2\text{CO}_2CO2
Al(H2O)3(OH)3\text{Al}(\text{H}_2\text{O})_3(\text{OH})_3Al(H2O)3(OH)3 and SO2\text{SO}_2SO2
Al2(CO3)3\text{Al}_2(\text{CO}_3)_3Al2(CO3)3 and SO2\text{SO}_2SO2
