Question

A water supply has been contaminated with an unknown mixture of toxic metal solutions leaking from a nearby factory. One way to treat the problem is to precipitate the metals from the water. Environmental chemists are considering using sodium carbonate and sodium sulfate for this purpose. Based on the solubility table, which compound would you recommend?

Answer 1

Answer is: sodium carbonate (Na₂CO₃).
Sodium carbonate is better because carbonate anion with metal cations form more insoluble salts (according to table below, six insoluble salts - with magnesium, calcium, barium, silver, zinc and lead cations) and sulfate anion with metal cations form only two insoluble salts (barium sulfate and lead(II) sulfate).