Final answer:
None of the salts CuCl2, Na3PO4, or CsBr are expected to form a precipitate in water. Sodium sulfate, however, will precipitate the barium ion Ba2+ as barium sulfate (BaSO4), which is insoluble in water.
Step-by-step explanation:
To determine which salt forms a precipitate in water, we need to consider the solubility rules. Among the options given, such as CuCl2, Na3PO4, and CsBr, none of these salts are expected to form a precipitate as all are soluble in water. In the case of barium ions, to find a solution that would precipitate Ba2+, we look for a compound that forms an insoluble salt with barium. According to solubility rules, sodium sulfate (Na2SO4) will form an insoluble salt, as barium sulfate (BaSO4) is not soluble in water. Therefore, the expected precipitate when sodium sulfate is added to a solution containing Ba2+ is BaSO4. The balanced chemical equation for the reaction leading to the formation of the precipitate is:
Ba2+(aq) + SO42-(aq) → BaSO4(s)