Answer
Because a precipitate formed with Na2SO4, the possible cations are Ba2+, Pb2+, Hg22+, and Ca2+ (from the solubility rules). Because no precipitate formed with KCl, Pb2+ and Hg22+ cannot be present. Because both Ba2+ and Ca2+ form soluble chlorides and soluble hydroxides, both these cations could be present. Therefore, the cations could be Ba2+ and Ca2+ (by the solubility rules in Table 4.1). For students who do a more rigorous study of solubility, Sr2+ could also be a possible cation (it forms an insoluble sulfate salt, whereas the chloride and hydroxide salts of strontium are soluble).
Work Step by Step
Because a precipitate formed with Na2SO4, the possible cations are Ba2+, Pb2+, Hg22+, and Ca2+ (from the solubility rules). Because no precipitate formed with KCl, Pb2+ and Hg22+ cannot be present. Because both Ba2+ and Ca2+ form soluble chlorides and soluble hydroxides, both these cations could be present. Therefore, the cations could be Ba2+ and Ca2+ (by the solubility rules in Table 4.1). For students who do a more rigorous study of solubility, Sr2+ could also be a possible cation (it forms an insoluble sulfate salt, whereas the chloride and hydroxide salts of strontium are soluble).
