The concentration of Pb2* in a sample of wastewater is to be determined by using gravimetric analysis. To a 100.0-mL sample of the wastewater is added an excess of sodium sulfide, forming the insoluble lead (II) sulfide (239.266 g/mol) according to the balanced equation given below. The solid lead (II) sulfide is dried, and its mass is measured to be 0.7086 g. What was the concentration of Pb2* in the original wastewater sample? Pb2"(aq) + Na2S(aq) PbS(s) + 2Na*(aq) >