1. The problem statement, all variables and given/known data Barium chloride is a toxic compound used in waste water treatment and many manufacturing processes. A 20 mL solution of 0.200 M Na2SO4 is added to a 10.0 mL water sample containing an unknown concentration of BaCl2 that was concentrated by 100 fold after being taken from a waste water treatment plant. After filtration of the solution, 0.7800g of the insoluble BaSO4(s) is obtained. Provide a balanced chemical equation and determine the concentration of the Ba2+ from the sample taken at the waste water treatment plant. 3. The attempt at a solution BaCl2(aq) + Na2SO4 [tex]\rightarrow[/tex] BaSO4(s) + 2NaCl Using dilution equation: C1V1=C2V2 C1(0.01)=(0.2)(0.02) C1=0.4M = [BaCl2] After Barium chloride is concentrated to a 100 fold which means the solution decreased volume. So 0.4M x 100 = 40M BUT, this solution isnt re-reacted with sodium sulfate therefore the 100x concentrated part doesn't matter in the problem. nBaSO4 = 0.78g / 233.3896 g/mol = 0.00334 mol BaSO4 [BaSO4] = [Ba2+] What I don't understand is why do I need to consider the 100x problem when i am given the mass of the precipitate and therefore just calculate how much barium ions I have ??? The 0.78g is fixed because thats what the experimentalists got. If the concentration of barium chloride is changed to 40M and then used to calculate the amount of Barium sulfate what does 0.78 grams measured from filtration matter then?