The US Environmental Protection Agency (EPA) places limits on the quantities of toxic substances that may be discharged into the sewer system. Limits have been established for a variety of substances, including hexavalent chromium, which is limited to 0.50 mg/L. If an industry is discharging hexavalent chromium as potassium dichromate (K2Cr2O7), what is the maximum permissible molarity of that substance?

1).Determine the number of moles represented by the given massof each of the following substances:
a).23.68 g of lead iodine,PbI2
b).0.791 g of propane,C3H8
c).3.45x10^2 g of potassium dichromate,K2Cr2O7
d).14.32g of calcium phosphate,Ca3(PO4)2
e).4.92 g of copper sulfate pentahydrate,CuSO4 X 5H2O

2).Calculate the mass represented by the given number of moles ofthe following substance:
4.35 X 10^-6 mol of iron (III)oxide,Fe2O3

3).Calculate the mass percent made up by each element in thefollowing compound :
phosphoric acid, H3PO4

Some potassium dichromate (K₂Cr₂O₇), 2.335 g, is dissolved in enough water to make exactly 500.mL of solution. What is the molar concentration of the potassium dichromate? What are the molar concentrations of the K⁺ and Cr₂O₇^2– ions?