Problem 1: One method to remove metals from water is to raise the pH and cause them to precipitate as their metal hydroxides. The pH of water was initially 6.8 and was then raised to 8.0. Is the dissolved cadmium concentration reduced to below 100 mg/L at the final pH? Ksp = 5.33x10-15 (HINT: the solid in precipitation / dissolution reactions = 1 when writing the equilibrium equation) Cd2+ + 2OH <-> Cd(OH)2(s)

Problem 2: At a wastewater-treatment plant FeCl3(s) is added to remove excess phosphate from the effluent. Assume that the reactions that occur are FeCl3(s) <-> Fe3+ + 3Cl- Fe3+ + PO43 <-> FePO4(s) The equilibrium constant for the second reaction is 1026.4. What concentration of Fe3+ would be needed to maintain the phosphate concentration below the limit of 1 mg P/L? Assume all P as PO43-. (HINT: use second reaction to write the solubility equilibrium)

Problem 3: A sample of water having a pH of 6.8 has the following concentration of ions. Determine the waters total hardness.

Ion	Concentration (mg/L)	Ion	Concentration (mg/L)
Ca2+	35	HCO3-	98
Mg2+	9	SO42-	70
Na+	13.2	Cl-	15
K+	10	Fe2+	2

Problem 4: How much oxygen can be dissolved in water from the atmosphere at 298.15K? The Henrys law constant for oxygen is 1.3 x 10-3 mol / L-atm. The percentage of O2 in air is 21%. Express your answer as mg / L. (MW = 32 g/mole)