Pollution and hard water treatment by precipitation

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Intros
Lessons
  1. What is 'pollution' and hard water?
  2. Using precipitation to clean water.
  3. Worked calculation: Using Ksp and equilibrium to treat water.
  4. Hard water.
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Examples
Lessons
  1. Use the Ksp expression to calculate concentrations of aqueous ions in treating water pollution.

    A sample of industrial waste water has a Pb2+ concentration of 7.9*10-4 M, and 'acceptable levels' of lead ions in water have been stated as a maximum of 7.25*10-10 M.

    What amount of OH- ions need to be added to precipitate lead ions, so that [Pb2+] drops to the acceptable level at most? The Ksp for Pb(OH)2 is 1.43*10-20 M.1
    1. Use the Ksp expression to calculate concentrations of aqueous ions in treating water pollution.

      A sample of industrial waste water has a Pb2+ concentration of 6.5*10-3 M, and 'acceptable levels' of lead ions in water have been stated as a maximum of 7.25*10-10 M.

      What amount of CO32- ions need to be added to precipitate lead ions, so that [Pb2+] drops to the acceptable level at most? The Ksp for PbCO3 is 7.4*10-14 M.1

      1 Reference for solubility constant data: http://www4.ncsu.edu/~franzen/public_html/CH201/data/Solubility_Product_Constants.pdf