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Southern Methodist University School of Engineering and Applied Science SMU SSH 8321 SMU ME 5315

Southern Methodist University School of Engineering and Applied Science SMU SSH 8321 SMU ME 5315 NTU HW 741-N Treatment Technology I - Physical and Chemical Methods February 15, 2000 Dr. Roger Dickey tape problems: vthelp@seas.smu.edu. Stoichiometry -

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Southern Methodist University School of Engineering and Applied Science SMU SSH 8321 SMU ME 5315

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  1. Southern Methodist University School of Engineering and Applied Science SMU SSH 8321 SMU ME 5315 NTU HW 741-N Treatment Technology I - Physical and Chemical Methods February 15, 2000 Dr. Roger Dickey tape problems: vthelp@seas.smu.edu

  2. Stoichiometry - Consider a familiar acid-base reaction in aqueous solution: Hydrochloric Acid (Muriatic Acid) Sodium Hydroxide (Caustic Soda) Sodium Chloride (Table Salt) Water 1 unit 1 gm-mole 1 unit 1 gm-mole 1 unit 1 gm-mole 1 unit 1 gm-mole gm-mole => 6.02 x 1023 atoms, molecules, or formula units Avagadro’s Number

  3. (i) Molecular Weight, MW, (or Formula Weight) gm-Atomic Weight  the weight in grams of 1.0 gm-mole (i.e., 6.02 x 1023 atoms) of the element, which is numerically equivalent to the atomic weight (in atomic weight units) from the periodic table. gm-Molecular Weight  sum of the gm-Atomic Weights of the component atoms.

  4. In environmental work, it is common practice to deal exclusively with gm-moles (instead of lb-moles, or other similar units, which are comprised of a different number of atoms or molecules) and gm-molecular weights. As such, the terms mole and molecular weight will be used as abbreviated notation for gm-mole and gm-molecular weight, respectively.

  5. Example Compute the molecular weights of each substance in the previous acid-base reaction: NaCl:

  6. H2O:

  7. NaOH:

  8. HCl:

  9. Notice that a balanced chemical equation is another way of stating the Law of Conservation of Mass: 1 mole x 36.5 gm/mole 36.5 gm HCl 1 mole x 40.0 gm/mole 40.0 gm NaOH 1 mole x 58.5 gm/mole 58.5 gm NaCl 1 mole x 18.0 gm/mole 18.0 gm H2O 76.5 gm reactants  76.5 gm products

  10. (ii) Equivalent Weight, EW, where, n = number of equivalents per mole n is an integer whose value equals: (a) the number of H+ ions a substance “gives up” or “accepts” in a chemical reaction, (b) the number of electrons a substance “gives up” or “accepts” in a chemical reaction. (c) ion charge

  11. In any chemical reaction between two substances, 1.0 equivalent (eq.) of one substance always reacts with exactly 1.0 eq. of the other to yield exactly 1.0 eq. of product. This can sometimes simplify calculations. Consider a second common acid-base reaction: Sodium Sulfate (Salt Cake) Sulfuric Acid 1 mole x 98.1 gm/mole 98.1 gm H2SO4 2 mole x 40.0 gm/mole 80.0 gm NaOH 1 mole x 142.1 gm/mole 142.1 gm H2SO4 2 mole x 18.0 gm/mole 36.0 gm H2O 178.1 gm reactants  178.1 gm products

  12. EW H2SO4: 2 H+ to “give up”  n = 2 eq./mole

  13. EW NaOH: 1 OH- can “accept” 1 H+  n = 1 eq/mole

  14. Notice that H2SO4 and NaOH react in the following weight ratio:

  15. Similarly, in terms of equivalents,

  16. Other convenient units include - millimole, mmole = 10-3 mole milliequivalent, meq = 10-3 eq

  17. Concentrations - Molarity and Normality 1.0 Molar Solution  one mole of a substance dissolved in enough water to yield 1.0 liter of solution 1.0 M For example,

  18. 1 Normal Solution  one equivalent of a substance dissolved in enough water to yield 1.0 liter of solution 1N For example,

  19. Concentrations - Equivalence to Calcium Carbonate (CaCO3) Commonly used when dealing with acidity, alkalinity, and hardness in water and wastewater. Hardness Concentration  total concentration of divalent metallic cations Cations  (+) ions Anions  (-) ions

  20. Ca2+ and Mg2+ are the two principal hardness cations in natural waters (others are Fe2+, Mn2+, Sr2+) Hardness is reported as “mg/l as CaCO3” equivalent. 2+ ion charge, n = 2 eq/mole

  21. Examples - (1) Compute the MW and EW of CaCO3, Ca2+, and Mg2+, (2) Compute the hardness (mg/l as CaCO3) due to Ca2+ and Mg2+ for a water sample that contains 30.0 mg/l Ca2+ and 12.2 mg/l Mg2+

  22. Acidity  the capacity of a solution to neutralize bases Alkalinity  the capacity of a solution to neutralize acids

  23. Solids Classification - Total Dissolved Solids, TDS  material in a liquid that will pass through a 0.45  glass fiber filter Total Suspended Solids, TSS  material in a liquid that will not pass through a 0.45  glass fiber filter Total Solids, TS  all material dissolved and/or suspended in the liquid. TS = TDS + TSS

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