CEE 350 - Korshin - Winter 2012 - Quiz 2(1)

CEE 350 - Korshin - Winter 2012 - Quiz 2(1) - solid phase...

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Class CEE 350 Pop-up quiz #2 Name ______________________ Determine the concentration of dissolved oxygen (in mg/L as O 2) in wa ter in equilibrium with oxygen in the air at 25ºC. The partial pressure of oxygen is 0.21 Atm, and the Henry constant K H of oxygen at this temperature is 0.00126 mol·L - 1 ·Atm -1 . The atomic weight of oxygen is 16 g/mol. The molar concentration of dissolved oxygen can simply be determined as >@ ± ² L mol P K O O H / 10 65 . 2 00126 . 0 21 . 0 4 2 2 ³ ´ u The concentration of oxygen in mg/L as O 2 can now be determined as >@ ±² ± ² ± ² L mg L mol mol mg O MW C O O / 5 . 8 / 10 65 . 2 / 32000 4 2 2 2 ´ u ³ Sketch the behavior of the speciation factors of carbonic acid ( D H2CO3 , D HCO3- , D CO32- ) as a function of pH. The pK values of carbonic acid are 6.3 and 10.3. 0.00 0.25 0.50 0.75 1.00 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 pH Contribuion of species carbonic acid bicarbonate carbonate pK 1 =6.3
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Unformatted text preview: solid phase CaCO 3 . The total concentration of carbonate in the solution is 210-4 mo/L and the pH is 10.3. The solubility product of calcite is 10-8.3 . The atomic weight of calcium is 40 g/mol. The pH given in the problem is equal to pK2 of carbonic acid. Therefore, the concentration of carbonate ion CO 3 2- at this pH is one half of the total carbonate concentration. That is, it is equal to TOTCO 3 /2=10-3 mol/L. As a result, we can determine the molar concentration of calcium in the system via its solubility product: > @ > @ L mol CO K Ca sp / 10 5 10 10 10 5 3 .. 4 4 3 . 8 2 3 2 The concentration of calcium in mg/L can now be determined as > @ L mg L mol mol mg Ca AW C Ca Ca / . 2 / 10 5 / 40000 5 2 2 2 u...
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