GVBProblems Set 2 by fY7R4421

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									Chemistry 3100                       Winter 2011                              Dr. G. Van Biesen

                         Problem Set II: Acid-Base Chemistry
   1. The Ka of barbituric acid is 9.8 x 10-5.

   1a) Calculate the pH and fraction of dissociation of 0.010 M barbituric acid
       Answer: pH = 3.03;  = 9.4%

   1b) Calculate the pH and fraction of dissociation of 10-10 M barbituric acid
      Answer: pH = 7.00;  = 99.9%

              (This is Problem 8-13 in Harris 8th Edition)


   2. How many mL of 0.246 M HNO3 should be added to 213 mL of 0.00666 M 2,2’-
      bipyridine (pKa = 4.34) to give a pH of 4.19?
      Answer: 3.38 mL

              (This is Problem 8-38 in Harris 8th Edition)


   3. Calculate the pH of a solution prepared by mixing 0.0800 mol chloroacetic acid (pKa =
      2.865) and 0.0400 mol sodium chloroacetate in 1.00 L of water.

      3a) Assume that the formal concentrations of chloroacetic acid (HA) and chloroacetate
      (A-) are equal to their formal concentrations
      Answer: pH = 2.56

      3b) Show that the real values of [HA] and [A-] are slightly different from the formal
      concentrations, and calculate a more accurate pH
      Answer: pH = 2.61

      3c) What is the pH of a solution prepared by dissolving following compounds in a beaker
      with a total volume of 1.00 L: 0.180 mol chloroacetic acid, 0.020 mol sodium
      chloroacetate, 0.080 mol HNO3, and 0.080 mol Ca(OH)2 (assume Ca(OH)2 dissociates
      completely).
      Answer: pH = 2.86

              (This is Problem 8-40 in Harris 8th Edition)
Chemistry 3100                      Winter 2011                              Dr. G. Van Biesen

                         Problem Set II: Acid-Base Chemistry
   4a) How many mL of ammoniumhydroxide (with a molarity of NH3 of 14.8 M) have to be
      added to a solution of 5.345 g NH4Cl in water in order for the final solution, when diluted
      to 1.000 L, to have a pH of 9.00? pKa of ammonium is 9.24.
      Answer: 3.89 mL

   4b) What is the pH of this solution after addition of 3.00 mL of 10 M HCl?
     Answer: pH = 8.57

   4c) What is the pH of this solution after addition of 6.00 mL of 10 M HCl?
       Answer: pH = 2.60



   5. Consider a 0.0500 M solution of benzene-1,2,3-tricarboxylic acid: H3C9H3O6.
              Ka1 = 1.32 x 10‾3, Ka2 = 1.78 x 10‾5, Ka3 = 7.4 x 10‾8

   5a) Give the pH range where each species is predominant.

   5b) Calculate the pH of 0.0500 M H3C9H3O6 (aq).
      Answer: 2.13

   5c) Calculate the [HC9H3O62‾ ] in 0.0500 M H3C9H3O6 (aq) if the pH is adjusted to 5.00
       Answer: 0.032 M

   5d) Calculate the ratio between [H2C9H3O6‾] and [HC9H3O62‾] if the pH of the solution is
      3.00.
      Answer: 56:1


   6. Calculate the pH after the addition of 0.0 mL, 18.0 ml, 25.0 mL, 38.0 mL,
      50.0 mL and 65.0 ml of 0.200 M NaOH(aq) to 50.0 mL of 0.100 M malic acid.
      pK1 = 3.459 pK2 = 5.097
      Answer: 2.24, 3.87, 4.28, 5.13, 8.90, 12.42

   7. A solution was prepared from 10.0 mL of 0.100 M cacodylic acid (HA – Ka = 6.4 x 10-7)
    and 10.0 mL of 0.0800 M NaOH. To this mixture was added 1.00 mL of 1.27 x 10-6 M
    morphine (B – Kb = 1.6 x 10-6). What is the fraction of morphine present in the BH+ form?
    Answer: 96%
                            (This is Problem 9-34 in Harris 8th Edition)

								
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