# 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?

(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

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

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).

(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.

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

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

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).

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

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

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?