### Richard A. Paselk

General Chemistry

Spring 2008

Exercise: pH and Buffer Problems

# pH and Buffer (Acid/Base Equilibrium) Problems

1. What is the pH of a solution of 0.033 M H2SO4?

2. What is the pH of a solution of 0.055 M barium hydroxide (it completely dissociates at this concentration).

3. What is the pH of a 0.15 M solution of boric acid, H3BO3. Ka = 6.0 x 10-10

4. Calculate the pH of a buffer made up by dissolving 0.150 moles sodium dihydrogenphosphate (NaH2PO4) and 0.100 moles of sodium hydrogenphosphate (Na2HPO4) in enough water to make 0.500 L of solution. Ka = 6.3 x 10-8 (FYI, this salt combination is commonly used in biological experiments, since it is a very effective buffer around pH 7.)

5. Calculate the pH of a buffer made up by dissolving 0.0230 moles ascorbic acid (H2C6H6O6) and 0.0440 moles of sodium ascorbate (NaHC6H6O6) in enough water to make 0.250 L of solution. pKa = 4.30.

6. What ratio of sodium dihydrogenphosphate (NaH2PO4) and sodium hydrogenphosphate (Na2HPO4) will give a buffer with a pH = 7.00? pKa = 7.20

7. Calculate the pH of the solution resulting when 0.250 L of 0.500 M acetic acid is mixed with 0.250 L of 0.350 M sodium hydroxide. pKa = 4.74.