Arkansas State University Department of Chemistry and Physics

1. Calculate the pH of a buffer solution made from equal amounts of 0.30 M hydrofluoric acid and 0.70 M sodium fluoride.  K_a = 7.1 x 10^-4 [H⁺] = 3.04 x 10^-4; pH = 3.52

2. Calculate the pH of a buffer solution made from 0.30 M hydrofluoric acid and 0.70 M sodium fluoride after the addition of 0.08 mol of NaOH to 1 L of this solution.  Assume no change in volume. K_a = 7.1 x 10^-4    [H⁺] = 2.00 x 10^-4; pH = 3.70

3. Calculate the pH of a 0.08 M NaOH solution.  Compare to the pH found in problem 2.
pOH = 1.10; pH = 12.90

4.  What would be the buffer range for an acid if its K_a = 7.1 x 10^-4 ?
pK_a = 3.15; buffer range 2.15 to 4.15

5. Calculate the pH of a buffer solution made from 0.30 M hydrofluoric acid and 0.70 M sodium fluoride after the addition of 0.04 mol of HCl to 1 L of this solution.  Assume no change in volume. K_a = 7.1 x 10^-4   [H⁺] = 3.66 x 10^-4; pH = 3.44

6.  Calculate the pH of a 0.04 M HCl solution.  Compare to the pH found in problem 5.
pH = 1.40