Humboldt State University ® Department of Chemistry

Richard A. Paselk

	Introductory Chemistry	Fall 2005
Exercises: pH, Buffers etc.	© R. Paselk 2005
	Worked Examples
	Use Back Button to Return to Exercises

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

ANSWER

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

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

ANSWER

Example 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. K_a = 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.)

Both equilibrium and Henderson-Hasselbalch approaches are presented in the answer.

 

ANSWER

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

ANSWER

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

ANSWER

Example 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. pK_a = 4.74.

ANSWER

© R A Paselk

Last modified 23 June 2006