Over the years, I have alternated this exercise with a glycine titration described elsewhere. The main purpose of this exercise is to review the concept of buffers and pKa. Students are given 75 mL of a 0.2 M solution of the base form of a buffer, which they will titrate with 0.5 M HCl. Any commonly-used buffers can be used; I use ethanolamine (pKa = 9.5), diethanolamine (pKa = 8.9), triethanolamine (pKa = 7.8), monohydrogen phosphate (effective pKa = 6.9) and morpholinoethanesulfonate (MES, titrated with an equivalent of NaOH). Using a pH meter, they titrate their solutions with 0.5 M HCl in 1-mL portions. From their tabulated and graphed data, they are asked to identify their buffer by its pKa and to indicate the pH range over which it would be an effective buffer.

Revised 2/21/08