CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Acetic acid, CH₃COOH, has pK_a = 4.76 at 25 °C. A biochemical laboratory prepares a series of acetic acid/acetate buffers to test the pH sensitivity of an enzyme.
(1) Calculate the ratio [CH₃COO⁻]/[CH₃COOH] required to prepare a buffer at pH 5.76. Show all work and include the appropriate number of significant figures.
(2) Calculate the ratio [CH₃COO⁻]/[CH₃COOH] required to prepare a buffer at pH 3.76. Show all work.
(3) Determine the pH at which the solution will be exactly 25 % deprotonated, that is, where [CH₃COO⁻] = 0.25 [CH₃COOH]. Provide complete calculations.
(4) Explain, without additional calculations, how your answers to parts (a)–(c) illustrate the buffering capability of the acetic acid/acetate system near its pK_a value.