Two students prepare equal volumes of two aqueous solutions intended to buffer around…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Two students prepare equal volumes of two aqueous solutions intended to buffer around the pKa of acetic acid (4.74).
• Buffer A is made 0.20 M in CH₃COOH and 0.20 M in CH₃COO⁻(aq).
• Buffer B is made 1.00 M in CH₃COOH and 1.00 M in CH₃COO⁻(aq).
Assume both solutions have identical temperature and volume.
Strong acid challenge: 0.010 mol of HCl(g) is bubbled into each 1.0 L sample of buffer.
All solutions remain dilute and activity effects are negligible.
(1) Identify which buffer experiences the smaller change in pH after the addition of HCl(aq). Justify your answer with a comparison of the quantitative changes occurring in the conjugate pair for each buffer.
(2) Describe, at the particulate level, how the relative abundances of CH₃COOH and CH₃COO⁻ particles differ between the two buffers both before and after the acid addition, and explain how these differences account for the pH response you predicted in part (a).