A 250 mL aqueous solution contains 0.25 M sodium benzoate and 0.20 M benzoic acid…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 250 mL aqueous solution contains 0.25 M sodium benzoate and 0.20 M benzoic acid (pK_a = 4.20).
(a) Determine the initial pH of the solution before any reagent is added.
(b) A student introduces 0.0050 mol of HCl(g) (which dissolves completely) to the solution. Assuming the volume change is negligible, calculate the new pH.
(c) The same quantity of HCl(g) is bubbled into 250 mL of pure water at 25 °C. Compute the resulting pH of this unbuffered solution.
(d) Compare quantitatively the pH changes for the buffered versus unbuffered solutions. Explain, with reference to relevant chemical principles, why the difference in pH shift is observed.