A 500.0 mL buffer solution is prepared by dissolving 0.25 mol NH₄Cl and 0.15 mol NH₃…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 500.0 mL buffer solution is prepared by dissolving 0.25 mol NH₄Cl and 0.15 mol NH₃ in water at 25 °C (pKₐ for NH₄⁺ = 9.25).
A student sequentially adds 0.020 mol HCl(g) (which dissolves completely) followed by 0.020 mol NaOH(s) to the buffer, allowing the solution to equilibrate after each addition.
(a) Calculate the pH of the original buffer before any additions.
(b) Calculate the pH after the addition of HCl.
(c) Calculate the pH after the subsequent addition of NaOH.
(d) Explain why the final pH is not equal to the initial pH even though equal amounts of strong acid and strong base were added.