A buffer solution is prepared by dissolving 0.095 mol0.095\text{ mol}0.095 mol of sodium benzoate (C6H5COONa\text{C}_6\text{H}_5\text{COONa}C6H5COONa) in 500 cm3500\text{ cm}^3500 cm3 of 0.150 mol dm−30.150\text{ mol dm}^{-3}0.150 mol dm−3 benzoic acid (C6H5COOH\text{C}_6\text{H}_5\text{COOH}C6H5COOH) solution at 25 ∘C25\text{ }^\circ\text{C}25 ∘C.
A sample of 20.0 cm320.0\text{ cm}^320.0 cm3 of 1.25 mol dm−31.25\text{ mol dm}^{-3}1.25 mol dm−3 nitric acid is added to this buffer solution.
Calculate the pH of the solution formed. Give your answer to 2 decimal places.
For benzoic acid, Ka=6.30×10−5 mol dm−3K_{\text{a}} = 6.30 \times 10^{-5}\text{ mol dm}^{-3}Ka=6.30×10−5 mol dm−3 at 25 ∘C25\text{ }^\circ\text{C}25 ∘C.
77 exam-style questions on AQA A Level Chemistry Acids and bases (A-level only), covering Brønsted–Lowry acid–base equilibria in aqueous solution (A-level only), Definition and determination of pH (A-level only), The ionic product of water, $K_w$ (A-level only), Weak acids and bases $K_a$ for weak acids (A-level only), pH curves, titrations and indicators (A-level only), and Buffer action (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.