A student prepared a buffer solution by adding 0.0150 mol of a salt NaA\text{NaA}NaA to 150 cm3 of a 0.400 mol dm-3 solution of a weak acid HA\text{HA}HA and mixing thoroughly.
The student then added 5.00 × 10-3 mol of sodium hydroxide (NaOH\text{NaOH}NaOH) to the buffer solution. Calculate the pH\text{pH}pH of the buffer solution after adding the sodium hydroxide.
For the weak acid HA\text{HA}HA at 25∘C25^\circ\text{C}25∘C, the value of the acid dissociation constant is Ka=1.75×10−5 mol dm−3K_{\text{a}} = 1.75 \times 10^{-5}\text{ mol dm}^{-3}Ka=1.75×10−5 mol dm−3.
Give your answer to two decimal places.
Explain why diluting this buffer solution with water has almost no effect on its pH\text{pH}pH, using a mathematical expression to support your explanation.
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.