An aqueous solution is prepared by dissolving 1920 mg of potassium hydrogen oxalate (KHC2O4\text{KHC}_2\text{O}_4KHC2O4) in water and making up to exactly 500 cm3 of solution. The measured pH\text{pH}pH of this solution at 298 K is 2.15.
Calculate the value of KaK_{\text{a}}Ka for the hydrogen oxalate ion (HC2O4−\text{HC}_2\text{O}_4^-HC2O4−) behaving as a weak acid in this solution. Give your answer to three significant figures. State the units of KaK_{\text{a}}Ka.
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.