Acid-base titrationsEdexcel International A Level Chemistry: Flashcards

Exam questions on Acid-base titrations

1. In a titration, 0.100 mol dm⁻³ sodium hydroxide is run from a burette into 25.0 cm³ of hydrochloric acid of unknown concentration in a conical flask. Methyl orange and phenolphthalein are both available as indicators.
   The end point is reached when 21.40 cm³ of sodium hydroxide has been added. Calculate the concentration of the hydrochloric acid in mol dm⁻³.2 marks
2. A student prepares a standard solution of ethanedioic acid dihydrate, H₂C₂O₄·2H₂O (M = 126.1 g mol⁻¹). She weighs 1.58 g of the solid in a beaker, dissolves it in deionised water and makes the solution up to 250 cm³ in a volumetric flask.
   Explain why the student adds the last of the water drop by drop until the bottom of the meniscus is on the graduation mark, and then inverts the flask several times.2 marks
3. The student uses the standard ethanedioic acid solution, of concentration 0.0501 mol dm⁻³, to find the concentration of a solution of sodium hydroxide. She fills a burette with the acid and titrates 25.0 cm³ portions of the sodium hydroxide solution, using phenolphthalein. The equation is H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O. The mean of her concordant titres is 22.60 cm³.
   Describe how the student should carry out one titration so that the end point is found accurately.3 marks