OCR A Level Chemistry A (H432) Chemistry B (H433) PAG 2: Acid-base titration Exam Questions and Mark Scheme

OCR A Level Chemistry A (H432) Chemistry B (H433) PAG 2: Acid-base titration Exam Questions and Mark SchemeThe equation for the reaction of aqueous phosphoric(V) acid, H3PO4, with aqueous sodium hydroxide, NaOH(aq) is shown below. H3PO4(aq) + 3NaOH(aq) → Na3PO4(aq) + 3H2O(l) 25.0 cm3 of a 0.200 mol dm−3 H3PO4(aq) is titrated with 0.600 mol dm−3 NaOH(aq). Which statement is correct? A. The end point occurs when 25.00 cm3 of NaOH(aq) has been added. B. The end point occurs when 75.00 cm3 of NaOH(aq) has been added. C. After titration the final solution contains 0.0150 mol of Na3PO4. D. After titration the final solution contains 0.0150 mol of H2O. Your answer [1] 2. A student carries out a titration. Sodium hydroxide solution is transferred to a conical flask using a pipette. Methyl orange indicator is added to the flask. Hydrochloric acid is added from a burette until the indicator changes colour. Which of the following would lead to the titre being larger than it should be? A. Rinsing the conical flask with water before adding the sodium hydroxide solution. B. Rinsing the burette with water before filling it with hydrochloric acid. C. Rinsing the pipette with water before filling it with sodium hydroxide solution. D. Adding extra drops of indicator. Your answer [1] 3. A student prepares a standard solution and carries out a titration. Which of the following would result in a titre that is larger than it should be? 1: Water is added to completely fill the volumetric flask, rather than to the graduation line. 2: The conical flask is washed out with water before carrying out each titration. 3: The pipette is washed out with water before carrying out each titration. A. 1, 2 and 3 B. Only 1 and 2 C. Only 2 and 3 D. Only 1