Chemistry 9701/52 March 2020 | Cambridge AS Level Past Papers With Mark Scheme

1. Brass Composition Determination: A titration-based method to find copper percentage in brass, including steps for accurately weighing by difference, preparing solutions, and conducting a sodium thiosulfate titration with iodine.

2. Procedure for Accurate Weighing: A detailed method on weighing the brass powder by difference, ensuring the exact mass is recorded using a balance, with the appropriate results table.

3. Safety Procedures: Explanation for performing the reaction in a fume cupboard to safely handle nitric acid and released gases, ensuring proper lab safety.

4. Solution Preparation: Guidance on how to prepare solution B by dilution, including equipment used and volume specifications.

5. Titration Setup: Method for filling the burette with sodium thiosulfate and correct filling procedures, including ensuring no air bubbles are present.

6. Titration Calculations: Completing a titration table, calculating mean titres, determining percentage error in titres, and suggesting changes to minimize errors in titration measurements.

7. Moles and Copper Calculation: Calculation of moles of iodine produced, using it to calculate the moles of Cu2+ ions in solution A, leading to the determination of copper percentage in the sample.

8. Silver Ion Behavior: Explanation of why silver ions are removed in step 2 during the reaction due to their reaction with nitric acid.

9. Activation Energy Experiment: A series of steps designed to measure the activation energy of the reaction between manganate(VII) and ethanedioate ions, with focus on procedural details and data interpretation.

10. Data Interpretation: Completing a table to include log t and 1/T values, graphing the relationship between these variables, and using the graph to determine the gradient, leading to the activation energy calculation.

11. Graphing and Calculating Ea: Plotting data to derive the gradient of the line, using the gradient to calculate the activation energy of the reaction, with units specified.