Chemistry 9701/51 May June 2019 | Cambridge AS Level Past Papers With Mark Scheme

1. Synthesis of Yttrium Barium Copper Oxide (YBa2Cu3O7): Calculating the minimum masses of BaCO3 and CuO needed to react with Y2O3 for proper stoichiometric balance, ensuring the correct Y:Ba:Cu molar ratio of 1:2:3.
2. Electrochemical Analysis of Manganese Ions: Performing titrations to investigate the charge of manganese ions, including calculations of electrode potentials and the use of the Nernst equation.
3. Preparing Manganese Solutions: Detailed instructions for preparing diluted solutions of Mnz+(aq) using volumetric flasks and performing the experiment at various concentrations to measure electrode potential.
4. Graphical Data Interpretation: Plotting data to investigate the relationship between manganese ion concentration and electrode potential, and identifying anomalous results.
5. Determining the Standard Electrode Potential of Manganese: Using the Nernst equation and experimental data to calculate the standard electrode potential for manganese.
6. Determining the Charge of Manganese Ions: Using the calculated electrode potential and gradient of the graph to determine the charge (z) of the manganese ion.
7. Investigating the Effect of Temperature on Manganese Ion Behavior: Understanding how concentration changes affect the electrode potential and why the value becomes more negative.
8. Preparation of Propanone from Propan-2-ol: Calculating the mass of potassium dichromate needed for oxidation and preparing propanone using the given chemical reactions and apparatus.
9. Distillation Method for Separating Propanone: Explaining how distillation is used to separate propanone from the reaction mixture and discussing the necessity of using a water bath for refluxing.
10. Purification of Propanone: Identifying methods to remove sulfuric acid impurities from propanone and suggesting appropriate reagents.
11. Titration of Propanone with 2,4-DNPH: Understanding the procedure for confirming the identity of propanone by producing and isolating the 2,4-DNPH derivative.
12. Calculating Percentage Yield: Calculating the percentage yield of 2,4-DNPH derivative, considering theoretical and experimental data.
13. Improving Experimental Accuracy: Discussing why achieving 100% yield is not feasible in organic synthesis reactions and suggesting factors that may affect yield.