Chemistry 9701/13 Oct Nov 2019 | Cambridge AS Level Past Papers With Mark Scheme

1. Synthesis of Yttrium Barium Copper Oxide (YBa2Cu3O7): Calculating the minimum required masses of BaCO3 and CuO needed to react with Y2O3 to maintain a molar ratio of 1:2:3 and obtaining the highest yield of YBa2Cu3O7 after cooling.
2. Determining the Proportion of Cu3+ Ions: Describing the steps to determine the amount of Cu3+ ions in YBa2Cu3O7, including reactions with HBr and sodium citrate, followed by titration with S2O3²⁻.
3. Electrochemical Analysis: Using electrochemical data to explain the necessity of neutralizing the mixture and removing Cu2+ ions via complex formation with citrate anions.
4. Titration for Cu3+ Ion Concentration: Establishing the relationship between moles of Cu3+ and I2(aq) from titration data to calculate the moles of Cu3+ in the sample.
5. Preparation of Sodium Citrate Solution: Calculating the mass of sodium citrate needed to prepare a 1.0 mol/dm³ citrate ion solution and the preparation method for accurate solution concentration.
6. Titration Method Improvement: Identifying issues with the titration method, such as inconsistent titration results, and suggesting improvements.
7. Experiment to Test Effect of Moles on Temperature Change: Proposing an experiment to test how varying the moles of trichloromethane influences the temperature change when mixed with propanone.
8. Viscosity and Mean Molecular Mass of Poly(phenylethene): Using a capillary viscometer to determine the viscosity and mean molecular mass of poly(phenylethene) by plotting and analyzing the data.
9. Improving Accuracy in Viscometer Experiments: Suggesting methods to ensure accurate measurements of viscosity, and predicting the effect of temperature changes on measurement results.
10. Polymer Structure Determination: Calculating the number of repeat units in poly(phenylethene) based on viscosity data and explaining the relationship between polymer structure and molecular mass.