Chemistry 9701/35 Oct Nov 2018 | Cambridge AS Level Past Papers With Mark Scheme

1. Sodium Carbonate Purity Determination by Titration: Measuring the purity of sodium carbonate by titrating with hydrochloric acid, calculating the moles of sodium carbonate reacted, and determining the mass of sodium carbonate in the sample.
2. Thermal Decomposition of Sodium Carbonate: Performing thermal decomposition of sodium hydrogencarbonate to calculate the percentage purity of sodium carbonate in a sample by measuring mass loss and analyzing decomposition products.
3. Energy Calculation in Reactions: Using temperature changes from reactions to calculate the energy released, applying the enthalpy change equation to find the mass of sodium carbonate used.
4. Experimental Accuracy and Assumptions: Discussing assumptions made during experiments, such as the behavior of impurities, and explaining the impact of these assumptions on the calculated values of the enthalpy change.
5. Comparison of Methods for Purity Measurement: Evaluating which method (titration or thermal decomposition) provides a more accurate result for determining sodium carbonate purity, and justifying the choice based on practical considerations.
6. Effect of Impurity on Enthalpy Change: Explaining how the presence of hydrated sodium carbonate instead of anhydrous sodium carbonate affects the experimental enthalpy change calculation.