Chemistry 9701/35 Oct Nov 2020 | Cambridge AS Level Past Papers With Mark Scheme

1. Determining the Value of x in Sodium Thiosulfate Hydrate: The experiment investigates the value of x in the formula of hydrated sodium thiosulfate, Na2S2O3•xH2O, by preparing a solution and titrating it with iodine.
2. Titration of Sodium Thiosulfate: Using a titration with iodine to determine the number of moles of sodium thiosulfate, and subsequently calculating the relative formula mass and identifying x in Na2S2O3•xH2O.
3. Calculation of Percentage Error: Methods to calculate the maximum error in measuring the mass of sodium thiosulfate and the effect of experimental uncertainties on the final result.
4. Experimental Procedures and Improvements: Suggestions for improving the experimental setup to increase accuracy, such as adjusting titration techniques and ensuring proper handling of reagents.
5. Thermal Decomposition of Sodium Carbonate: Measuring the thermal decomposition of sodium thiosulfate and comparing the calculated relative formula mass with titration data.
6. Qualitative Tests for Anions and Cations: Identifying ions in unknown samples through various reactions such as those involving silver nitrate and sodium thiosulfate, and writing ionic equations for observed reactions.