Chemistry 9701/35 Oct Nov 2016 | Cambridge AS Level Past Papers With Mark Scheme

1. Determination of Percentage Purity of Calcium Carbonate:
- Method 1: Measuring the volume of CO₂ gas produced when calcium carbonate reacts with excess hydrochloric acid. The volume of gas helps determine the amount of pure calcium carbonate in the sample.
- Method 2: Using titration to determine the amount of unreacted hydrochloric acid after the reaction with marble chips, allowing calculation of the purity of calcium carbonate.

2. Titration Process:
- Using sodium hydroxide to titrate the remaining hydrochloric acid in flask X after the reaction. The data from the titrations are used to calculate the amount of hydrochloric acid left, which is then used to determine the amount of calcium carbonate in the sample.

3. Calculations:
- Moles of CO₂ and HCl are calculated based on the volumes of gases collected and titration data. These values are then used to determine the mass and percentage purity of calcium carbonate.

4. Qualitative Analysis:
- Tests for various cations and anions, involving heating solids, dissolving them in acid, and adding reagents like sodium hydroxide or ammonia to identify the ions present. Observations such as color changes, precipitates, and solubility are recorded for analysis.

5. Practical Techniques:
- Methods for accurately conducting titrations, collecting gases, and handling chemicals like hydrochloric acid, sodium hydroxide, and sulfuric acid.