Chemistry 9701/21 Oct Nov 2018 | Cambridge AS Level Past Papers With Mark Scheme

1. Iron Pyrite (FeS₂):
- Electronic configurations, oxidation numbers of sulfur in S₂²⁻.
- Reactions of impure iron pyrite and environmental consequences (sulfur dioxide).
- Roasting process and mass calculations for FeS₂ and gold impurity.

2. Nitrogen (N₂):
- Explanation of the inert nature of nitrogen and drawing its dot-and-cross diagram.
- Reactions of nitrogen and oxygen during lightning strikes, and the formation of nitric acid.

3. Nitrate Fertilizers:
- Environmental impact of uncontrolled nitrate fertilizer use on aquatic life.
- Reaction of calcium hydroxide with ammonium ion, and reactions involving ammonium nitrate and nitric acid.

4. Organic Chemistry (Trihalomethanes):
- Properties of CHCl₃, including high vapor pressure and enthalpy calculations.
- Catalysis (heterogeneous catalyst) and its application in the formation of CHClF₂.
- The environmental impact of CHClF₂ and its role in the greenhouse effect.

5. Polymer Chemistry:
- Formation of PTFE (polytetrafluoroethylene) from tetrafluoroethene.
- Reasons for PTFE’s use as a cooking pan coating and challenges in its disposal.

6. Glycolic Acid:
- Chemical reactions and mechanisms, including the reduction of glyoxylic acid to glycolic acid.
- Infrared spectroscopy interpretation, drawing the structures of glycolic acid derivatives.