Chemistry 9701/23 Oct Nov 2018 | Cambridge AS Level Past Papers With Mark Scheme

1. Iron Pyrite (FeS₂) Chemistry:
- Understanding the electronic configuration of Fe²⁺.
- Determining the oxidation number of sulfur in S₂²⁻.
- Describing metallic bonding in gold.
- Roasting of impure iron pyrite to extract gold, including calculations for mass of FeS₂ and percentage purity of gold.
- Environmental impacts of sulfur dioxide, such as acid rain formation.

2. Nitrogen and Nitrogen Oxides:
- Explaining the inertness of nitrogen and drawing a dot-and-cross diagram for N₂.
- The reaction of N₂ and O₂ during lightning strikes, leading to the formation of nitrogen monoxide (NO).
- Reactions of NO to form nitric acid (HNO₃) and its environmental impact.
- Discussing the effects of uncontrolled nitrate fertilizer use on water systems.

3. Ammonium Compounds and Fertilizers:
- Role of calcium hydroxide in soil neutralization.
- The reaction of calcium hydroxide with ammonium ions to release ammonia gas.
- Observations in the reaction between calcium carbonate and ammonium nitrate.
- Thermal decomposition of calcium nitrate.

4. Organic Chemistry: Halogenated Methanes and Reactions:
- Understanding vapour pressure and reactivity of CHCl₃ (chloroform).
- Enthalpy change calculation for the formation of CHClF₂ and its role in the greenhouse effect.
- The environmental consequences of using CHClF₂, such as its contribution to global warming.

5. Polymer Chemistry and PTFE:
- Polymerization of tetrafluoroethylene (PTFE) and its applications, including use as a non-stick coating.
- Environmental issues with the disposal of PTFE.
- The structure of PTFE and its molecular properties.

6. Glycolic Acid Synthesis and Reactions:
- Observations when glycolic acid reacts with Na₂CO₃, 2,4-DNPH, and acidified Cr₂O₇²⁻.
- The synthesis of glycolic acid from various precursors, including formaldehyde and cyanide.
- Reaction mechanisms such as SN2 and the role of NaBH₄ in the reduction of glyoxylic acid to glycolic acid.
- Infrared spectroscopy analysis of glycolic acid and its heated product, providing insights into functional group changes.