Chemistry 9701/13 May June 2010 | Cambridge AS Level Past Papers With Mark Scheme

1. Ideal Gas Behavior: Helium closely approaches ideal behavior at room temperature and pressure due to its small atomic size and non-polar nature.
2. Ionization Energies: The order of ionization energies for radon, francium, and radium follows Rn > Ra > Fr, based on their positions in the periodic table.
3. Electron Configuration: The element with three unpaired electrons is likely to have the proton number of 15, which corresponds to phosphorus (P).
4. Enthalpy of Formation: The standard enthalpy of formation for iodine trichloride is calculated as –176 kJ/mol, based on the provided enthalpy data.
5. Bond Energy Reactions: The order of enthalpy changes for given reactions is P → Q → R → S, indicating the energy involved in bond breaking and forming for each reaction.
6. Gas Volume Calculation: The mass of gas that occupies 3 dm³ at standard temperature and pressure is 5.6 g of N₂ gas.
7. Oxidation States in NH₄NO₃ Decomposition: The oxidation state of nitrogen changes from +4 in NH₄NO₃ to –6 in N₂O, confirming the redox process.
8. Haber Process and Temperature: Increasing temperature shifts the equilibrium toward the backward reaction, reducing ammonia yield.
9. Element Identification: The metal reacting with chlorine to form XCl₂ is calcium (Ca), based on the reaction mass data.
10. Acid and Base Dissociation: The conclusion that X is a strong acid is correct (P), but the extent of dissociation in X and Y is better explained by Q.
11. Sulfuric Acid and Sodium Chloride: Sulfuric acid behaves as both an acid and an oxidizing agent when reacting with sodium chloride.
12. Pool Water Treatment: Acidifying the pool water helps maintain a higher concentration of HOCl by shifting equilibrium.
13. Precipitation Rate: The faster formation of precipitate with 0.05 mol dm–3 Na₂S₂O₃ is due to more frequent collisions between reactant particles.
14. Possible Identity of X: The salt X in reactions with HNO₃ and AgNO₃ could be potassium iodide (KI).
15. Ammonia Yield vs. Pressure: At higher temperatures, increasing pressure enhances ammonia yield in the Haber process, as shown in graph C.
16. Properties of Phosphorus and Sulfur: Phosphorus has an oxide that forms a strong acid, and sulfur lacks paired 3p electrons.
17. Element Identification in Period 3: X, Y, Z are identified as silicon, phosphorus, and sulfur, based on ionization energies and melting points.
18. Group II Elements: The stability of Group II element carbonates decreases with increasing atomic number.
19. Combustion Reaction: Magnesium requires the least oxygen for complete combustion, confirming its reactivity.
20. Non-Flammable Gas: Oxygen is the non-flammable gas among the listed options.
21. Reaction with Alcohols: Sodium reacts differently with alcohols based on their structure.
22. Propanone Reaction: The product of propanone refluxed with NaBH₄ is propan-2-ol.
23. Free Radical Substitution: The free radical X• can be formed in 3 different ways in the reaction with 2,2-dimethylbutane.
24. Reactivity with Reagents: Acidified potassium dichromate reacts similarly with both butanone and butanal, resulting in the oxidation of both.
25. Hydrolysis of Acyl Chloride: Hydrolysis of CH₃CO₂C₃H₇ produces propan-1-ol and acetic acid.
26. Isomerism in Alkenes: 2-methylpropan-2-ol exhibits both cis-trans and optical isomerism.
27. Recycling of PVC: PVC is removed from incineration waste because its combustion produces harmful products.
28. Polymerization of 1,1-Dichloroethene: The polymerization of 1,1-dichloroethene produces a substance with a high melting point and dense structure.
29. Molecular Structure: The most likely molecular structure of Y is 2,2-dimethylpropane, as it undergoes hydrolysis in aqueous alkali.
30. Dehydration of Alcohols: 2-methylpropan-2-ol undergoes dehydration to form three alkenes, suggesting its structure.