Chemistry 9701/21 May June 2010 | Cambridge AS Level Past Papers With Mark Scheme

1. Chlorine and Bromine Physical States: Chlorine is a gas at room temperature due to weaker intermolecular forces compared to bromine, which has stronger van der Waals forces, making it a liquid at the same temperature.
2. Boiling Point Comparison of N₂ and CO: N₂ has a lower boiling point than CO because CO exhibits dipole-dipole interactions, while N₂ only has London dispersion forces.
3. Dot-and-Cross Diagrams for CO: Identification of co-ordinate bonds, covalent bonds, and lone pairs in a CO molecule using dot-and-cross diagrams.
4. Reactivity of Isoelectronic Molecules: Despite having the same number of electrons, CO and HCN are reactive due to the availability of lone pairs and polarity, while N₂ is inert due to its stable triple bond and lack of polarity.
5. Reaction of HCN with Ethanal: The reaction with ethanal forms an imine (Schiff base), and the reaction is a nucleophilic addition. The mechanism involves electron pair movement and bond formation.
6. Boltzmann Distribution at Higher Temperature: The Boltzmann distribution curve shifts to the right with increasing temperature, indicating that more molecules have energy greater than the activation energy at higher temperatures.
7. Activation Energy Definition: The activation energy is the minimum energy required for a reaction to occur, representing the energy barrier that must be overcome for reactants to convert into products.
8. Haber Process Conditions: The catalyst is iron, and the typical operating conditions are a temperature of around 450°C and a pressure of about 200 atmospheres.
9. Effect of Catalyst on Reaction Rate: A catalyst lowers the activation energy, providing an alternative reaction pathway with a lower energy barrier, which increases the reaction rate.
10. Reactions of NaOH with Organic Compounds: Reaction 1 requires heating because it involves a nucleophilic substitution, while reaction 2 is an acid-base neutralization, which occurs instantly at room temperature.
11. Periodic Table Element Properties: The identification of elements with specific properties, such as the largest cation, elements that float on water, and elements with specific reactivities.
12. Fluorides of Period 3 Elements: Ionic fluorides are likely formed by elements with low electronegativity, such as Na and Mg. SF₆ has an octahedral shape, and the non-existence of ClF₇ is due to the lack of orbital overlap to accommodate the bonding requirements in chlorine.
13. Organic Reaction Scheme: The reaction scheme starting from propene involves multiple steps with reagents like KMnO₄, NH₃, NaOH, and HBr to form various organic products.
14. Functional Groups in Organic Reactions: In the reaction between compounds B and E, an amide functional group is formed, typically carried out by heating with concentrated acid in a laboratory setting.
15. Isomerism Types: Structural isomerism occurs when compounds have the same molecular formula but different structural arrangements. Stereoisomerism can arise from features like double bonds or chiral centers.
16. Organic Acids from Fruit: Tartaric acid reacts with NaHCO₃ to form a salt, and citric acid does not show optical isomerism due to the presence of a plane of symmetry in its structure.
17. Empirical and Molecular Formula Calculation: The empirical formula of W is calculated based on its composition, and the molecular formula is determined using the molar mass. The number of carboxylic groups in W is deduced from titration data.