NYJC Prelim H2 Chem 9729 P1 P2 P3 P4 Answers

Nanyang Junior College 2025 J2 H2 Chemistry Prelim Exam Answers 1 Paper 1 Answer Key Paper 2 Answers 1 (a) (i) [1] for all 3 plots and ensure that the plot at proton number 20 is lower than proton number 12. (ii) • The number of protons increase and nuclear charge increase. • Successive electrons are added to the same valence shell, shielding effect remains approximately constant. • Effective nuclear charge increases and electrostatic attraction between the nucleus and valence electron increases. • More energy is required to remove the valence electron (iii) Proton number 15: 1s2 2s2 2p6 3s2 3px1 3py1 3pz1 Proton number 16: 1s2 2s2 2p6 3s2 3px2 3py1 3pz1 [1] for both electronic configurations. Reject students who write 1s2 2s2 2p6 3s2 3px4 for proton number 16. Element with proton number 16, the valence electron to be removed is from the paired electrons in 3px orbital. Hence, it experiences inter-electronic repulsion arising from the two electrons occupying the same 3px orbital and requires less energy to remove. [1] 1 B 11 B 21 B 2 B 12 A 22 D 3 A 13 D 23 C 4 D 14 A 24 C 5 B 15 C 25 D 6 C 16 A 26 C 7 D 17 B 27 C 8 B 18 A 28 D 9 A 19 C 29 D 10 B 20 B 30 A

Nanyang Junior College 2025 J2 H2 Chemistry Prelim Exam Answers 2 (b) (i) [1] Copper has a giant metallic structure with strong metallic bonding (or electrostatic attraction) between copper ion and sea of delocalised electrons. The presence of sea of delocalised electrons acts as mobile charge carriers, hence making copper a good conductor of electricity. [1] (ii) • Both Na2O and MgO have giant ionic structure held together by strong ionic bonding (or electrostatic attraction) between positively charged metal cations and negatively charged oxide anions. • |LE|  |q+q−| r+ + r • Both Na2O and MgO have the same oxide anion, but Mg 2+ is doubly charged while Na+ is singly charged. • The ionic radius of Na+ > Mg2+. The magnitude of LE is larger for MgO than Na2O. • Ionic bonding of MgO is stronger than Na 2O. More energy is required to break the stronger ionic bonds between Mg 2+ and O2– in MgO than ionic bonds between Na + and O2– in Na2O. • Melting point of MgO is higher than Na 2O and hence able to withstand higher temperature in case of fire. 2 (a) (i) The order of reaction with respect to a given reacta nt is the power to which the concentration of that reactant is raised in the experimentally determined rate equation. [1] (ii) When [NaOH] decreases, gradient remains constant, hence rate of reaction is constant. Rate of reaction is independent of [NaOH], hence the reaction is zero order wrt [NaOH]. [1] When [CH3CHBrCH2CH3] = 0.25 mol dm−3 initial rate = 0.0048 / 30 = 1.60 x 10−4 mol dm−3 min−1 When [CH3CHBrCH2CH3] = 0.50 mol dm−3 initial rate = 0.0095 / 30 = 3.16 x 10−4 mol dm−3 min−1 When [CH3CHBrCH2CH3] doubles (0.50/0.25), the gradient doubles, showing that the rate of reac