2025 AMKSS Prelim P2 MS

1 ANG MO KIO SECONDARY SCHOOLPRELIMINARY EXAMINATION 2025SECONDARY FOUR EXPRESSCHEMISTRY [6092]ANSWER SCHEMEPaper 2 Section A: Compulsory Structured Questions [70 Marks]1aP and S11bQ 11cP3U2 11d S 1Total42aCovalent bonding.Bonding between non-metal elements phosphorus and oxygen is covalent in nature.112bP4O6 1(R): P2O3 / O6P42cLiquid X is not able to conduct electricity.X has a simple molecular structure / is a simple molecule and does not have mobile ions or electrons to act as charge carriers to conduct electricity.112dpH of solution Y is less than pH 7. Substance X is acidic oxide as it is a non-metal oxide and will dissolve in / react with water to form an acidic solution.11Total73aBond breaking energy for 4 moles of C-F = 4 x 495 kJ/mol 2

2 = 1980 kJ Bond breaking energy for 2 moles of C-Cl = 2 x 339 kJ/mol = 678 kJ Bond breaking energy for 2 moles of C-H = 2 x 413 kJ/mol = 826 kJ Total bond breaking energy = 1980 + 678 + 826 = 3484 kJ (correct working = 1; correct ans = 1)3bBond forming energy for 4 moles of C-F = 4 x 495 kJ/mol = 1980 kJ Bond forming energy for 1 mole of C=C is 610 kJ Bond forming energy for 2 moles of H-Cl = 2 x 431 kJ/mol = 862 kJ Total bond forming energy = 1980 + 610 + 862 = 3452 kJ (correct working = 1; correct ans = 1)23c∆ H of the reaction = 3484 kJ – 3452 kJ = + 32 kJ1Allow for ecf3dFluorine is more reactive than chlorine. Therefore, the covalent bond formed between C – F is stronger than between C – Cl. Hence, it needs more energy to break the C – F bond compared to C – Cl bond.1Total64a2 NaN3  2 Na + 3 N2 14bMr of NaN3 = 23 + 3(14) = 65Number of moles of NaN3 used = 120 ÷ 65 = 1.84615 mol [1m]Mole ratio of NaN3 : N2 = 2 : 3 = 1.84615 : 2.76923Number of moles of N2 produced = 2.76923 mol [1m]Volume of N2 produced = 2.76923 × 24 dm3 = 66.46154 = 66.5 dm3 [1m]34ci10 Na + 2 KNO3  5 Na2O + K2O + N2 14ciiSodium is a very reactive metal which reacts violently with water and oxygen in air. 14dMethod: titration1

3 Reagents formulae: KOH / K2CO3 and HNO3 1Total85aNaOH and (NH4)2SO4 15bHNO3 and Zn15cCu(NO3)2 and Na2CO3 15dCu(NO3)2 and Zn15eKI and Ag(NO3)2 1Total56aPotassium chloride is an ionic compound.In the solid state, the oppositely charged ions in potassium iodi