2024 Prelims RVHS H2 Chem P3 (Ans)

River Valley High School 9729/03/PRELIMS/24 2024 Preliminary Examination [Turn over River Valley High School 2024 JC 2 H2 Chemistry 9729 Prelim Paper 3 Suggested Solutions 1 (a) (i) Dynamic equilibrium refers to a reversible process at equilibrium in a closed system, in which the rate of forward reaction is equal to the rate of backward reaction, where there is no net change in concentration of reactants and products. (ii) 𝐾𝑐 = [𝐻2][𝐼2] [𝐻𝐼]2 (iii) Initial amount of HI = 15.4 = 0.1204 mol127.9 [HI]initial = 30.1204 = 0.06020 mol dm2.00 − [HI]change = 30.06020 0.34 = 0.02047 mol dm − 2HI(g) = H2(g) + I2(g) []initial/ mol dm−3 0.06020 0 0 []change/ mol dm−3 − 0.02047 + 0.010235 + 0.010235 []eqm/ mol dm−3 0.03973 0.010235 0.010235 ( ) ( ) 2 c 2 0.010235 K = = 0.0664 (to 3 s.f.) 0.03973

2 River Valley High School 9729/03/PRELIMS/24 2024 Preliminary Examination (iv) The KC value will increase. [✓] Position of equilibrium will shift right [✓] to favour the forward endothermic reaction [✓] to absorb the some of the heat. [✓]. (Hence the concentration of hydrogen and iodine will increase while the concentration of hydrogen iodide will decrease.) (b) Benzylamine is the most basic because the electron-donating benzyl group (-CH2C6H5) makes the lone pair of electrons on the N atom the most available for donation/protonation. Phenylamine is the less basic than benzylamine because the lone pair of electrons on the N atom delocalised into the the benzene ring due to the overlap of the p-orbital of the N atom with the -electron cloud of benzene. 3-aminobenzonitrile is the least basic because the presence of the additional electron withdrawing nitrile (CN) increases delocalisation of the lone pair of electrons on the N atom into the benz ene ring. This causes the lone pair of electrons to be least available for donation/protonation.

3 River Valley High School 9729/03/PRELIMS/24 2024 Preliminary Examination [Turn over (c) (i) (ii) Electrophilic substitution Fe + 3/2 Cl2 → FeCl3 FeCl3 + Cl2 → FeCl4− + Cl+ [✓]

4 River Valley High School 9729/03/PRELIMS/24 2024 Preliminary Examination (d) (i) Hc = mc T n − Hc = (0.600 1000)(4.18)(40.0 25.0) 3.0078.0 −− Hc = 1978.12 = 978 kJ mol (to 3 s.f.)−−− (ii) Copper is a good conductor of heat and will - maximise heat transfer to the water. - allow more efficient transfer of heat. Any logical answer that points to maximising transfer of heat to water Copper will allow the calorimeter to withstand high pressure of the oxygen pump in.

5 River Valley High School 9729/03/PRELIMS/24 2024 Preliminary Examination [Turn over (iii) The apparent value obtained is less exothermic. [✓] The layer of black solid is soot/ carbon [✓] which suggest that incomplete combustion [✓] of benzene took place. 2 (a) (i) Na2