Yuan Ching Prelim Ans

Yuan Ching Secondary School Preliminary Examination 2024 Secondary Four Express Chemistry (Revised) 6092 Paper 1 Answer Key 1 D 21 A 2 D 22 D 3 C 23 B 4 C 24 C 5 C 25 A 6 C 26 B 7 A 27 A 8 D 28 D 9 D 29 D 10 D 30 A 11 C 31 C 12 A 32 D 13 C 33 D 14 C 34 C 15 D 35 C 16 D 36 D 17 C 37 A 18 B 38 D 19 B 39 D 20 B 40 D

Chemistry (Revised) 6092 Paper 2 Marking Scheme Section A (70 marks) S/No. Answers Marks 1 (a) C 1 (b) A 1 (c) B 1 (d) D 1 2 (a) Methane, it has the smallest / lowest relative molecular mass than the rest of the gases 1 (b) Temperature affects the kinetic energy of the particles. At higher temperatures, particles move faster and further apart (ORA) Keeping the temperature at a constant ensures that particles have the same average kinetic energy. 1 1 (c) 132s 1 (d) Ammonia is soluble in water. Hence it will back into the way of the graduated cylinder. 1 3 (a) Y is the weak acid Reference to Universal indicator colour to pH (i.e orange indicator a higher pH than red) Reference to rate of gas produced in 10s (i.e. rate of reaction is slower as it produces less hydrogen in 10s compared to X) ALLOW: infer lower concentration of hydrogen ions is lower in acid Y as compared to acid X. [1m only] MUST quote data (“use information from table”) 1 1 1 (b) no. of mol of NaOH produced = 221000 x 0.100 = 0.0022 mol by mol ratio, H2A : NaOH 1 : 2 0.011: 0.0022 Concentration of tartaric acid = 0.0011 / 0.025 = 0.044 mol/ dm3 1 1 1

4 (a) halogen Colour and state at room temperature and pressure chlorine Yellow-green gas bromine Red-brown liquid iodine Purple-grey solid [1m] correct states [1m] correct colours [MAX 1m]: 2 correct states & colours 2 (b)(i) Chlorine is more reactive than bromine in Group 17, chlorine displaces bromide from aqueous sodium bromide solution, causing aqueous bromine to form which is brown in colour. 1 (b)(ii) When a jet of iodine gas is aimed at a filter paper soaked in a solution of sodium bromide. There is no displacement reaction as iodine is less reactive than bromine. Filter paper turns brown slowly as iodine gas dissolved in the aqueous solution to give a brown solution When a jet of bromine gas is aimed at a filter paper soaked in a solution of sodium iodide. Filter paper turns brown as iodine is less reactive than bromine hence bromine displaces iodine from sodium iodide, causing aqueous iodine to form which is brown in colour. [1m]: brown colour for iodine in aq. state in both cases [1m]: explain no displacement reaction for iodine gas with bromide salt [1m]: displacement reaction takes place for bromine gas with iodide salt 3 (c) Chlorine has a strong tendency to gain electrons from other elements to for