2023 VS 6092 P2 MS Chemistry Prelim

1 Victoria School 2022 Secondary 4 Chemistry Prelim Answer Scheme + Markers’ Report Paper 1 1 2 3 4 5 6 7 8 9 10 B D C C C C B A A D 11 12 13 14 15 16 17 18 19 20 D D C A A D B D A D 21 22 23 24 25 26 27 28 29 30 B B D A C A C D D B 31 32 33 34 35 36 37 38 39 40 A D D D A D B A C C Paper 2 Section A Qn Suggested answers Mark A1a CO2 1 A1b K 1 A1c Ni 1 A1d Ca(OH)2 1 A1e K/Ni and Cl2 1 A1f SO2 1 A2ai They dissolve/ionise/dissociate in water to produce H+/hydrogen ions. 1 A2aii Add a 2 cm magnesium strip into 25.0 cm3 of 1 mol/dm3 of both acids. Measure the time taken for the strips to totally react away, T will take a shorter time / Measure volume of gas produced in 5 min, T will produce a larger volume / Measure time taken to collect 10 cm3 of gas, T will take a shorter time REJECT: collect total volume of gas as both will be equal if Mg is limiting. Max 1m: qualitatively determine that T produces a faster speed of reaction (more vigorous effervescence for T) 1 1 A2aiii Brown solution will turn colourless / decolourise. 1 A2bi H+ + OH- → H2O 1 A2bii pH 9.2 Accept range from 9.0 to 9.4 1 499

2 Qn Suggested answers Mark A2biii 13/14 pH 0/1 1m - both correct pHs 1m - 40 cm3 Reject: pH 2 for strong acid 2 A2ci T reacts with calcium carbonate to form an insoluble layer of calcium sulfate that coats on the carbonate, preventing further reaction. 1 A2cii amount of calcium carbonate = 1 100 = 0.0100 mol amount of acid used = 1.2 x 0.050 = 0.0600 mol since 2H+  Ca, calcium carbonate is the limiting agent. since Ca  CO2, volume of CO2 = 0.0100 x 24 = 0.240 dm3 1 1 1 A2d 1m – ester linkage 1m – displayed formula (only if ester linkage present) 2 A3ai Glutamic acid, sodium hydroxide and monosodium glutamate are all soluble in water (to form colourless solution). 1 A3aii 112 dm3 of sodium hydroxide solution. (must state but no mark) Glutamic acid is dibasic/2 mol of sodium hydroxide reacts with 1 mol of glutamic acid (to form a disubstituted salt) (11.20 cm3 will react with 25.0 cm3 aqueous sodium hydroxide to form a monosubstituted salt.) 1 1 A3bi copper(II) oxide/copper(II) hydroxide 1 A3bii Excess copper(II) carbonate can be removed by filtration but not glutamic acid. 1 A4a Total energy absorbed for bond breaking = 610 + 4(414) + 2(463) = 3192 kJ Total energy released from bond forming = 346 + 5(414) + 358 + 463 = 3237 kJ Total energy change = 3192 – 3237 = -45.0 kJ 1 1 1 40 volume of aqueous NaOH/cm3 500

3 Qn Suggested answers Mark A4b 1m – Ea(1) and curve 1m – Ea(2) and curve 1m – energy level and product with state symbol 1m – ΔH 4 A5ai 1 1 A5aii Catalyst / enzyme 1 A5bi Butanal C3H7CHO 1 1 A5bii C