St_Gabriels_2024_Prelims_4NA_Sc(Chem)_P3n4_MS

2024 ‘N’ Level Preliminary Examination Marking Scheme Sc(Chemistry) 5015/3 & 4 Sec 4 Normal (Academic) Paper 3 1 2 3 4 5 6 7 8 9 10 D B B C A B A C D C 11 12 13 14 15 16 17 18 19 20 C A D B D B A C B D Paper 4 Section A 1 (a) K and N 1 (b) M 1 (c) No. J contains an unknown dye. 1 (d) Change the solvent (water) to ethanol. 1 2 (a) (i) Chlorine Mass number Number of protons in nucleus Number of neutrons in nucleus 35Cl 35 17 18 37Cl 37 17 20 (ii) Both are chlorine atoms with (same number) 17 protons but different number of neutrons. 35Cl has 18 neutrons and 37Cl has 20 neutrons. 1 (b)(i) NaCl 1 (ii) Correct charge and number of electrons around sodium ion – 1m Correct charge and number of electrons around chloride ion – 1m 2 (iii) Ionic Bonding 1 3 (a) Test tube E F G H Mass of nails after 1 week/g 4.9 4.2 4.4 4.0 1 + ¯

(b) In test tube H, there is no oxygen in the boiled water and the layer of oil prevents oxygen from the air from entering. 1 (c) There will be brown rust on the surface of the nails. 1 (d) Paint the nails or coat the nails with zinc, grease, etc. 1 4 (a) Copper(II) oxide / Copper(II) hydroxide / Copper(II) carbonate 1 (b) Measuring cylinder 1 (c) Step 2: Filtration Step 3: Crystallisation 1 1 (d) To obtain a saturated solution/ To prevent thermal decomposition of the crystals 1 (e) (i) Mr = 108 + 35.5 = 143.5 1 (e) (ii) No of mols = 50 143 5. = 0.0348 1 Section B 5 (a) Propene 1 (b) X The difference in relative molecular mass of W and X is more than 14(CH2) The number of hydrogen atoms in X is more than twice the number of carbon atoms. X does not follow the general formula of the other five hydrocarbons 1 1 (c) CnH2n 1 (d) Correct rectangle block with Mr = 126 1 (e) Carbon dioxide and water. 1 (f) Test: Add (Bubble) aqueous bromine separately to the saturated and unsaturated hydrocarbons. Results: Unsaturated hydrocarbon will decolourise reddish brown aqueous bromine to colourless solution. Aqueous bromine remains as reddish brown in saturated hydrocarbons. 1 1 6 (a) (i) Fractional distillation 1 (ii) Bitumen It is collected near to the bottle of the column 1 1 (b) (i) Cracking / Catalytic cracking 1 (ii) C8H18 1 any one

(c) (i) 1 (ii) Poly(ethene) is non-biodegradable, it can not be broken down by bacteria or other living organism in the soil. • Harmful gases may produce when poly(ethene) is burnt • Burying poly(ethene) in landfills can lead to increasing amount of built-up waste. • When thrown into the sea can harm marine animals 1 1 Any one