NYGH 2024 SIP Chemistry Prelim Key

2024 SIP Chemistry Prelim Key Paper 1 1 2 3 4 5 6 7 8 9 10 D A D C C D B A D C 11 12 13 14 15 16 17 18 19 20 A B C A B B A B C A 21 22 23 24 25 26 27 28 29 30 D A D C D A A B C B 31 32 33 34 35 36 37 38 39 40 D D B A B D C A C B Explanation No Ans Explanation 1 D When T decreases, particles have less KE and move more slowly from one another. 2 A Ethylamine has lower Mr of 45 as compared to hydrogen chloride with Mr of 36.5 and diffuses at a slower rate. Hence the white solid will be formed at A. 3 D Oxygen is an element, glucose C6H12O6 is a compound (fixed composition) and air (which has variable composition of components from which it’s made up) is a mixture. 4 C copper(II) sulfate and water can be separated by simple distillation(to obtain water) or crystallization (to obtain copper(II) sulfate); methanol and ethanol are separated by fractional distillation due to their different bp; methanol and ethanol can be separated by fractional distillation due to their different bp; sand and silver chloride cannot be separated by filtration as both are insoluble in water. 5 C The molecules that can be obtained are C2H335Cl3, C2H337Cl3, C2H335Cl237Cl, C2H335Cl37Cl2 6 D Magnesium reacts with dilute hydrochloric acid to form magnesium chloride (ionic compound) and hydrogen (molecules of element). Magnesium atom transfer 2 electrons, one to each chlorine atom. 7 B Particles that enable electrical conductivity are free, mobile ions and delocalised electrons. Copper is able to conduct electricity due it its ‘sea’ of delocalised electrons while graphite can conduct electricity as there is one valence electron per carbon atom that is not involved in bonding. 8 A The total number of electrons in the compound includes those which are not in the valence shells. Each bond in the diagram represents a pair of electrons. 9 D Zinc ions produces a white precipitate in both aq sodium hydroxide and ammonia which dissolves in excess. 10 C Only silver ions will form a white precipitate with chloride ions. 11 A Percentage composition of N in N2O = (14x2)/(14x2+16) x 100% = 63.6% Percentage composition of O in N2O = (16)/(14x2+16) x 100% = 36.4%

12 B No. of moles of calcium nitrate = 13.3/(40+2x14+6x16) = 0.08110 By comparing mole ratio, no. of moles of calcium oxide = 0.08110 mass of calcium oxide present = 0.081 x (40+16) = 4.54 g Percentage purity = 4.54/7 x 100% = 65.0% 13 C C3H8 + 5O2 → 3CO2 + 4H2O Initial 60 100 Used 20 100 Left / produced 40 0 60 80 (but it will cool to a liquid) Total volume of gas = 40 + 60 = 100 cm3 14 A Products of electrolysis: lead (grey) and bromine (reddish – brown) Reaction at cathode: Pb2+ reduced by gaining 2 e− to form Pb. Reaction at anode: Br- oxidised by losing 2 e− to form Br2. 15 B Magnesium and silver are the furthest from each other in the electrochemical series and hence, produces the highest voltage. 16 B For concentrated potassium chloride,