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, Hydrogen ions gets reduced to form hydrogen gas at the cathode (potassium will not be discharged) while chloride ions (due to its high concentration) gets oxidised to form chlorine gas. The potassium and hydroxide ions will form potassium hydroxide which has a pH of more than 7, resulting in an increase in the pH of the electrolyte. 17 A At the copper anode, copper, which loses electrons more readily than the anions present, will undergo oxidation to form copper(II) ions. 18 B As the energy level of the products is higher than that of the reactants, this is an endothermic reaction. The activation energy, which is the minimum energy particles must possess before a reaction can proceed, can be found by subtracting R from P . 19 C Statement 1: The activation energy, Ea, is the minimum energy the colliding particles must have in order to react. The other 2 statements are true as thermal energy is taken in during an endothermic reaction and this leads to a decrease in T of the surrounding. Bonding making is an exothermic process as energy is given out. 20 A Increasing the pressure and temperature in the vessel increases the rate of reaction involving gases. 21 D Neutralisation is exothermic in nature and the enthalpy change is negative. 22 A Method 1 measures the volume of carbon dioxide gas collected through the displacement of water, method 2 measures the mass loss due to loss of carbon dioxide. There’s no measurement in a physical quantity in method 3 that allows the rate of reaction to be measured. 23 D Statements 3 and 4 confirm the acidic nature of dilute sulfuric acid as acids have pH less than 7 and react with copper(II) oxide. 24 C Non-metal oxides are usually acidic in nature. Carbon reacts with oxygen to form carbon dioxide which is acidic. 25 D The indicators turn yellow in solutions with pH more than 5. Only Z has pH more than 5. 26 A Copper(II) nitrate is a soluble salt which can be prepared by reacting excess base / carbonate with acid.

27 A Iron has been oxidised to form iron(II) while hydrogen in sulfuric acid has been reduced to form hydrogen gas. 28 B The melting point of halogens increases as molecular size increases. 29 C The group number in the Periodic Table is determined by the number of valence electrons while the period number is determined by the number of occupied shells. The elements are arranged according to increasing proton number. 30 B The charge on the silver ion is 1+. Silver ions undergo reduction to form silver, Ag while magnesium undergo oxidation to form Mg2+. 31 D In rust prevention, zinc forms a barrier between iron and the oxygen and water in the atmosphere. When a layer of zinc is scratched, it gets oxidised before iron does. When iron rusts, atoms of iron loses electrons to form ions. 32 D Oxygen which is formed during photosynthesis does not have an effect on global warming. 33 B A reduction in livestock farming reduces the production of methane and reduces the effect of climate change. Using low-sulfur fuel reduces the amount of sulfur dioxide which contributes to acid rain. 34 A Finely divided iron is used as catalyst in the Haber process. The addition of hydrogen to alkene produces alkane. 35 B Sugar cane is a renewable resource. Sugar cane undergoes photosynthesis in which carbon dioxide is utilised. 36 D Since there is only one carbon-carbon double bond in both molecules, they react with equal masses of bromine. 37 C Ethane reacts with chlorine in a step-wise substitution reaction in which the hydrogen atom in ethane is progressively replaced by a chlorine atom. 38 A Equation for combustion of hexan-3-ol: C6H13OH + 9O2 → 6CO2 + 7H2O 39 C Methyl propanoate can be formed from methanol and propanoic acid. The C−O must be found in methanol while the C=O must be found in the acid. 40 B The repeat unit of X is –[CH(CH3)CH(CH3)]– while Y must be a polyester as it is formed between a dicarboxylic acid and a diol.

Paper 2 1 (a)(i) CO 1 (ii) Al2O3 / PbO 1 (iii) CO / CO2 / SO2 / H2O 1 (iv) CaO / PbO 1 (v) CO2 / CaO / Na2O / SO2 1 (vi) CO2 1 (b) • fractional distillation • boiling points of both glucose and ethanol are different. 1 1 2 (a) particle number of particles electron 18 neutron 16 proton 15 1 (b) P needs 3 electrons to fulfill the noble gas configuration / octet structure. 1 (c)(i) Yes. It is an ionic compound with giant crystal / ionic lattice structure and strong electrostatic forces of attraction between oppositely charged ions. A lot of energy is required to overcome the strong electrostatic forces of attraction hence, calcium phosphate is expected to have high melting point. 1 1 (ii) Percentage by mass of phosphorus = 2x31/(3x40+2x31+8x16) x 100% = 20.0% 1 3 (a) 3MoO2 + 4Al → 2Al2O3 + 3Mo 1 (b)(i) element oxidation state in reactants oxidation state in products molybdenum +4