2025 Montfort 6092 Chem P1 P2 PRELIM MS

2025 Montfort Secondary School S4 G3 Chem Prelim Answer KeyPAPER 1Q1Q2Q3Q4Q5DDBACQ6Q7Q8Q9Q10CDABAQ11Q12Q13Q14Q15CDDDAQ16Q17Q18Q19Q20CDDAAQ21Q22Q23Q24Q25BCDBCQ26Q27Q28Q29Q30ACBACQ31Q32Q33Q34Q35BDCCBQ36Q37Q38Q39Q40CBDDC

PAPER 2QANSWERMarkREMARK1aiC 11aiiA 11aiiiD 11aivG 11avC 11aviG 11bbonding pair of electrons between Cl and H 6 non-bonding electrons on chlorine atom and no extra electrons on the H atom(s) (1)12aAl4C3 + 12H2O → 4Al(OH)3 + 3CH4 formula for aluminium hydroxide as product (1) balanced equation (1)22bicontains only carbon and hydrogencontains single bonds only22biiAny two from: HCl (1) CH3Cl (1) CH2Cl2 (1) CHCl3 (1) CCl4 (1)22cibond breaking endothermic AND bond making exothermic / energy absorbed to break bonds in CH4 & O2 AND energy released on making bonds in CO2 & H2O (1) more energy released than absorbed (1)22cii M1 products to right of reactants AND reactant level above product level (1) M2 enthalpy change shown as downward arrow AND labelled as enthalpy change or  H (1) M3 activation energy drawn to maximum of energy hump with an upward arrow AND labelled (1) 3

3aiRate doubles as concentration doubles (or reverse argument) (1)13aiiParticles closer together / more particles in a given volume (or reverse argument) (1)Higher frequency of effective collision / more effective collisions per second (or reverse argument) (1)23aiiiIncreasing temperature increases rate (no marks)Particles move faster / particles have greater kinetic energy (1)Number of particles with energy greater than the activation energy is increased / higher frequency of effective collisions / more effectivecollisions per second (1)23biBurning fossil fuels / burning named fossil fuel / volcanoes (1)13biiIt is reformed / it is not used up / it is unchanged at the end of the reaction (1)14aianode (on left) and cathode (on right) correctly labelled (1)test tubes / measuring cylinders over each electrode with open ends dipping into the electrolyte (1)24aiipositive electrode: chlorine / Cl2 (1)negative electrode: hydrogen / H2 (1)24aiiiplatinum (no marks)inert / unreactive14bCl2 + 2NaI → I2 + 2NaCl (1)chlorine has displaced iodine in sodium iodide/ chlorine has taken the place of iodine in sodium iodide (1)25a3MoO2 + 4Al → 2Al2O3 + 3Mo (1)15bielementoxidation state in reactantsoxidation state in productsmolybdenum+40 (1 for correct row) aluminium0+3 (1 for correct row)25biimolybdenum(IV) oxide has been reduced as the oxidation state of molybdenum has decreased from +4 in MoO2 to 0 in Mo. (1)aluminium has been oxidised as the oxidation state has increased from 0 in Al to +3 in Al2O3. (1) Since oxidation and reduction occur simultaneously, this is a redox reaction. (no mark) 25cmolybdenum is less reactive (no mark)as it has been displaced from its oxide / molybdenum(IV) oxide has 1

been reduced by alumnium (1)5dimetallic bonding (1)structure drawn to show cations in a ‘sea’ of delocalised electrons. (1) 25diistronger electrostatic forces of attraction (1) due to higher number of electrons and protons present in Mo.16afertiliserformulaammonium nitrateNH4NO3 (1)sodium phosphateNa3PO4calcium nitrate (1)Ca(NO3)2potassium sulfateK2SO4 26biH+ + OH¯  H2O (1) 16bii N H C O % by mass 46.7 6.7 20 100 – (46.7+6.7+20) = 26.6 (1) no. of moles / mol (1) 46.71446.714 = 3.33571 6.716.71 = 6.7 20122012 = 1.66667 26.61626.616 = 1.6625 simplest ratio 3.335711.66253.335711.6625 = 2.01 6.71.66256.71.6625 = 4.03 1.666671.66251.666671.6625 = 1.00 1.66251.66251.66251.6625 =1.00 empirical formula N2H4CO (1)3 6cfarmer 2 is correct. (no marks)the nitrate ions from calcium nitrate provides the nitrogen content for healthy plant growth. (1)ammonium nitrate will react with calcium hydroxide to form ammonia gas (1) ;which will escape from the soil and causes a loss in the nitrogen content (1) required for healthy plant growth37aat 150 °C, 60 % of ammonia is formed. at 400 °C, 20 % of ammonia is formed. / any correct evidence data from Fig. 7.1 (1)as the temperature increases, the percentage of ammonia formed decreases. (1)27bat high temperature, the ammonia decomposes to form hydrogen and nitrogen. (1)17c (1)

7dwhen the pressure of gaseous reactants increases, there are more reacting particles per unit volume. (1)this increases the frequency of collision and hence increases the frequency of effective collision (1) between the reacting particles and thus, the rate of reaction increases. (1)37eithere will be unreacted or more or excess nitrogen monoxide released into the atmosphere together with less nitrogen and water vapour/steam produced (1)17eiiNO will react with air/oxygen to form NO2 which reacts with moisture and air (or water and oxygen) to form nitric acid (1)which reacts/dissolves in water; to form acid rain which corrodes limestone buildings/kills aquatic life (1) OWTTE; 28aihas a pungent smell (1)18aiiwhen hydrogen sulfide is combusted, it produces sulfur dioxide and sulfuric acid; which will corrode the metal machinery parts. (1)hydrogen sulfide is toxic (1)28benvironmental: (any three)if cow dung is not used, the cow dung will also degrade naturally to release methane which is a greenhouse gas; converting cow dung into biomethane to be used as biofuel instead of letting it degrade naturally cuts down greenhouse gases by 4%. this is because methane has a much greater global-warming power than carbon dioxide; conserves use of the limited/non-renewable fossil fuels/crude oil or the fertiliser made on the farm can reduce the synthetic fertilisers made from fossil fuels/ crude oil; 5

economical: (any two) cow dung is produced and/or collected directly on the farm or on-site and biodigester is on-site so farmers save on transportation costs and/or time; (reject easy to use) also cuts costs on using fossil fuels/crude oil for electricity; biomethane is a biofuel with high performance and high purity; the fertiliser produced from the biodigester can be readily used by farmers, saving costs from purchasing synthetic fertilisers;8cicarbon or hydrogen or carbon monoxide 18ciiiron(III) oxide is a solid product which can be collected more easily for recycling than the gaseous (or escaped) product, carbon dioxide, produced from the burning fossil fuels, which easily escapes into the atmosphere. 19athey have the (any 1 for 1 mark) • same general formula of CnH2n+2COO where n is ≥2 • same functional group of COO• Mr between successive members differ by 14 / molecular formula between successive members differ by a −CH229bthe melting point increases then decreases (no clear trend) (1) but the boiling point increases as the molecular size / Mr increases (1) 29cThe melting point is below 25 °C and (1)the boiling point is above 25 °C (1)OR25 °C is between (1) its melting and boiling point (1)29di (1)correct structural formula of organic acid(1)correct structural formula of compound Y29diino. of moles of acid = 1.20 g / 60 = 0.02 molno. of moles of methyl ethanoate = 0.02 mol (1)mass of methyl ethanoate = 0.02 x 74 = 1.48 g (1)2

10ai 110aii2C3H6 + 9O2 → 6CO2 + 6H2Ono. of moles of propene = (4.2x1000)/42 = 100 molvolume of carbon dioxide produced = 3 x 100 x 24 = 7200 dm3 (1)percentage yield = 4800/7200 x 100% = 66.7 % (1) ECF allowed for incorrectly balanced equation210biboth have the molecular formula C3H6 butthe arrangement of atoms is different (needs to explain the difference fully in their own words) (1)110biireagent: Br2 (aq) (1)reddish brown bromine decolourises when added to propene but remains unchanged when added to cyclopropane (1) 210cimovement: from vibrate about fixed position to move throughout the liquid (1)arrangement: from very close, orderly arrangement to close but disorderly arrangement (1)210ciihas a giant molecular structure and strong covalent bonds between atoms. (1)a lot of energy is needed to overcome the bonds. (1)2