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 high