2024 Fuhua Sec 4E Chemistry P2 answers

1 FUHUA SECONDARY SCHOOL Sec 4E Chemistry 6092 Preliminary Examinations 2024 – Mark Scheme PAPER 2 Section A [70 marks] Q Answer Mark Remarks 1a Q and R 1 b ZT2 1 ci shared electrons non-bonded electrons 1 1 cii Charge of Mg2+ and M3- [;] Three Mg2+ and two M3- [;] Outer electrons for Mg2+ and M3-[;] 2 3; [2] d true false Molecule 3 has lower boiling point then molecule 2. ✓ Molecule 3 is a saturated organic compound. ✓ Element Z reacts with oxygen to form acidic oxide only. ✓ Elements P and T are in Group 16. ✓ 2 4✓ [2] Total 8 marks 2ai Mass of CO2 = 100 – 97.8 = 2.2 g Moles of CO2 = 2.2 / 44 = 0.05 mol 1 ii experiment particle size volume of acid / cm3 concentration of acid / mol/dm3 1 powder 50 e.c.f from (a)(i) mole 2.0 2 lump 200 [1] (must be 4x of expt 1/ 2x of expt 3) 1.0 3 Powder [;] Same as expt 1 100 [;] 2x of expt 1 2.0 [;] Same as expt 1 Expt 1: mole of H+ = 0.05 x 2 = 0.10 mol Volume of acid = 0.10 / 2.0 = 0.05dm3 = 50 cm3 1 1 1 3; [1] 2b As particle size decreases[;], there is a larger exposed surface area[;] of barium carbonate in contact with the acid. There are more collisions and increase in frequency of effective collisions between barium carbonate and H+ ions the acid particles[;], hence increasing speed of reaction[;]. 2 4; [2] 2; [1] c Add aq. silver nitrate solution to each acid, if white ppt forms, the acid is HCl. OR Add aq. NaOH, aluminium foil to each acid and heat the mixture, if ammonia gas is produced (moist red litmus turns blue), the acid is HNO3. 1

2 d Rate will be slower [;] and change in mass will be the same [;] as experiment 1. Ethanoic acid is a weak acid which dissociates partially in aqueous solution to give a lower concentration of H+ ions [;] compared to the strong acid, hence rate is slower. The acid / H+ ions remains as the limiting reagent / same number of moles of H+ ions used [;] hence mass of gas produced is the same and same change in mass of the reaction. 3 4[;] – [3], 2-3[;] – [2], 1[;] – [1] Total 10 marks 3ai Concentration of CuSO4 decreases [;] from 1.10 mol/dm3 until all Cu2+ ions in solution reduced to form Cu at the cathode. [;] Cu2+(aq) + 2e → Cu(s) [;] 2 3; [2] ii Amount of Cu deposited = 200/1000 X (1.10 – 0.22) = 0.176 mol Mass of Cu = 0.176 X 64 =11.3 g 1 1 bi straight horizontal line at 1.10 g 1 ii Colourless gas given off at the graphite electrode. Grey / silvery solid deposited on the iron object. 1 1 c Once tin is scratched, iron will lose electrons / oxidise more readily to form iron(II) ions as tin is less reactive than iron 1 1 Total 9 marks 4a butyl propanoate[;], butanol[;], propanoic acid[;] , addition of hydrogen Accept catal