SJI_2020 Year 3 EOY Chemistry 6092 ANSWERS

1 Y3 OP END OF YEAR EXAMINATION 2020 (ANSWERS) Paper 1 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 D C A B C B A C D D Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20 C A B D D A A C B B Q21 Q22 Q23 Q24 Q25 Q26 Q27 Q28 Q29 Q30 D B A A C C C B A C Paper 2 Section A A1(a)(i) Propanol is a flammable liquid. Or More even heating around the flask (ii) When evaporation occurs in figure 1.2, the vapours escape into the surroundings so less reactants are available for reaction. In figure 1.1, the liebig condenser condenses the vapours back into liquid state so more reactants are able to react in the flask to form more product. (b) (i) to react with the colourless / invisible (spots) to make them visible / coloured / seen (ii) The spot of sample 2 is more soluble as it has moved higher up the paper than sample 1. (iii) Rf = distance travelled by sample / distance travelled by solvent front (iv) sample 1 Rf = 0.20 to 0 .24 (show working) tartaric acid sample 2 Rf = 0.44 to 0.48 (show working) malic acid A2(a) The particles roll and slide over each other initially and vibrate at fixed positions thereafter The particles were closely packed and disorderly arranged initially and become closely packed, orderly arranged. (b) Temperature / ⁰C Time / s 80 69.3 30

2 (c) The liquid turns into a gas. Heat energy is absorbed and overcomes the intermolecular forces of attraction between the particles, causing the particles to move further apart from each other. A3 (a) 40 2,8,8 A3 (b) R has a stable electronic configuration, with eight electrons in its valence shell/has an octet electronic configuration, causing R to be inert. A3 (c) Atom Q loses two electrons to atom P, causing the electronic configuration of Q to change from 2,8,2 to 2,8. A3 (d) A3 (e)(i) Isotopes are atoms of t he same element with the same number of protons but different number of neutrons. Reject: same neutron number/nucleon number A3 (e)(ii) Isotopes of the same element possess the same number of valence electrons. A4 (a) CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) (b) Clear presentation/Calculating number of moles of both reactants Comparing molar volume or number of moles Correct identity of limiting reagent based on working/explanation Vol ratio of CH4 : O2 = 1:2, 10 cm3 of CH4 requires 20 cm3 of O2 for complete reaction. 20 cm3 of CH4 requires 40 cm3 of O2 which is less than the 60 cm3 of O2 available. O2 is in excess and CH4 is limiting reagent. XX P S XX XX OO O X O X X X S XX OO X X

3 (c) Vol ratio of CH4 : CO2 = 1:1 Volume of CO2 produced = 20.0 cm3 Volume of O2 remaining = 60 - 40 = 20.0 cm3 Total volume = 20 + 20 = 40.0 cm3 (d) Actual volume of CO2 produced = 0.7 * 20cm3 = 14.0 cm3 A5(a) Ba(NO3)2 + K2SO4 → BaSO4 + 2KNO3 Ba2+ + SO42- → BaSO4 A5(b) Sulfuric acid/ sodium sulfate solution (any