VS 2018 O Level Pure Chemistry P1+P2 Answer Scheme

2018 Answer1 Victoria School2018 Chemistry O Levels / 6092Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20BBCDAABCDBCCBBADCDBAQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40BAAADBDDADCDADBBDCCCPAPER 2 (SECTION A)QuestionAnswerMarkA1aiAmmonia, carbon dioxide1aiiSilicon dioxide1aiiiAmmonia1aivLead(II) nitrate1avAmmonia1bFalseTrueTrueFalse[Every 2 correct – 1 mark]2

2018 Answer2 A2ChlorineCopperMolten sodium chloride111A3Row 1: formulae of reagents used: CuO(s) / CuCO3(s) / Cu(OH)2(s)Row 2:formulae of salt: KNO3(s)method used: titration of KOH(aq) with HNO3(aq)Row 3:formulae of reagents used: Pb(NO3)2(aq) and H2SO4(aq) / (NH4)2SO4(aq) / Na2SO4(aq) / K2SO4(aq) or any Group I sulfate method used: ionic precipitation / addition of the two aqueous reagents / solutions, filtration to obtain the residue 1111A4aMetals contain positive ions in a ‘sea’ of delocalised electrons. The electrons can move to conduct electricity. In solutions of ionic compounds, the ions dissociate from the giant ionic lattice structure and can move to conduct electricity. 11bMetals remain unchanged when electricity is passed through.Solutions of ionic compounds break down into their elements/simpler substances when electricity is passed through.1A5aNitrogen: 78Oxygen: 21 1biThe density of helium is the lowest (0.17 g/dm3) as compared to the other gases and it would easily rise to the upper atmosphere and escape into outer space.1biiDensity of argon = 40/24 = 1.67 g/dm3 (to 3 s.f.)1

2018 Answer3 biiiThe percentage of helium in dry air is 0%, which means it cannot be obtained from fractional distillation of liquid air to be used for different purposes. Helium is also a finite resource on earth and should be conserved and used for more important purposes like MRI scanners in hospitals which will benefit patients, rather than on filling party balloons which is for leisure and not important. 11ci Helium nucleus contains2 protons and 2 neutrons. Argon nucleus contains 18 protons and 22 neutrons.1m – helium1m – argon 2 (ii)Both helium and argon are chemically inert. This is because both helium and argon have fully filled outermost electron shells of 2 and 8 electrons respectively. Hence they do not need to lose, gain or share electrons.11A6aThe temperature of 450 °C used in Stage 2 is lower than the temperature of 800 °C used in Stage 1. Hence, less energy is required to maintain a lower temperature in the reactor in Stage 2. The reaction in Stage 1 is endothermic so energy is taken in from the surroundings, compared to the exothermic reaction in Stage 2 which releases energy to the surroundings. Hence, the reaction in Stage 2 requires less energy. 11bCarbon monoxide is a toxic gas which reacts readily and irreversibly with haemoglobin to form carboxyhaemoglobin. This reduces the oxygen carrying capacity of the blood, leading to dizziness/fatigue and eventually death. 1

2018 Answer4 Burning carbon monoxide will produce carbon dioxide whi