VS 2021 O Level Pure Chemistry P1+P2 Answer Scheme

2020 Answer1 Victoria School2021 Chemistry O Levels / 6092Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20BBAABDCCCCDAADABDCDAQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40BDCBCCCADBBCBABCDACBPAPER 2 (SECTION A)QuestionAnswerMarkA1aipotassium and chlorine1aiichlorine1aiiicopper1aivaluminium1avpotassium and chlorine1bTrue, False, True, True3A2aPetroleum is heated and vapourised in a furnace before it enters the fractionating column.The vapours consist of different fractions, which have different boiling points.The fractionating column is cooler at the top than at the bottom. As the vapours rise up the column, they will cool and condense. Each fractions will condense at different temperatures.The smaller hydrocarbon, propane, has a lower boiling point will be distilled and collected at the top of the fractionating column while the bigger hydrocarbon, octane, has a higher boiling point and will be collected lower in fractionating column.111bPropane and butane are of similar sizes and have very similar boiling points. 1

2020 Answer2 ccompoundmolecular formulaempirical formulapropaneC3H8 C3H8octaneC8H18C4H9 2diOctane has a greater number of carbon and hydrogen atoms than butane. More carbon dioxide and water are formed in the combustion of octane than butane, hence more energy is released in forming of the bonds in water and carbon dioxide than absorbed in breaking the bonds in octane and oxygen.Energy is released in forming 8 more moles of carbon dioxide and 8 more moles of water in octane than butane. The This more than the energy absorbed in the breaking of bonds in the alkanes and oxygen. 11diinumber of moles of 50 kg octane = 50000 / 114 = 438.60 moltotal energy released from 50kg of octane = 438.60 x 5470 = 2399122 kJnumber of moles of butane required to produce energy = 2399122 / 2880 = 833.03 molmass of butane required = 833.03 x 58 = 48300 g = 48.3 kg111A3a1: hydrogen, oxygen2: hydrogen, chlorine4: copper, copper(II) ions2bIn experiments 1 and 2, carbon electrodes that were inert were used at the positive electrodes. This allowed anions in the solutions to be preferentially discharged and oxidised, forming substances like oxygen and chlorine.In experiment 4, copper electrodes that were not inert were used at the positive electrode. This caused the copper electrode to oxidise, forming copper(II) ions.11ciReddish brown solid is deposited on the negative electrode.1cii4OH-(aq)  O2(g) + 2H2O(l) + 4e- 1ciiiBlue solution turns colourless.The copper(II) ions were preferentially discharged at the negative electrode and concentration of copper(II) ions decreases. 11A4acalcium silicate1

2020 Answer3 CaSiO3biMaximum mass of iron = 112 / 160 x 14000 = 9800 tonnes3biiIron ore is a mixture containing iron(III) oxide mixed with impurities like sand and clay.Solid iron(III) oxide cannot be reduced completely with carbon monoxide.Iron could be oxidised back to iron(III) oxide due to presence of oxygen and high t