VS 2017 O Level Pure Chemistry P1+P2 Answer Scheme

2017 Answer1 Victoria School2017 Chemistry O Levels / 5073Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20DCABCABDCCDCCADCCADAQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40ACADBDBBDDCCCACABACBPAPER 2 (SECTION A)QuestionAnswerMarkA1aiFe 1aiiH2 1aiiiCu 1aivO2 1avZn 1biCu, Fe, Zn1biiHigh melting and boiling pointsTransition metals and their compounds are good catalysts2

2017 Answer2 Forms coloured compoundsVariable oxidation states in their compounds[any 3 points – 2 marks, 2 points – 1 mark, 1 point – 0 marks]A2ai(aq), (aq), (s), (aq)[any 2 correct – 1 mark]2aiiFor reaction 1:The oxidation states of all the elements remain unchanged, hence this is not a redox reaction. For reaction 2, The oxidation state of X increases from -1 in AgX to 0 in X2. This is oxidation. The oxidation state of Ag decreases from +1 in AgX to 0 in Ag. This is reduction. Since oxidation and reduction occurs simultaneously, this is a redox reaction.11biyellow1biiAs the reactivity of the halogen increases, the rate of breakdown of the silver halide increases. 1A3aCombustion 1biphotosynthesis: 6CO2 + 6H2O  C6H12O6 + 6O2respiration: C6H12O6 + 6O2  6CO2 + 6H2O 11biiDuring photosynthesis, plants take in carbon dioxide from the atmosphere and decreases the amount of carbon dioxide in the atmosphere. During respiration, carbon dioxide is given out by plants and animals into the atmosphere and increases the amount of carbon dioxide in the atmosphere. 1cIn the long term, trees will die and undergo bacterial decay. The bacteria will break down the carbon containing compounds in the trees and release carbon dioxide into the atmosphere, which will contribute to the increase in the amount of carbon dioxide.11A4aiCatalytic cracking1

2017 Answer3 aiiThe heavier and longer chain hydrocarbons such as diesel and lubricating oil are in low demand but in large supplies. The lighter and shorter chain hydrocarbons such as naphtha and petrol are in high demand but in low supplies. Cracking helps to break down the heavier and longer chain hydrocarbons into lighter and shorter chain hydrocarbons to meet the demand for lighter and shorter chain hydrocarbons.11b [Any 2 of the above. 1 mark each] 2 creagentobservation for ethaneobservation for propeneaqueous bromineno visible reaction / solution remains reddish brownreddish-brown solution turns colourless / decolourises rapidly[3 correct – 2 marks, 2 correct – 1 mark, 1 correct – 0 marks]2diSimilarity: Both vegetable oils and alkenes contain carbon-carbon double bonds.Difference: Alkenes contain one carbon-carbon double bond but vegetable oils can contain more than one carbon-carbon double bond. 11

2017 Answer4 diiTo produce margarine, hydrogen is added to vegetable oils at a temperature of 200 °C and a nickel catalyst. [3 points – 2 marks, 2 points – 1 mark, 1 point – 0 marks]2A5aMost reactive: magnesium chromium cobaltLeast reactive: copper 1