VS 2015 O Level Pure Chemistry P1+P2 Answer Scheme

2015 Answer1 Victoria School2015 Chemistry O Levels / 5073Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20BDDBCBAABDCCDCABADCBQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40DBDBBCDCAAADBABBCBCAPAPER 2 (SECTION A)QuestionAnswerMarkA1aA – non-metalB – metalD – metalE – non-metal 1biC 1biiA 1biiiB 1cThe elements in the table form different compounds by gaining or losing electrons, hence they have different oxidation states. For example, Element A has an oxidation state of -2 as it gains two electrons to form an ion of charge 2-. Since, Group 0 elements have a fully filled valence/outermost electron shell, they do not bond with any other elements to form compounds, hence do not have any oxidation states. 11

2015 Answer2 A2aiAs the reactivity of the metal decreases, the temperature needed for the reduction of its oxide decreases. 1aii700°CIron is less reactive than zinc but more reactive than lead.Hence the temperature needed to reduce iron oxide with carbon is lower than 900°C but higher than 400°C. 11bMetal: MagnesiumMetal oxide: Silver Oxide1cZinc oxide andHydrogen11A3aName of compoundStructural formulaProcess(es) used to manufacture the compound ethene Fractional distillation of crude oil / petroleum followed by catalytic crackingpoly(ethene) Addition polymerisation of etheneethanol Two separate processes can be used. Process 1: Catalytic addition of steam to ethene. Process 2: Fermentation of glucose 112

2015 Answer3 ethanoic acid Oxidation of ethanol1biBoth acids react with metal oxides to form salt and water only in a neutralisation reaction. 1biiDilute ethanoic acid is a weak acid while dilute hydrochloric acid is a strong acid. Hence, ethanoic acid undergoes partial dissociation when dissolved in water but hydrochloric acid undergoes full dissociation when dissolved in water. The concentration of hydrogen ions is lower in ethanoic acid than hydrochloric acid, thus lower frequency of effective collisions between the hydrogen ions and metal oxide particles so the rate of reaction in ethanoic acid is slower than in hydrochloric acid.11A4a600 – 700 °C1bExtraction of aluminium from bauxite requires the ionic solvent to be heated to 900 °C compared to recycling used cans which only requires heating to 700 °C, hence more heat energy is required for extraction from bauxite. Also, extraction of aluminium from bauxite makes use of electrolysis which requires electrical energy. Both processes increase the use of energy in extraction from bauxite. 11cConcentrated sodium hydroxide is very caustic/corrosive and causes harm to living tissues, such as chemical burns and skin irritation.Carbon dioxide is a greenhouse gas which traps excess heat in the atmosphere. This leads to global warming which will result in ice caps melting, sea levels rising and causing flooding in low lying areas. 11dAluminium is a finite resource and hence recycling helps to conserve natural resources / Land will be free for other purposes