VS 2016 O Level Pure Chemistry P1+P2 Answer Scheme

2016 Answer 1 Victoria School2016 Chemistry O Levels / 5073Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20CDBCBDACBDCADCCABBACQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40CBCCAABDCBCACBDDDADCPAPER 2 (SECTION A)QuestionAnswerMarkA1atrendonly true down a grouponly true across a periodtrue for bothThe number of electron shells increases.✔The number of valency electrons increases.✔Proton number increases.✔There is a change in character from metallic to non-metallic. ✔[2 correct – 1 mark]2

2016 Answer 2 biMelting point decreases down Group I and increases down Group VII.1biiReactivity increases down Group I and decreases down Group VII. 1cCatalysts increase the rate of reaction hence the industrial processes can be completed in a shorter time. This will help to reduce energy usage and save costs. Only a small amount of catalysts is needed and they remain chemically unchanged and unchanged in mass at the end of the reaction, so they can be reused indefinitely and there is no recurring costs.Hence, they reduce costs in the long run.11A2aRusting involves oxidation. The oxidation state of iron increases from 0 in Fe to +3 in Fe2O3. Extraction involves reduction. The oxidation state of iron decreases from +3 in Fe2O3 to 0 in Fe. 11biAn alloy is a homogeneous mixture of metal with (small amounts of) other elements. 1biiThe oil, the paint and the plastic coating acts as a protective layer to prevent the iron parts of the bicycle from rusting as they prevent the iron from being exposed to water and oxygen. 11biiiZinc is more reactive than iron and hence its atoms will lose electrons more readily and corrodes in place of iron. 11A3aThe actual surface temperature of Mercury is close to its predicted surface temperature as there is no atmosphere of gases. [must state but no marks]The actual surface temperatures of Earth and Venus are higher than their predicted surface temperatures. This is because their atmospheres contain carbon dioxide which is a greenhouse gas. Carbon dioxide traps excess heat which increases the surface temperature. The difference between the actual surface temperature and predicted surface temperature is much higher for Venus than Earth (by 500°C) as the atmosphere of Venus contains 97% carbon dioxide but the atmosphere of Earth contains only 0.04% carbon dioxide. 11

2016 Answer 3 biVolcanic eruptions1biiThe pH of the water will be low/ less than 7.1biiiThe surface temperature of Venus is too high at 462°C hence the water would have boiled as its boiling point is 100°C and formed steam/water vapour. 1ciPlants undergo photosynthesis where they take in carbon dioxide and release oxygen. Hence the percentage of carbon dioxide decreased and the percentage of oxygen increased. 11ciiIncrease in industrial activities, use of machinery and vehicles which results in increased combustion of fossil fuels or carbon containing fuels which releases (excess) carbon diox