VS 2023 O Level Pure Chemistry P1+P2 Answer Scheme

2023 Answer1 Victoria School2023 Chemistry O Levels / 6092Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20BADBADBDCBABDCCACBACQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40DACDBDBDCCDACBDBCABAPAPER 2 (SECTION A)QuestionAnswerMarkA1aY: 2, Li+Z: VI, Se2- 22bF-.Since number of protons = number of electrons and the mass number is given by total number of neutrons + total number protons. Thus, the mass number of X (i.e. 10+9 = 19) is the same as the relative atomic mass shown on the Periodic Table.11cHeliumdNo observable changeBromine is less reactive than fluorine, thus bromine unable to displace fluorine from its salt solution. [reject if fluoride is used in place of fluorine]11

2023 Answer2 A2aNegative electrode: silverPositive electrode: oxygen gas11bWhen passing through platinum electrodes (metal): there are mobile electrons, hence platinum remains chemically unchanged. When passing through the solution (ionic compound): mobile ions in the solution act as mobile charge carriers. (Thus, at the cathode (negative electrode), Ag+ is selectively discharged to form silver metal. While at the anode (positive electrode), OH- is selectively discharged to form oxygen gas / The electrolyte decomposes.)11ccompound: nitric acid/HNO3 [Reject: H+ ions]explanation: Since Ag+ and OH- were selectively discharged, only H+ and NO3-ions are left remaining in the solution.11diHydrogen gasdiiAll the Ag+ has been preferentially discharged at the start of the electrolysis (gain electrons more readily) and leaving behind only H+ ions in the solution. Hence, H+ions are discharged and hydrogen gas is formed.Reject: silver ions less reactive than hydrogen ions.A3ai4CuFeS2 + 11 O2  4Cu + 2Fe2O3 + 8SO21m for correct reactants and products1m for balanced equation2aiiMass of Cu in 1 tonne of chalcopyrite= = 347.8 kg = 348 kgMass of Cu in tonnes = 0.348 tonnes (3sf)1 for working1biAcid: silicon dioxideBase: iron(III) oxide1biiBasic compound used in the extraction of iron is calcium oxide which is obtained from the thermal decomposition of calcium carbonate, whereas the basic compound used in the extraction of copper is iron(III) oxide.The molten slag formed in the extraction of iron is calcium silicate, instead of iron silicate. [not in syllabus]11cCO2 and H2O [1m each] Reject: hydrogen gasExplanation: 4CuO + CH4  4Cu + CO2 + 2H2O 2

2023 Answer3 A4aThe ratio of atoms of metal to atoms of oxygen decreases [1] from 2 :1 in Li2O to Na2O, to 1 : 1 ratio in Na2O2 and K2O2, to 1 : 2 ratio in KO2 [1]. 2b 1 m for bonded electrons and correct charge1 m for ‘extra’ electron added to each ion2ciO2- 1ciiOne of the oxygen atoms in the superoxide ion does not have a fully filled valence electron shell1diGroup 1 metal hydroxides dissociate in water to form OH- so the solution turns blue.Hydrogen peroxide is a bleach, which is a substance that removes colour/bleaches, so the solution turns colourless.Oxygen is produced (from decomposition of hydr