VS 2019 O Level Pure Chemistry P1+P2 Answer Scheme

2019 Answer1 Victoria School2019 Chemistry O Levels / 6092Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20ABCDDDCBACDCBCADDBBAQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40CACCABBAAADACABBBCDAPAPER 2 (SECTION A)QuestionAnswerMarkA1aD and G 1bA and E 1cC 1dG 1eA 1A2aIsotopes are atoms of the same element with the same number of protons but different number of neutrons. Isotopes 1, 2 and 3 have the same number of 16 protons but different number of neutrons, i.e. 13, 14 and 15 respectively. 11bThe data shows that all 3 isotopes have the same number of 6 outer shell electrons. The isotopes have the same chemical reactions as they are in the same group. 1

2019 Answer2 ciX: sulfurY: oxygenZ: zinc 1ciilowest melting point: Y (oxygen) X (sulfur)highest melting point: Z (zinc)Z (zinc) has the highest melting point as it has a giant metallic structure so a lot of energy is used to overcome the strong metallic bonds between the positive ions and sea of delocalised electrons. X (sulfur) and Y (oxygen) both have simple molecular structures. However, X has a higher relative molecular mass than Y, hence more energy is used to overcome the weak intermolecular forces of attraction in X, hence higher melting point than Y. 111ciiiZZ is a reactive metal and metals react with dilute acids to form salts and hydrogen gas. 11A3aLead is a reactive metal which can react with dilute nitric acid. Gold is a less reactive metal than lead and cannot react with dilute nitric acid. 11bLead compounds react with dilute nitric acid to form lead nitrates which are soluble in water.Lead compounds react with dilute hydrochloric acid and dilute sulfuric acid to form lead chlorides and lead sulfates respectively, which are insoluble in water. 11ciLead and aluminium ions react with aqueous ammonia to form a white precipitate which is insoluble in excess aqueous ammonia. Hence, it is not possible to distinguish between lead and aluminium ions. Zinc ions react with aqueous ammonia to form a white precipitate which dissolves in excess aqueous ammonia to form a colourless solution. Hence, only zinc ions can be identified.11ciiAdd aqueous sodium chloride (or any other solutions containing chloride ions) to the solutions of lead ions and aluminium ions. 1

2019 Answer3 There will be a white precipitate observed for the solution of lead ions but no visible reaction for the solution of aluminium ions.[Note: can also add any solutions containing iodide ions. Yellow precipitate will be formed for the solution of lead ions] ciiiAdd excess aqueous sodium hydroxide to the solution, followed by a piece of aluminium foil. Warm gently. Effervescence of colourless and pungent gas will be observed. Gas turns moist red litmus paper blue, so ammonia gas is given off. 111A4aNH3(g) + HCl(g) → NH4Cl(s)1m – balanced equation1m – state symbols2bidistance travelled / cmMrNH36017HCl4036.51biiNo [must state but not marks]As the