Copy of 2024 ANDSS 4E Chem Prelim P2 ANS

EXAM ANSWERS Year: 2024 Exam: Prelim Level/Stream: 4E Subject: Chemistry 6092 P2 Qn Answer Marks Comments 1 a i ii iii iv v chlorine and oxygen iron(II) chloride argon carbon and chlorine iron and iron(II) chloride 5 1m each A1 b Addition reaction with hydrogen ACCEPT: Hydrogenation / Addition with Hydrogen / addition of H2 Esterification Neutralisation ACCEPT: neutralization REJECT: acid-alkali reaction 3 1m each Qn Answer Marks Comments 2a The mass of the mothballs decrease / becomes smaller over time. REJECTED: Mothballs become smaller / reduce in size / shrink. This indicates that the mothball is gradually disappearing, which can be explained by sublimation, where the mothball turns from a solid into a gas without going though the liquid state. ACCEPT: sublimation / solid sublimes to form gas / solid particles gain sufficient energy to overcome forces of attraction and become gas/gaseous particles. REJECT: decomposition 2 1 - trend 1 - reason

Page 2 of 12 2b Diffusion is the movement of gas molecules from a region of higher concentration near the mothballs to a region of lower concentration throughout the cupboard. As the molecules are spread out and mixed with the air molecules, the pungent smell can be observed. / Gas molecules (of mothball) collide/ mix with molecules in the air and spread across the room/space. REJECTED: travel / move 1 1 1m – diffusion definition on solute movement 1m- mixing with air molecules Qn Answer Marks Comments 3a i Fractional distillation REJECTED: distillation, fractionating distillation 1 3a ii In the furnace, the crude oil is heated into a vapour / heated and vapourise before it enters the fractionating column. The vapour contains a mixture of hydrocarbons with different boiling points. As the vapour rises up the column, the fractions with lower boiling points rise further up the column and condense at a lower temperature while the fractions with higher boiling points condense at a higher temperatures and collect at the lower part of the column. / As the vapour rises up the column, the fractions with higher boiling points condense and are collected at lower down the column while the fractions with lower boiling points rise further up the column to be collected. Jet fuel is collected as one of the fractions. 1 1 3b Used cooking oil contains impurities such as water. As the used cooking oil is placed in the separating funnel, the mixture separates into different layers based on density differences. When allowed to settle, the liquid that is denser can be tapped off from the bottom, the remaining layer will be the processed oil. (OWTTE) 1 1 Qn stated water as impurities; water is denser than cooking oil and settles at the bottom layer.

Page 3 of 12 3c Carbon dioxide is released /produced/given out duri