2022 Punggol Sec Chemistry Answers

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Punggol Sec. Sch 1 MCQ P1 Qn Ans Qn Ans 21 C 31 A 22 B 32 B 23 D 33 A 24 A 34 B 25 A 35 C 26 B 36 C 27 D 37 D 28 C 38 B 29 D 39 A 30 C 40 D Paper 3 Section A Q1 suggested solution Other acceptable / not acceptable Feedback (a) (i) W [1] (ii) Y [1] (b) Steel is an alloy The layers of atoms of different sizes [1] cannot slide over each other easily [1] Q2 suggested solution Other acceptable / not acceptable Feedback (a) 2Fe + 3Cl2 → 2FeCl3 [2] Not balanced [1] (b) Iron is oxidised [1] The oxidation state of iron has increased from 0 in Fe to +3, in Fe3+ [1] Q3 suggested solution Other acceptable / not acceptable Feedback (a) (i) Fractional distillation [1] (ii) Difference in boiling points of nitrogen and oxygen. [1] (b) Relights a glowing splint [1] Glowing splint rekindles [1] (c) [1] : correct number of bonding electrons [1] correct number of unbonded electrons OO X X X X X X

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Punggol Sec. Sch 2 Q4 suggested solution Other acceptable / not acceptable Feedback oxides formula of oxide nature of oxide (acidic /basic /amphoteric) solubility in water sulfur SO2 acidic Yes [1] magnesium MgO basic [1] No [1] zinc ZnO [1] amphoteric [1] No [1] Q5 suggested solution Other acceptable / not acceptable Feedbacks (a) S [1] (b) X [1] (c) T and V [2] both must be correct (d) S [1] and W [1] Q6 suggested solution Other acceptable / not acceptable Feedback (a) (i) 2Li + 2H2O → 2LiOH + H2 The elements reacts with water to produce alkalis [1] and hydrogen (b) (i) The temperature is above the melting point is at 39 °C [1] The m.p is below 40 °C [1] (ii) Density is greater than 1 g/cm3 [1] Density is 1.53 g/cm3 [1], which is higher than density of water (c) Sodium floats on water [1] Reacts violently produces bubbles of gas / effervescence [1] Sparks of fire with orange coloured flame [1]

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Punggol Sec. Sch 3 Q7 suggested solution Other acceptable / not acceptable Feedback methane [1] [1] alcohol [1] [1] Q8 suggested solution Other acceptable / not acceptable Feedback A zinc carbonate B carbon dioxide C zinc nitrate D zinc hydroxide / zinc(II) hydroxide E ammonia Q9 suggested solution Other acceptable / not acceptable Feedbacks (a) A homologous series is a family of organic compounds with the same functional group [1]and similar chemical properties.[1] . (b) The flammability decrease [1] (c) (i) Mr of C5H11OH : 12(5) +11 + 16 +1 = 88 (ii) 138 °C 130 to 140 °C C H H H C H H H C C H H H C H H HO H H C

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Pun