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 –Punggol Sec. Sch 4 Q10 suggested solution Other acceptable / not acceptable Feedback (a) (i) Both Correct axes –[1] correct curve for X -end @10 min –[1] (ii) Correct curve for W [1] (b) At a higher temperature, more reactant particles gain more kinetic energy [1]. More particles possess/gained energy that is greater or equal than the activation energy [1] this results in a higher frequency of effective collision. [1] (c) (i) Mr of citric acid, C3H5O(COOH)3 : 36 +5 +16 + (12 +32 +3 ) (3) = 192 (ii) [c] in mol/ dm3 : 38.3 / 192 = 0.2 mol/ dm3 (iii) Mol of citric acid reacted : 0.2 X [100 /1000] = 0.02 mol (iv) Mol of CO2 produced: 0.02 X3 = 0.06 mol Volume : 0.06 X 24 dm3 = 1.44 dm3 volume of gas / cm time / min0 10 3 XW

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Punggol Sec. Sch 5 Q11 suggested solution Other acceptable / not acceptable Feedback (a) [1] : 3 repeating units, [1] : correct full structural formula (b) [1] (c) Land pollution / burning of plastics produces toxic gas / endanger marine / wildlife [2]. Any 2 (d) similar (e) (i) KMnO4 / potassium manganate(VII) [1] (ii) A mixture of ethanol and acidified potassium manganate(VII) [1] is heated [1]in a test tube. The colour of the KMnO4 changes from purple to colourless.[1] C H H C H C H H C H C H H C Cl H ClCl HC O OC H H H

SciChem 5076, 2022 Prelims S4E/5N-P1-P3 sol –Punggol Sec. Sch 6 Q12 suggested solution Other acceptable / not acceptable Feedbacks (a) pH is greater 7 / reacts with ammonium salts to produce ammonia/ taste bitter/ soapy/ reacts with acid to form salt and water only. Any [2] (b) (i) Mr : (14+4)(2) + 32+ 64 = 132 [1] (ii) mol of (NH4)2SO4 : 264 /132 = 2 mol [1] mol of Na2SO4 =2 mol mass : 2 X [ 23 (2) + 32 +64] = 284 g [1] (c) Using a pipette, transfer 25.0 cm3 of sulfuric acid into a conical flask. [1] Add a few drops of methyl orange indicator to the conical flask. [1] Add sodium hydroxide in a burette [1] and dispense/run the sodium hydroxide into the conical flask until the mixture turns orange/ peach. [1] The experiment is repeated again with the same volume of sodium hydroxide but without using the indicator[1]