2020 SNGS Y4IP EOY Answers

SNGS Mark scheme for Year 4 IP EOY 2020 Paper 1 Answers to Section A: Circle the most appropriate answer to each question. 1 A 11 D 2 B 12 A 3 C 13 A 4 B 14 B 5 A 15 D 6 D 16 D 7 C 17 C 8 B 18 D 9 A 19 C 10 D 20 A 21 D 31 B 22 C 32 B 23 C 33 C 24 B 34 D 25 C 35 B 26 D 36 A 27 C 37 D 28 D 38 D 29 A 39 B 30 D 40 D

2 SNGS Mark scheme for Year 4 IP EOY 2020 Paper 2 Section A (50 marks) A1 a Manganese(IV) oxide OR Nickel [1] b Ammonium chloride [1] c Calcium carbonate [1] d Lead(II) hydroxide [1] e Aluminium sulfate [1] f Ammonium chloride OR Iodine [1] A2 a Y [1] b Flat, horizontal line drawn at 55 °C Flat, horizontal line drawn at 80 °C Vertical lines at other parts of the graph Start and end at the given temp range [1] [1] c 4/6 = 0.67 Not in 2 dp: -1/2 m [1] d Yes, substance Y and the toxic dye have the same Rf value. [1]

3 e Pencil lead is insoluble in water / the solvent, hence it will not be separated together with the toxic dye and interfere with the results OR Pen ink is soluble in water / the solvent, hence it will be separated together with the toxic dye and interfere with the results [0.5] [0.5] A3 a Structure V [1] b Structure III [1] c Structure I and II [1] d Molecules Far apart, randomly arranged High speed in all directions [1] [0.5] [0.5] e Has a giant ionic structure In the solid state, there are strong electrostatic forces of attraction between oppositely charged ions Ions can only vibrate about fixed positions No mobile ions to conduct electricity [0.5] [0.5] [0.5] [0.5] A4 a Use acidified aqueous potassium manganate(VII) missing aqueous/solution or (VII) or wrong spelling: minus ½ Turns it from purple to colourless [1] [0.5] [0.5] b Cu2S is reduced as The oxidation state of copper decreased from +1 in Cu2S to 0 in Cu Cu2S is also oxidised as The oxidation state of sulfur increased from -2 in Cu2S to +4 in SO2 [0.5] [0.5] [0.5] [0.5] [0.5] [0.5] c CaCO3 + SO2 → CaSO3 + CO2 [1m] OR SO2 + H2O → H2SO3 CaCO3 + H2SO3 → CaSO3 + CO2 + H2O [award 1/2 m if any one equation above is balanced & correct] Wrong formula = 0 m [1] A5 a Increases [1] b Number of electron shells / atomic radius / size increases down the group distance between sea of delocalized electrons and positive ion increases Electrostatic forces of attraction decreases Less energy required [0.5] [0.5] [0.5] [0.5]

4 c Effervescence (of a colourless, odourless gas) is observed. Gas extinguished lighted splint with a pop sound [1] [1] d Down Group II, the metals/elements become more reactive. Hence their (metal) carbonates become more thermally stable If student did not differentiate and state the metals and their carbonates explicity: max 1 mark [1] [1] e No, strontium is more reactive than calcium OR magnesium Hence its oxide is very stable and cannot be reduced by carbon. If student did not differentiate and state the metals and their oxides explicity: max 1 mark [0.5] [0.5] f She will not succeed as Calcium is more reactive than magnesium Calcium has a higher tendency to lose electrons Calcium will oxidise first / corrode in place of magnesium [1] [0.5] [0.5] g F2 F – 0m Fluorine – 0.5m [1] A6 a Mol of MgCO3 = 8.4 / 84 = 0.1 mol Mol of HCl = 0.1 x 1 = 0.1 mol MgCO3 + 2HCl → MgCl2 + CO2 + H2O Mol of CO2 produced = 0.1 / 2 = 0.05 mol Vol of CO2 produced = 0.05 x 24 = 1.2 dm3 [1] [1] bi Gentler slope / gradient Ends at the same volume as graph A [0.5] [0.5]

5 bii steeper slope / gradient ends at double the volume of graph A allow ecf if (a) is wrong [0.5] [0.5] c Sulfuric acid is dibasic while hydrochloric acid is monobasic Concentration of H+ ions in sulfuric acid higher than / double / twice of hydrochloric acid Higher frequency of collisions and effective collisions Hence faster rate [0.5] [0.5] [0.5] [0.5] d No, ethanoic acid will not dissociate / ionize in ethanol to form mobile H+ ions Only mentioned no presence of water: ½ m [0.5] [0.5] e She did not add the same volume / same moles of acid and hydroxide to each other OR did not add reactants in the same molar ratio Hence, potassium nitrate may be contaminated with excess acid or hydroxide Carry out titration [0.5] [0.5] [1] A7 a I- [1] b Al3+ [1] c Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s) -1 m for any wrong state symbol(s) -1 m if not balanced Wrong formula = 0 m [2] d Pale green solution turns colourless Grey solids produced [1]

6 Section B (30 marks) B8 a 70 +/- 5 atm, 200 °C 930 +/- 10 atm, 300 °C [1] [1] b 70 +/- 5 atm, 200 °C use less energy / requires lower pressure hence lower costs / safer to carry out the reaction OR 930 +/- 10 atm, 300 °C requires higher(very high) pressure / temperature higher rate of reaction [0.5] [0.5] c Increase surface area to volume ratio More surfaces for particles to collide against Higher frequency of collisions and effective collisions Hence increases rate [0.5] [1] [0.5] d 2 moles of NH3 produced has an energy change of -92 kJ 4 moles of NH3 produced has an energy change of -92 x 2 = -184 kJ No or wrong unit -1/2 m No “-“ -1/2 m [1] e Ionic compound = 0m Missing any lone pair or additional electrons: -1m [2] f 944 + 2(436) –[163 + 4(391)] = +89 kJ / mol wrong unit -1/2 m No “+“ -1/2 m [0.5] [0.5] [1] g Correctly labelled axis ½ m Labelled reactants and products correctly ½ m Ea labelled and directional arrows drawn correctly ½ m ∆H labelled and directional arrows drawn correctly ½ m [2]

7 B9 a 2 x 2 = 4 mg Wrong unit -1/2m [1] b N O Mass (%) 46.7 100-46.7 Mol 46.7/14 = 3.336 53.3/16 =3.331 Simplest ratio 1 1 x = 1 OR [14 ( 14 + 16x)] × 100 = 46.7 x = 1 [1] [1] c Nitrogen monoxide can be oxidized to nitrogen dioxide and Nitrogen dioxide can dissolve in clouds/water to form nitric acid or acid rain Acid rain corrodes buildings made of cement / limestone / metals OR Decreases pH of soil, killing plants / unsuitable for plant growth OR Decreases pH of oceans, killing marine life OR Causing respiratory problem Allow ecf if b is NO2 [0.5] [0.5] [1] d 2NO + 2CO → 2CO2 + N2 -1/2 m if not balanced, Wrong formula = 0 m [1] e There will be less dissolved oxygen in the ocean Marine creatures might suffocate / die / will not thrive or survive [1] [1] B10 Eit her a Lithium metal: anode (-) Titanium disulfide: cathode (+) Mark labelling and charge independently, 0.5m each [1] [1] b Lithium has the lowest relative atomic mass compared to other metals OR Among all the metals in the periodic table, lithium has the lowest relative atomic mass [1] ci Cobalt(IV) oxide is a stronger oxidizing agent. It generates a larger voltage / potential difference [1] [1] cii LiC6 + CoO2 → C6 + LiCoO2 -1/2 m if not balanced Wrong formula = 0 m [1]

8 d Anode: Magnesium electrode becomes smaller/thinner cathode: Pink/reddish brown solid deposited / blue colour of electrolyte fades / electrode increases in size [1] [1] e Simple cell is not rechargeable / magnesium has to be replaced OR Simple cell generates more waste Not portable. Magnesium-copper simple cell produces a lower voltage (2.69 V compared to 4 V) [1] [1] B10 OR a Any concentrated soluble aqueous chloride Except CuCl2 [0.5] [0.5] b 4OH- → 2H2O + O2 + 4e- -1 m if not balanced Wrong formula = 0 m [1] c Mol of Cl2 gas = 2.