RVHS 2023 Chem Sec 3 Paper 1&2 ANS

RIVER VALLEY HIGH SCHOOL 2023 SEC 3 END-OF-YEAR EXAMINATION CHEMISTRY Paper 1 1 2 3 4 5 6 7 8 9 10 C B D A C B D D D B 11 12 13 14 15 16 17 18 19 20 D D D C B B B A C D 21 22 23 24 25 26 27 28 29 30 D B D A A B B B A A Paper 2 Section A A1 (a) A and E (b) D and E (c) B and F (d) D A2 (a) Box A Box B (b) At a lower temperature, particles lose KE, move slower and closer together / more particles per unit volume. This increases air density and increases lift, making it easier for the smaller plane to take off.

(c) (i) (ii) Test the gas collected with a moist blue litmus paper. If the gas does not cause the moist blue litmus paper to turn red, it shows that there is no acidic gas present / absence of NO2 gas. A3a (i) (ii) (iii) N2 ≡ 3H2 H2 is the limiting reagent Theoretical yield = 300/3 x 2 = 200 cm3 Actual yield = 20.0cm3 % yield = 20/200 x 100 = 10.0% (iv) Increase the pressure / Lower the temperature (b) 2NH3 + H2SO4 → (NH4)2SO4 c(i) nNH3= [4800/1000] / 24 = 0.2000 mol nH2O= 7.20 / [2(1.0) +16.0] = 0.4000 mol x = 0.2000 / 0.100 = 2 y = 0.4000 / 0.100 = 4 Hence, N2O4 c(ii) NO2 Gas syringe mixture of NO and NO2 gases NaOH(aq)

A4a (i) Aqueous iodine is brown (ii) Na2SO4 or sodium sulfate [ (iii) element oxidation state in reactant oxidation state in product copper +2 +1 iodine -1 0 (iv) Copper. Cu2+ /Cu/ Copper/CuSO4 gained electrons b (i) Manganese / Mn / MnO4– is reduced as the oxidation state of Mn decreased from +7 in MnO4– to +6 in MnO42– (ii) MnO42– + …2…H2O + …2…e– → MnO2 + 4OH– (iii) MnO2 is an insoluble solid (iv) Substance X is a reducing agent A5 (a) 2nd series coin – aluminium & bronze. Al has a relatively low / lowest density of 2700 kg/m3 compared to other metals (b) Both 1st and 2nd series of coins are made of alloys. In an alloy, the different size of atoms disrupts the orderly arrangement of atoms in pure metals. Hence, the layer of atoms cannot slide easily in an alloy (brass vs copper) . Hence coins made from mixture of metals are stronger / harder. (c) Copper has a higher melting point (1083oC) than brass (950oC) OR iron (1536oC) has a higher melting point than steel (1510oC). d(i) A lot of energy is required to overcome the strong electrostatic attraction between metal cations and (sea of) delocalised / mobile valence electrons. Hence it does not have the ability to expand upon heating. (ii) Diamond has a giant covalent structure while poly(tetrafluoroethene) has a macromolecular structure. More energy is required to overcome the strong er covalent bonds between the carbon atoms than the weaker intermolecular forces of attraction between the poly(tetrafluoroethene) molecules. Hence, diamond has a lower CTE than poly(tetrafluoroethene). (iii) • Hard • Non-conductor of electricity • Insoluble in all solvents / water • High melting & boiling points

Section B B6 (a) A weak acid is a substance that partially ionises / dissociates in water to produce / form H+ ions. (b) H2CO3 (aq) ⇌ H+ (aq) + HCO3─ (aq) (c) Ocean acidification would also dissolve / react with the shells of calcifying organisms. Carbonic acid can react with calcium carbonate to form calcium bicarbonate (soluble in water), water and carbon dioxide. (d) (i) Sodium chloride / NaCl and sodium carbonate / Na2CO3 These salts are soluble in water. The reagents that are used to make these salts are also soluble in water. (ii) Repeat the titration without using the indicator. Evaporate the resulting mixture / aliquot to dryness. B7 (a) Solution P (b) RNH2 (g) + H2O (aq) ⇌ RNH3+ (aq) + OH─ (aq) (c) (i) Solution P is neutral as the universal indicator is green in colour. Solution P has the same number / concentration of H+ ions and OH─ ions. (d) (i) The solubility of Group 2 sulfates decreases down the group. (ii) 9.44 x 10-6 Accept: any value in the range of 10-6. (ii) Add an excess of magnesium oxide/ magnesium hydroxide/ magnesium/ magnesium carbonate to dilute sulfuric acid until no more solid dissolves / no more effervescence observed. Filter to collect the filtrate. Evaporate the filtrate to dryness.