NYGH 2022-S3EOY-IP Chem P1 and P2 Ans

Secondary 3 (IP) EOY Answers 2022 Sec 3 End-of-Year Exam Chemistry Answers Paper 1 1 B 2 B 3 B 4 A 5 C 6 B 7 D 8 B 9 C 10 C 11 A 12 A 13 B 14 D 15 C 16 B 17 D 18 C 19 B 20 C 21 D 22 D 23 D 24 C 25 A 26 C 27 B 28 D 29 B 30 C Qn Ans Explanation 1 B A: False, state 1 is changed to state 2 by boiling, not melting. B: True C: False, state 2 is gaseous state, so particles are moving randomly at high speed. D: False, state 3 is solid state. 2 B Mr of NH3 (17.0) is lower than that of CO2 (44.0), so NH3 will diffuse faster than CO2 and reach moist blue litmus paper first. NH3 will have no effect on moist blue litmus paper. When CO2 reaches the moist blue litmus paper, it will turn moist blue litmus paper red. Overall observation: Moist blue litmus paper turn red. 3 B Impurities increase boiling point and decrease melting point. 4 A Carbon dioxide is formed from the reaction between hydrochloric acid and calcium carbonate. Since carbon dioxide is acidic, an acidic or neutral drying agent should be used to dry the gas  from the options only concentrated sulfuric acid is suitable. Since carbon dioxide (Mr of 44.0) is more dense than air (average Mr of approximately 28.8), downward delivery should be used. 5 C Step 1: Sublimation is done to remove ammonium chloride. Note that sublimation cannot be done after the substance is dissolved in water. Step 2: Water is added to dissolve copper(II) chloride. Silver chloride remains insoluble. Step 3: Filtration is done to remove insoluble silver chloride. Step 4: Hydrated copper(II) chloride is obtained by crystallisation. 6 B 1: False, eg N2 is a molecule and an element 2. False, eg N2 is a molecule and an element 3: True, generally metals and non-metals react to form ionic compounds 7 D Proton number for Y = 79 + 2 = 81 Nucleon number for Y = 197 + 2 + 1 = 200 (add both protons and neutrons) Since 2 protons are added while only 1 electron is added, Y will have a positive charge.

From the above, answer will be option D. 8 B P: H Q: Group 1 element (Li) R: Group 16 element (O) S: Group 18 element (Ne) A: Form ionic compound, LiH with high melting point B: Form simple covalent compound, H2O with low melting point C: Form ionic compound, Li2O with high melting point D: Option can be eliminated since S is a noble gas that is inert and will not form compounds. 9 C Since total abundance must add up to 100%, x + 0.5x + (x – 0.2) = 1 x = 0.48 20(0.48) + 21(0.24) + 22(0.28) = 20.8 10 C From the structure of N2H4, there are 2 valence electrons not involved in covalent bonding for each N atom. There are 2 more inner shell electrons in each N atoms that are not involved in covalent bonding. Therefore there are 8 valence electrons not involved in covalent bonding in the molecule. 11 A Sulfur dioxide is used as a bleaching agent while sulfuric acid is used for the other stated purposes. 12 A For the titration of a weak acid with a strong base, the starting pH is around 3-4 and the ending pH is around 13-14. The mid-point of the vertical region of the graph should be higher than 7. 13 B acidic oxides: CO2, SO3 basic oxides: CaO neutral oxides: NO amphoteric oxides: PbO, Al2O3 14 D Options A and B show reactions between an alkali / base and an ammonium salt while option C shows a neutralisation reaction. 15 C Calcium sulfate is an insoluble salt best prepared by precipitation using two aqueous solutions. A solution of calcium nitrate will be obtained as the filtrate in the first step of option C. 16 B For option A, the indicator would be blue both before and after pH 9. For option C, the indicator would be yellow at pH 1.

For option D, the indicator would be able to distinguish between the two acids since it has a different colour at pH 1 compared to pH 5. 17 D theoretical yield of of iron = 5000 ÷ 159.6 × 2 × 55.8 ÷ 1000 = 3.496 kg % yield = 2.83 / 3.496 × 100% = 80.9% 18 C mass of pure H2O2 = 1650/24000 × 2 × 34 = 4.675 g % purity = 4.675 / 9.62 × 100% = 48.6% 19 B Mr of butane = 3.48 ÷ (1440 / 24000) = 58.0 let molecular formula of butane be C2nH5n n = 58.0 ÷ 29.0 = 2 molecular formula = C4H10 20 C volume of O2 needed to react completely with 160 cm3 of NH3 = 160 ÷ 4 × 3 = 120 cm3 < 160 cm3 NH3 is the limiting reactant volume of N2 formed = 160 ÷ 4 × 2 = 80 cm3 volume of unreacted O2 = 140 – 120 = 20 cm3 Total volume of resultant gas mixture = 80 + 20 = 100 cm3 21 D no. of moles of SO2Cl2 in 25.0 cm3 solution = 0.350 ÷ 135.1 = 0.0025907 For every 1 mole of SO2Cl2 reacted with water, there are 4 moles of H+ ions produced. H+(aq) + OH−(aq)  H2O(l) no. of moles of KOH needed for titration = no. of moles of H+ ions in 25.0 cm3 solution = 0.0025907 × 4 = 0.010363 volume of KOH needed for titration = 0.010363 ÷ 0.267 = 0.0388 dm3 = 38.8 cm3 22 D no. of atoms in 50.0 cm3 of CO2 = 50.0 ÷ 24000 × 6.02 × 1023 × 3 = 3.76 × 1021 no. of atoms in 0.00750 moles of NO = 0.00750 × 6.02 × 1023 × 2 = 9.03 × 1021 no. of atoms in 0.45 g of SCl2 = 0.45 ÷ 103.1 × 6.02 × 1023 × 3 = 7.88 × 1021

no. of atoms in 2.35 × 1020 molecules of CH4 = 2.35 × 1020 × 5 = 1.18 × 1021 23 D colourless aqueous potassium sulfate is produced for option D. Neutralisation reaction does not produce a gas. 24 C NH4+ ions are absent as shown by the first test while NO3− ions are present as shown by the second test. 25 A CO32− ions are present as shown by the first test while either Pb2+ or Al3+ ions are present as shown by the second test. Since HCl is used and a colourless solution was produced, Pb2+ ions are eliminated since PbCl2 is insoluble in water. 26 C P must be a base since carbonates and metals would have reacted to produce a gas. Q must contain Cu 2+ ions because of the blue coloration. Cu2+ ions produce a blue precipitate which is insoluble in excess aqueous sodium hydroxide. 27 B A: True, since helium is used in balloons B: False, argon is used in light bulbs, not neon. Neon is used in advertising lights C: True, since noble gases are inert D: True 28 D A: Can be predicted since whether the oxide is metallic or non-metallic will give information about the basic or acidic nature of the oxide. B: Can be predicted since the number of valence electrons can be found from Group number, which in turn allows charge of ion to be predicted. C: Can be predicted using staircase line in Periodic Table D: Cannot be predicted 29 B S has a lower boiling point than R  S is higher in Group 17 than R S is darker in colour than Q  S is lower in Group 17 than Q R displaces P from its halide solution  R is higher in Group 17 than P From top to bottom: Q, S, R, P 30 C A: Incorrect since it is a chemical equation, not ionic equation B: Incorrect since it is not balanced C: Correct D: Incorrect since halogens should be diatomic

Paper 2 A1 Answers Marks (a)(i) H2SO4, MgO / Mg(OH)2 / MgCO3 / Mg (excess) [2] (a)(ii) Filtration [1] (a)(iii) Crystallisation [1] (b)(i) 250 [1] (b)(ii) Mr = 24.3 + 32.1 + 16.0 × 4 = 120.4 [1] (b)(iii) No. of moles = 2.41 ÷ 120.4 = 0.0200 [1] (b)(iv) Mass of water lost = 4.93 − 2.41 = 2.52 g No. of moles of water lost = 2.52 ÷ 18 = 0.140 n = 0.140 ÷ 0.0200 = 7 chemical formula of Epsom salt = MgSO4.7H2O [1] [1] [1] Total [10] A2 Answers Marks (a) Diffusion Diffusion occurs due to the random movement of particles OR Phenomenon occurs because particles tend to diffuse from a region of higher concentration to a region of lower concentration [1] [1] (bi) Substances A and B have the same Rf value of 0.20 in water/same solubility in water OR Substances B and C have the same Rf value of 0.40 in water/same solubility in ethanol. 2D chromatogra