2020 SAJC H2 Prelim Paper 1 (QP)

1 [Turn over CANDIDATE NAME CLASS 19S ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examination CHEMISTRY Paper 1 Multiple Choice 9729/01 September 2020 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name and class on the Answer Sheet in the spaces provided. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer sheet. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 18 printed pages.

2 [Turn over 1 Carbon disulfide, CS2, burns in oxygen according to the following equation. CS2(g) + 3O2(g)  CO2(g) + 2SO2(g) 10 cm3 of carbon disulfide was completely burnt in 50 cm3 of oxygen. The resulting mixture was then treated with excess of aqueous sodium hydroxide. All measurements of volume were made at the same temperature and pressure in which all the reactants and products were in the gaseous state. What was the volume of the gas after burning and after adding NaOH(aq)? volume of gas after burning / cm3 volume of gas after adding NaOH(aq) / cm3 A 30 10 B 30 20 C 50 20 D 50 40 2 1 mole of X2O32− oxidised 68.1 dm3 of sulfur dioxide gas to sulfate ions at standard temperature and pressure. What is the final oxidation state of X? A −2 B −1 C +1 D +2

3 [Turn over 3 Use of the Data Booklet is relevant to this question. Which species have the same number of unpaired electrons as chlorine atom? 1 Li+ 2 Mg+ 3 O− 4 F− A 2 and 3 B 3 and 4 C 1 only D 2 only 4 Hospitals require large amount of oxygen gas in the treatment of patients with respiratory symptoms. Oxygen is liquefied under pressure and stored in special cylinders. It vapourises when pressure is released. Which statement best describes why oxygen gas liquefies under pressure? A High pressure lowers the kinetic energy of oxygen molecules, creating less disordered liquid state. B High pressure pushes the molecules closer for more effective intermolecular interactions. C High pressure causes the temperature of oxygen gas to increase above its boiling point. D High pressure decreases the total volume occupied by the oxygen molecules.

4 [Turn over 5 Which species contain a dative (co-ordinate) bond? 1 CO 2 CO32− 3 N2H4 4 N2O4 A 2, 3 and 4 B 1 and 2 only C 1 and 4 only D 3 and 4 only 6 One proposed strategy to reduce the amount of greenhouse gases in the atmosphere is to capture carbon dioxide emissions from fossil fuel power plants and pump them into the deep ocean bed. Under the extreme high pressure of the deep ocean bed, carbon dioxide would dissolve in water and stay out of the atmosphere. CO2(g) + nH2O(l) ⇌ CO2.nH2O(aq) What will be the signs of H and S for the forward reaction of this equilibrium at the deep ocean bed? H S A   B  + C +  D + +

5 [Turn over 7 The table shows the charge and radius of each of six ions. ion J+ L+ M2+ X− Y− Z2− radius / nm 0.14 0.18 0.16 0.14 0.18 0.16 The ionic solids JX, LY and MZ are of the same lattice type. What is the correct order of their lattice energies, placing the least exothermic first? A JX, LY , MZ B JX, MZ, LY C LY, JX, MZ D LY, MZ, JX 8 Ammonium nitrate is commonly used in making of fertilisers. 2NH4NO3(s)  2N2(g) + 4H2O(g) + O2(g) The decomposition of ammonium nitrate at 230oC give gases. It is a first-order reaction with a half-life of 10 min. Explosion happens when the molar proportion of ammonium nitrate to gases is 1:14. How long would it take for ammonium nitrate to explode at 230oC? A 23 min B 35 min C 70 min D 80 min

6 [Turn over 9 The reaction of nitrogen monoxide and hydrogen gas, 2NO(g) + 2H2(g) N2(g) + 2H2O(g) involves the following steps: I NO + NO N2O2 (fast) II N2O2 + H2 H2O + N2O (slow) III N2O + H2 N2 + H2O (fast) Which statements about the reaction are correct? 1 N2O acts as the catalyst. 2 The reaction is second order with respect to [NO]. 3 The units of the rate constant is mol−3 dm9 s−1. 4 When partial pressure of H2 doubles, rate of reaction quadruples. A 1, 2 and 3 B 1 and 3 only C 2 and 4 only D 2 only 10 Given that the Kp for the following equilibrium is 125 at 65oC, X(s) + 3Y(g) ⇌ 3Z(g) What is the mole ratio of Y : Z at equilibrium at 65oC? A 1 : 1 B 1 : 5 C 25 : 1 D 125 : 1

7 [Turn over 11 Boric acid, B(OH) 3, is often used as an antiseptic and as a precursor to other chemical compounds. The following equilibrium illustrates the acidity of boric acid. B(OH)3(aq) + 2H2O(l) B(OH)4−(aq) + H3O+(aq) Ka = 7.3×10−10 NaB(OH)4 is a weak base. What is the pH of 0.20 mol dm−3 NaB(OH)4(aq)? A 9.1 B 9.4 C 11.2 D 13.3 12 Human plasma is buffered mainly by dissolved CO2, which reacts to form carbonic acid, H2CO3. H2CO3(aq) H+(aq) + HCO3−(aq) Given that the pH of human plasma is 7.4 and the acid dissociation constant, Ka, of carbonic acid is 8 x 10−7 mol dm−3, which statements are correct? 1 The ratio of [HCO3−] to [H2CO3] in human plasma is 20 : 1. 2 The human plasma has a maximum buffer capacity at around pH 6. 3 This buffer system is more efficient in removing acid than base. 4 This buffer system can be prepared by mixing suitable amounts of sodium hydrogencarbonate and sodium hydroxide. A 1, 2 and 3 B 1 and 3 only C 2 and 4 only D 3 only

8 [Turn over 13 Values of two solubility products of copper carbonate, CuCO 3, and neodymium carbonate, Nd2(CO3)3 are given. Ksp (CuCO3) = 1 x 10−10 mol2 dm−6 Ksp (Nd2(CO3)3) = 1 x 10−33 mol5 dm−15 Solid copper carbonate is shaken with water. The remaining solid is filtered off, leaving a saturated solution X. Drops of dilute aqueous neodymium nitrate are added to X until neodymium carbonate just precipitates. Which row of the table is correct? [CO32−] in X / mol dm–3 [Nd3+(aq)] when Nd2(CO3)3 just precipitates / mol dm–3 A 1 x 10−5 1 x 10–9 B 1 x 10−5 1 x 10–18 C 5 x 10−11 8 x 10−3 D 5 x 10−11 9 x 10–2 14 Which statement about Period 3 elements and their oxides is false? A The resultant pH of the oxides in water decrease across the period. B The melting points of elements decrease across the period. C The covalent character of oxides increase across the period. D The maximum oxidation state of elements increases across the period. 15 Which property generally increases down Group 2? A sum of the first and second ionisation energies B reactivity of metal with cold water C polarising power of the cation D oxidising power of the cation

9 [Turn over 16 X2, Y2 and Z2 are bromine, chlorine and iodine but not necessarily in the order given while X−, Y− and Z− are their corresponding halide ions. The table below shows the observations of two experiments involving the addition of these halogens to separate aqueous solutions containing the halide ions , followed by the addition of an organic solvent. Experiment Reactions Observations 1 X2 (aq) + Y− (aq) violet organic layer 2 Z2 (aq) + X− (aq) violet organic layer Which statement is correct? A Reaction of X2(aq) with Z−(aq) would produce a different observation from experiments 1 and 2. B Displacement took place in both experiments 1 and 2. C X− is a weaker reducing agent than both Y− and Z−. D H-X bond is weaker than H-Y and H-Z bond.

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