2024 CGS Chemistry Prelim P2

Page 1 of 23 CRESCENT GIRLS’ SCHOOL SECONDARY FOUR PRELIMINARY EXAMINATION 2024 Paper 2 READ THESE INSTRUCTIONS FIRST Candidates answer on the Question Paper. No Additional Materials are required. Write your name, register number and class in the spaces provided at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph. Do not use staples, paper clips, and glue or correction fluid. Section A (70 Marks) Answer all questions Write your answers in the spaces provided. Section B (10 Marks) Answer one question. Write your answers in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 23. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A Section B Deductions Significant Figures Units Total 80 This paper consists of 23 printed pages including cover page. CHEMISTRY Class: Register No: Name: 6092/02 23 August 2024 1 hr 45 mins

Page 2 of 23 Section A Answer all questions in this section in the spaces provided. The total mark for this section is 70. A1 The figure below shows ‘dot-and-cross’ diagrams for molecules that contain elements from the first two periods of the Periodic Table. The elements are represented by the letters M, Q, R, T and Z. Each diagram shows outer electrons only. Use the letters M, Q, R, T and Z to answer the questions below. (a) Which element can form an ion with a charge of 1-? [1] (b) Which element can lose, gain and share electrons? [1] (c) Which element can form an acidic oxide? [1] (d) Which element forms a triple covalent bond? [1]

Page 3 of 23 (e) (i) Potassium reacts with element T to form a compound. Draw a dot-and-cross diagram of the compound formed between potassium and element T. Show only the valence electrons. [2] (ii) State one physical property of the above compound and explain the reason for the physical property. [2] [Total: 8 marks]

Page 4 of 23 A2 The table below shows information about the preparation of pure samples of some solid salts. Complete the table by filling in the missing information. Include state symbols with the formulae. formulae of salt formulae of reagent 1 formulae of reagent 2 method of preparation CaCO3 (s) _________________ Ag2SO4 (s) H2SO4 (aq) Adding excess solid to acid evaporation and crystallisation NH4NO3 (s) HNO3 (aq) _________________ evaporation and crystallisation [5] [Total: 5 marks] A3 Nitrogen dioxide is an acidic oxide. It dissolves in water to form two acids, nitric acid and nitrous acid, HNO2 in a single reaction. (a) (i) Write a balanced chemical equation for the above reaction. [1] (ii) Disproportionation is a reaction when the same substance is oxidised and reduced in the same reaction. Explain why the reaction in (a)(i) is a disproportionation reaction. [2]

Page 5 of 23 (b) One of the main sources of nitrogen monoxide, NO is from the combustion engines of vehicles. (i) State how nitrogen monoxide, NO is formed in combustion engines of vehicles. [2] (ii) Hence, explain with the aid of a chemical equation how nitrogen monoxide is removed by catalytic converters fitted in cars. [2] The amount of air in the pollutant gases that enter the catalytic converter affects the reactions in the converter. The graph shows the percentage of nitrogen monoxide that the catalytic converter successfully removed. (iii) Using the equation in (ii) and the graph above, explain why the percentage of nitrogen monoxide successfully removed by catalytic converter decreases as the amount of air increases. [2] [Total: 9 marks]

Page 6 of 23 A4 A student electrolysed aqueous copper(II) sulfate using two sets-ups shown below. The electrodes used in each set-up are made of the same material. However, the electrodes used in set-ups A and B are made of different materials. He recorded the following observations in the two set-ups. set-up A set-up B mass of electrode A1 increased mass of electrode B1 increased mass of electrode A2 remained the same mass of electrode B2 decreased effervescence observed at electrode A2 blue copper(II) sulfate solution fades in colour. no effervescence observed at B2. blue copper(II) sulfate solution remains unchanged. (a) Name the particles which transfer charges through the: [1] (i) copper wires ______________________________ (ii) copper(II) sulfate solution ______________________________ (b) State which electrode is the cathode in each set-up. Set-up A: _______________ Set-up B: _______________ [1] (c) Explain, with an appropriate equation, the increase in mass at electrodes at A1 and B1. [2] set-up A set-up B copper wires Power supply Power supply copper(II) sulfate solution copper(II) sulfate solution

Page 7 of 23 (d) Write the half-equations of the reactions taking place at Electrode A2 and Electrode B2. [2] Half-equation at A2: ________________________________________ Half-equation at B2: ________________________________________ (e) Describe how the electrolyte of set-up A would change by the end of experiment in terms of its pH and explain why. [2] (f) Suggest the materials that are used to make the electrodes in: [1] (i) Set-up A: ____________________ (ii) Set-up B: ____________________ [Total: 9 marks] A5 The table below shows four different experiments that were conducted with various concentrations and volumes of three different acids that reacted with excess zinc. experiment acid concentration of acid in mol/dm3 Volume of acid in cm3 1 hydrochloric acid 0.10 100 2 hydrochloric acid 0.20 100 3 ethanoic acid 0.10 100 4 sulfuric acid M N (a) The chemical equation between zinc and hydrochloric acid is shown below. Zn + 2HCl → ZnCl2 + H2 (i) Find the number of moles of hydrochloric acid that reacted in Experiment 1. [1]

Page 8 of 23 (ii) Hence, find the volume of gas that is evolved in Experiment 1. [2] (iii) The graph below shows the graph for Experiment 1. Hence, sketch the graph for Experiment 2 and label it as Expt 2. [1] (b) (i) Write an equation to show the chemical reaction between ethanoic acid and zinc. [1] (ii) Hence, sketch the graph for Experiment 3 in the same axes in (a)(iii) and label it as Expt 3. [2] Volume of gas/cm3 Time/s Expt 1

Page 9 of 23 (iii) Explain the shape of your graph. [3] (c) Suggest values for M and N in the table above so that Experiment 4 can have the same graph as Experiment 2. [2] M: ____________________ N: ____________________ [Total: 12 marks] A6 Zinc is a transition metal found in Period 4 of the Periodic Table. Some properties of zinc are shown in the table below. zinc electronic configuration 2.8.18.2 melting point/⁰C 419 density/ g/dm3 2.99 formula of metal oxide ZnO