FHSS Chem Prelim P2

Candidate Name: Class: Index No.: FUHUA SECONDARY SCHOOL Secondary Four Express PRELIMINARY EXAMINATION 2025 4E Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Seco ndary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Seco ndary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Seco ndary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Seco ndary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Secondary School Fuhua Seco ndary School CHEMISTRY 6092/2 Paper 2 DATE 22 August 2025 TIME 1045 - 1230 DURATION 1 hour 45 minutes READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided. Section B 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 24. The use of an approved scientific calculator is expected, where appropriate. PARENT’S SIGNATURE FOR EXAMINER’S USE Section A Section B Total /70 /10 /80 This document consists of 23 printed pages and 1 blank page.

2 Section A Answer all questions. 1 Fig. 1.1 shows the electron arrangement of six elements from Period 3 of the Periodic Table. The elements are represented by the letters, A, B, C, D, E and F. Each diagram shows outer electrons only. A B C D E F Fig. 1.1 (a) Which elements are reducing agents? [1] (b) Which elements form oxides that react with aqueous sodium hydroxide only? [1] (c) Which element exists as a giant network of atoms that are covalently bonded? [1] (d) Draw a ‘dot-and-cross’ diagram to show the bonding of the compound formed between element B and D. [2] [Total: 5]

3 2 Sulfuric acid, widely used in the production of detergents and fertilisers, is manufactured on an industrial scale via the Contact Process. The process involves the following key reactions as shown in Table 2.1. Table 2.1 stage reaction conditions 1 S (s) + O2 (g) → SO2 (g) ΔH = - 297 kJ/mol 2 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) 450 °C 1- 2 atm V2O5 as catalyst H = - 196 kJ/mol 3 SO3 (g) + H2SO4 (l) → H2S2O7 (l) Heat produced varies. 4 H2S2O7 (l) + H2O (l) → 2H2SO4 (aq) Heat produced varies. (a) A student made the following comment. ‘In stage 2, the catalyst reduces the activation energy for the reaction and therefore the enthalpy change of the reaction is lower.’ Do you agree with this statement. Explain why. [2] (b) Explain, in terms of oxidation state, which stage(s) involve(s) redox reactions. [3] (c) The percentage yield to produce sulfuric acid from sulfur is only 96 – 98%. Using the information in Table 2.1, explain why. [1]

4 (d) (i) Draw an energy profile diagram for the backward reaction in stage 2 of the contact process. 2SO3 (g) → 2SO2 (g) + O2 (g) Label clearly the • reactants and products, • enthalpy change and • activation energy of the reaction. [2] (ii) Calculate the total amount of heat produced from stage 2 when 50 kg of SO 3 is produced. [2] [Total: 10] energy progress of reaction

5 3 (a) A student investigated the electrolysis of concentrated aqueous potassium chloride using the set-up as shown in Fig. 3.1. Fig. 3.1 (i) Construct the half-equation, with state symbols, for the reaction at electrode P. [1] (ii) Describe and explain what you will observe in the beaker containing aqueous sodium bromide as the electrolysis experiment proceeds. [3] (iii) The student conducted a second experiment. Dilute copper (II) chloride was used instead of concentrated potassium chloride . Predict and explain the expected observations in the gas syringe and beaker containing aqueous sodium bromide. [3]

6 (b) Fig. 3.2 shows a set-up to electroplate an object with silver. cell 1 cell 2 Fig. 3.2 (i) On Fig. 3.2, indicate the direction of electron flow. [1] (ii) A student would like to coat his metal toy car with silver. In which electrode, 1, 2, 3 or 4, should he place his toy car? With the help of a half-equation, explain your answer. [2] (iii) Describe and explain how the pH of the electrolyte in cell 2 changes during the experiment. [2] [Total: 12]

7 4 Fig. 4.1 shows the setup with two tubes, 1 and 2, to investigate the rate of diffusion of gases. Two pieces of cotton wool soaked in fluorine and chlorine solution were placed in one end of tubes 1 and 2 respectively. The solution on the filter papers of both tubes turned brown. Fig. 4.1 Table 4.1 shows the time taken for the gases to diffuse and for the solution on the filter paper to turn brown. Table 4.1 gas Mr time taken / s fluorine, F2 16 chlorine, Cl2 29 (a) Complete Table 4.1 by filling in the Mr for each gas. [1] (b) Construct an ionic equation for the reaction in tube 1. [1] (c) A student makes this conclusion: 'The rate of diffusion is directly proportional to the relative molecular mass of each gas.' Do the measurements obtained in the experiment support this conclusion? Explain your reasoning. [2] [Total: 4]

8 5 (a) Table 5.1 gives the structures of four organic substances, A, B, C and D. Table 5.1 A B C D (i) Substance B can be synthesised from substance A in two consecutive reaction steps. Write the chemical equation for each step involved, showing displayed formulae of all organic substances. step 1: step 2: [3] (ii) State the names of the two organic substances that react to form C. [1]

9 (iii) The labels of the four solutions, A, B, C and D have been misplaced. A chemist must conduct chemical tests to distinguish and identify each solution. Describe chemical tests the chemist could conduct to identify each of the four solutions in a sequential manner. [3] (b) Used cooking oil being processed to produce biodiesel has gained a significant amount of consideration within the world of fuel production. During the conversion process, fatty acid triglycerides in vegetable oil react with methanol, in presence of an alkali catalyst, to produce biodiesel. Biodiesels are fatty acid methyl esters (FAME), which has similar properties to petrol diesel. The by -product of this reaction is glycerol, a tri-ol, which is extracted and used for other products including soaps and cosmetics. The structure of triglycerides and FAME are fatty acid triglycerides FAME where R is a hydrocarbon chain. (i) One mole of fatty acid triglyceride reacts with 3 moles of methanol to produce FAME and glycerol. Construct a chemical equation for this reaction. Show the structural formulae of the organic molecules. [2]

10 (ii) Suggest why glycerol is known as a tri-ol. [1] (iii)