Compassvale Sec 4 Exp Prelim Chem P2 2025 QP

[Turn over COMPASSVALE SECONDARY SCHOOL Secondary Four Express Preliminary Examination 2025 NAME CENTRE NUMBER S CLASS INDEX NUMBER ___________________________________________________________________________ CHEMISTRY 6092/02 Paper 2 20 August 2025 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, class, index number and name 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 21. The use of an approved scientific calculator is expected, where appropriate. __________________________________________________________________________ This document consists of 21 printed pages and 1 blank page. Set by: Mdm C Lim

2 Section A Answer all questions. 1 This question is about making salts. For each salt, suggest the name of the missing reagent and briefly describe how to obtain the solid salt from the reaction mixture. salt barium sulfate copper(II) nitrate reagent 1 aqueous barium nitrate dilute nitric acid reagent 2 description on how to obtain solid salt from reaction mixture [6] [Total:6] 2 A sample of chlorine gas is placed in a gas syringe. It is connected to a glass tube that contains aqueous sodium bromide absorbed in cotton wool as shown in Fig. 2.1. . Fig. 2.1 The chlorine gas was passed over the cotton wool into the other syringe and then back again a few times until there was no further change in the volume. (a) (i) Predict what you would expect to observe at the cotton wool. ………………………………………………………………………………………………. [1] chlorine gas aqueous sodium bromide absorbed in cotton wool

[Turn over 3 (ii) Explain, with the aid of an ionic equation, the observation in (a)(i). ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. [2] (b) Suggest another sodium salt that can be used in this experiment. ……………………………………………………………………………………………………… [1] [Total:4] 3 Boric acid, H3BO3, is an ingredient often found in eye wash products due to its mild antiseptic properties that can help inhibit the growth of bacteria. The pH values of two separate samples of 0.05 mol/dm3 boric acid and hydrochloric acid were taken using a data logger. The results are shown in Table 3.1. Table 3.1 acid pH boric acid 5.25 hydrochloric acid 1.30 (a) Boric acid is also known as hydrogen borate. Deduce the formula for borate ion. ……………………………………………………………………………………………………… [1] (b) Use Table 3.1 to explain why boric acid has a higher pH than hydrochloric acid. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2]

4 (c) Subsequently, these two samples of acids were each added in excess to 0.02 g of zinc granules separately. (i) Effervescence was observed during the experiment and a gas was evolved. Describe a test to identify the gas evolved. test ………………………………………………………………………………………….. observation ………………….…………………………………………………………….. ………………………………………………………………………………………………. [2] (ii) For both reactions, the mole ratio of zinc to gas evolved is the same. A statement was made about both reactions: ‘The final volume of gas produced in the reaction of zinc and boric acid would be less than the reaction of zinc and hydrochloric acid as it is a weaker acid.’ Do you agree with this statement? Explain your reasoning. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. [2] [Total:7]

[Turn over 5 4 Four amino acids P, Q, R and S were analysed using paper chromatography. Two solvents were used. Table 4.1 shows the Rf values calculated for the four amino acids. Table 4.1 amino acid P Q R S Rf in solvent 1 0.30 0.00 0.60 0.90 Rf in solvent 2 0.60 0.52 0.25 0.85 (a) Amino acids are colourless. Describe and explain how the amino acids can be analysed using paper chromatography. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [1] (b) Which amino acid is the most soluble in both solvents? Explain your choice. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2] (c) Which solvent is a better solvent to analyse these four amino acids? Use information from Table 4.1 to explain your reasoning. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2] [Total:5]

6 5 Petrol is used as a fuel in cars. Petrol contains mainly octane, C8H18. Two other alternative fuels for cars are propane and ethanol. Table 5.1 shows some information about the various fuels used in cars. Table 5.1 fuel boiling point / °C density at room temperature and pressure in g/dm3 volume of 1 mol of fuel at room temperature and pressure / dm3 enthalpy change of combustion / kJ per mol enthalpy change of combustion / kJ per kg octane 125 703 –5075 –44 518 propane –42 1.81 24.3 –2220 –50 455 ethanol 78 789 0.0583 –1367 . (a) Calculate the volume of 1 mol of octane and the enthalpy change of combustion in kJ per kg for ethanol. Show your workings clearly. [3]

[Turn over 7 (b) Use the information in the table to evaluate the use of propane and ethanol as fuels. Your answer should consider: • the ease of storage, • the energy content of the fuels, • the source of fuels. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [3] (c) Complete the energy profile diagram for the complete combustion of ethanol. Your diagram should include: • the chemical formulae of the reactants and products, • the enthalpy change of reaction, ΔH • the activation energy, Ea. [3] (d) The burning of fuels in cars contribute to the amount of carbon dioxide in the atmosphere. Briefly describe a process in the carbon cycle that helps to regulate the amount of carbon dioxide in the atmosphere. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [1] [Total:10] energy progress of reaction

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