2025 AMKSS Prelim P2 QP

[Turn Over Candidate NameForm Class Index Number ANG MO KIO SECONDARY SCHOOLPRELIMINARY EXAMINATION 2025SECONDARY FOUR EXPRESSCHEMISTRY6092/02Paper 229 August 20251 hour 45 minutesSetter: Mr Vincent VooCandidates answer on the Question Paper.No Additional Materials are required.READ THESE INSTRUCTIONS FIRSTWrite your name, class and index number in the spaces provided at the top of this paper.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.

2 AMKSS 4E Prelim Exam6092/02/2025 Section AAnswer all questions.1Table 1.1 shows the atomic structure of six particles, represented by the letters P to U. These particles are either atoms or ions, and the letters are not the symbols of the elements.Table 1.1particlesnumber of electronsnumber of protonsnumber of neutronsP121212Q222R666S101212T668U7714Use the letters, P to U to answer the following questions.(a)Which two particles are an atom and an ion of the same element?…………………………………………………………………………………………….[1](b)Which particle is chemically unreactive?…………………………………………………………………………………………….[1](c)Write the formula of the compound formed between particles P and U.…………………………………………………………………………………………….[1](d)Draw the electronic structure of particle S by showing all electrons.[1][Total: 4]

3 AMKSS 4E Prelim Exam6092/02/2025[Turn Over 2Substance X is formed by burning phosphorus in a limited supply of oxygen gas. Fig. 2.1 shows the structure of substance X. (a)What type of bonding is present in substance X? Explain your answer.…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[2](b)Write the chemical formula of substance X.…………………………………………………………………………………………….[1](c)Substance X forms a liquid when heated to 23.8 oC. In terms of its structure, predict and explain the electrical conductivity of pure liquid X.…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[2]

4 AMKSS 4E Prelim Exam6092/02/2025 (d)Substance X reacts with water to form a colourless solution Y. With reference to the pH of water, predict and explain the pH of solution Y.…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[2][Total: 7]3Table 3.1 shows the bond energies of some bonds.Table 3.1bondbond energy (kJ/mol)C − Cl339C − H413H − Cl431C − F495C = C610Chlorodifluoromethane is used to make tetrafluoroethene as shown by the equation. (a)Calculate the energy change involved in bond breaking.energy change in bond breaking = ……………………. kJ[2]

5 AMKSS 4E Prelim Exam6092/02/2025[Turn Over (b)Calculate the energy change involved in bond making.energy change in bond making = ……………………. kJ[2](c)Hence, calculate the enthalpy change for the reaction.enthalpy change = ……………………. kJ[1](d)Explain why the bond energy of the C − F bond is more than the bond energy of the C – Cl bond.……………………………………………………………………………………………..……………………………………………………………………………………………..……………………………………………………………………………………………..[1][Total: 6] 4Air bags are used to protect passengers in a car during an accident. When the crash

6 AMKSS 4E Prelim Exam6092/02/2025 sensor detects an impact, it causes a mixture of chemicals to be heated to a high temperature to react to produce nitrogen gas. The nitrogen gas fills the air bag as shown in Fig. 4.1. The mixture of chemicals in the air bag contains sodium azide, potassium nitrate and silicon dioxide. Sodium azide, NaN3 decomposes on heating to form sodium and nitrogen. The mass of sodium azide in an air bag typically ranges from 50 g to 150 g, depending on the air bag’s size and design.(a)Write the equation, without state symbols, for the decomposition of sodium azide.…………………………………………………………………………………………….[1](b)Calculate the volume of nitrogen produced at room temperature and pressure if an air bag contains 120 g of sodium azide. [3](c)Potassium nitrate and silicon dioxide are found in the mixture of chemicals in the air bag to help make the sodium produced from the decomposition of sodium azide safe.

7 AMKSS 4E Prelim Exam6092/02/2025[Turn Over Sodium reacts with potassium nitrate to form sodium oxide, potassium oxide and nitrogen.(i)Write the equation, without state symbols, for the reaction between sodium and potassium nitrate.……………………………………………………………………………………..[1](ii)Suggest why there is a need to make the sodium produced safe.……………………………………………………………………………………..……………………………………………………………………………………..[1](d)The salt potassium nitrate can be prepared in the laboratory. Suggest the method and the formulae of the reagents used.method: …………………………………………………………………………………...formulae of the reagents: ………………………………………………………………[2][Total: 8]5Table 5.1 shows the formulae of some chemical reagents commonly found in the laboratory. Table 5.1Zn (s)Ag (s)Na2CO3 (aq)Cu(NO3)2 (aq)(NH4)2SO4 (aq)NaOH (aq)HNO3 (aq)BaCO3 (s)KI (aq)Ag(NO3)2 (aq)Use the formulae to answer the following questions. You may use each formula once, more than once or not at all.Write down the formulae of any two reagents, which when mixed together(a)would produce a gas with a pH value of 12.……………………………………………………………………………………………..[1](b)would produce a gas that extinguishes a lighted splint with a ‘pop’ sound.……………………………………………………………………………………………..[1]

8 AMKSS 4E Prelim Exam6092/02/2025 (c)would produce a green insoluble salt.……………………………………………………………………………………………..[1](d)would produce a red brown solid.……………………………………………………………………………………………..[1](e)would produce a yellow precipitate.……………………………………………………………………………………………..[1][Total: 5]6 Fig. 6.1 shows the set-up of two electrolytic cells. The four electrodes, A, B, C and D are made of graphite. The switch is turned on once the electrolysis experiment begins.(a)With reference to Fig. 6.1, explain why there is no current flow when the switch is turned on. …………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[2](b)Suggest what can be done to the set-up in Fig. 6.1 for the electrolysis experiment to begin.…………………………………………………………………………………………….

9 AMKSS 4E Prelim Exam6092/02/2025[Turn Over …………………………………………………………………………………………….[1]For questions (c) to (e), it is assumed that the experimental error in the set-up has been rectified.(c)Describe and explain, with the aid of an equation, the observation made at electrode A.…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[3](d)Describe and explain, with the aid of an equation, the observation made at electrode B.…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….…………………………………………………………………………………………….[3](e)What observation would be made of the copper(II) sulfate electrolyte after electrolysis has been carried out for some time?…………………………………………………………………………………………….…………………………………………………………………………………………….[1][Total: 10]7Crude oil is a mixture of mostly alkanes.Table 7.1 shows the names and formulae of some alkanes.

10 AMKSS 4E Prelim Exam6092/02/2025 Table 7.1alkaneformulapropaneC3H8butaneC4H10octanehexadecaneC16H34(a)State the separation technique used to separate crude oil into useful products.…………………………………………………………………………………………….[1](b)One molecule of octane contains 8 carbon atoms. Write the molecular formula of octane.…………………………………………………………………………………………….[1](c)Describe and ex