2025 H1 Chem Prelim Paper 2 HCI

This document consists of 21 printed pages and 1 blank page. © Hwa Chong Institution 2025 8873/02/Prelim [Turn over HWA CHONG INSTITUTION C2 Preliminary Examination Higher 1 CANDIDATE NAME CT GROUP 24S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper Additional Materials: Data Booklet 8873/02 18 September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT group in the space provided at the top of this page. Write in dark blue or black pen. You may use a 2B pencil for any diagrams or graphs. Do not use staples, paper clips, glue, correction fluid or tapes. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. FOR EXAMINERS’ USE ONLY Paper 2 Section A 1 / 11 2 / 8 3 / 14 4 / 12 5 / 15 Section B 6 or 7 / 20 / 80 Paper 1 / 30 TOTAL / 100

2 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over Section A Answer all the questions in this section in the spaces provided. 1 (a) Table 1.1 lists the number of protons, neutrons and electrons in seven different particles. Each particle may be an atom, an anion or a cation. Table 1.1 particle number of protons number of neutrons number of electrons A 18 22 18 B 18 22 17 C 20 20 20 D 20 20 18 E 17 20 18 F 17 18 17 G 17 20 16 (i) Explain why particle E and particle F are a pair of isotopes of the same element. ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [1] (ii) State the number of electron pairs in particle G. …………………………………………………………………………..…….…………. [1] (iii) Identify the pair of atoms of different elements with the same nucleon number. …………………………………………………………………………..…….…………. [1] (iv) Explain why particle C is larger than particle D. ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [2]

3 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over (v) Deduce how the behaviour of beams of particles B, E and G, differ in an electric field. ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [2] (b) (i) Explain how the electronegativity of the elements in Period 3 influences the bonding in the chlorides. ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [1] (ii) Write equations to show what happens when water is added to a mixture of sodium chloride and phosphorus pentachloride. Suggest the expected pH of the resulting mixture. ………………………………………………………………………..………………….…... ………………………………………………………………………..……………….……... …………………………………………………………………….……………....…...… [3] [Total: 11]

4 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over 2 (a) State Le Chatelier’s Principle. .………………………………………………………………………………………………..…..... ……………………….………………………………………………………………………..…..... …………………………………….………………………………….………………............… [1] (b) A mixture of gaseous reactants and products was allowed to reach equilibrium. The effects on the equilibrium yield of the products caused by changes in the pressure and in the temperature of the gaseous mixture are shown in Fig. 2.1. Fig. 2.1 (i) Deduce whether the forward reaction is exothermic or endothermic. Explain your answer using references to Fig. 2.1 and to the equilibrium position. ………………………………………………………………………..………………….…... ………………………………………………………………………..………………….…... ………………………………………………………………………..……………….……... …………………………………………………………………….……………....…...… [2] . (ii) Deduce whether the forward reaction involves an increase or decrease in the total number of molecules in the gaseous mixture. Explain your answer using references to Fig. 2.1 and to the equilibrium position. ………………………………………………………………………..………………….…... ………………………………………………………………………..………………….…... ………………………………………………………………………..……………….……... …………………………………………………………………….……………....…...… [2]

5 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over (c) When steam is passed over white hot coke, hydrogen and carbon monoxide are produced. H2O(g) + C(s) H2(g) + CO(g) 2.0 moles of H₂O(g) and 3.0 moles of C(s) are placed in a 1 dm3 container and the mixture was allowed to reach equilibrium under certain conditions. The equilibrium mixture contains 0.30 moles of H₂(g). (i) Write the expression for the equilibrium constant, Kc, for this equilibrium. [1] (ii) Calculate the value of Kc under these conditions. [2] [Total: 8]

6 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over 3 Chlorofluorocarbons (CFCs) were widely used as refrigerants, aerosol propellants and industrial solvents until the mid-1980s. They are now banned in most countries because they lead to the depletion of the ozone layer. Two CFCs have the trade names Freon-11 and Freon-12. (a) (i) Give the IUPAC name of Freon-11. …………………………………………………………………………..……….………. [1] (ii) Another Freon has the formula CF4. Suggest the trade name of this Freon. …………………………………………………………………………..……….………. [1] (b) The shapes of the molecules of Freon-11 and Freon-12 are the same. Use VSEPR theory to describe and explain the shape of Freon-11. ………………………………………………………………………………………………..…..... ………………………………………………………………………………………………..…..... ………………………………………………………………………………………………..…..... ………………………………………………………………………………………………..…..... ……………………………………………………………………….………………............… [2] (c) State whether Freon-12 is a polar or non-polar molecule. Explain your answer. ………………………………………………………………………………………………..…..... ………………………………………………………………………………………………..…..... ……………………………………………………………………….………………............… [1]

7 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over (d) In the stratosphere, CFCs are broken down by ultraviolet radiation, releasing chlorine atoms. Equation 1 shows how chlorine atoms are produced from Freon-12. equation 1 CF2Cl2 → CF2Cl + Cl These chlorine atoms catalyse the breakdown of ozone in a two-step reaction. equation 2 Cl + O3→ ClO + O2 equation 3 ClO + O3→ 2O2 + Cl (i) Draw the ‘dot-and-cross’ diagram for a molecule of ozone, O3. [1] (ii) Use data from the Data Booklet to suggest why the ozone layer contains many more chlorine atoms than fluorine atoms. ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [1] (iii) Use equations 2 and 3 to write the overall equation for the breakdown of ozone. …………………………………………………………………………..……….………. [1] (iv) Explain, with the aid of a labelled Boltzmann distribution diagram, how chlorine atoms catalyse the breakdown of ozone. ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... ……………………………………………………………………………..……….………... …………………………………………………………………………..……….………. [2]

8 © Hwa Chong Institution 2025 8873/02/Prelim [Turn over (e) Researchers have converted Freon-11 into 3-dimensional graphene using molten magnesium at around 800 oC. Graphene is a single layer of carbon atoms. 3-dimensional graphene consists of layers of graphene stacked into a 3 -dimensiona