2025 JC2 Prelims H1 Chem Paper 2 QP TJC

8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS / 24 CENTRE NUMBER S INDEX NUMBER Chemistry 8873/02 Paper 2 Structured Questions 3 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, CG, centre and index number in the space provided at the top of this page. 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. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in bracket [ ] at the end of each question or part question. This document consists of 27 printed pages and 1 blank page. For Examiner’s Use Section A Q1 Q2 Q3 Q4 Q5 Section B Q6 /20 Q7 /20 Total /80

2 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section in the spaces provided. 1 Steel is an interstitial alloy, as carbon atoms fit in between iron atoms in the lattice. Brass is a substitution alloy, as zinc atoms replace the copper atoms in the lattice. Fig. 1.1 Stainless steel is a combination of interstitial and substitution alloys, because carbon atoms fit in between the lattice, but some of the iron atoms are replaced with nickel atoms. The structure of the alloy will determine properties such as hardness, which measures the material’s resistance to permanent shape change when a force is applied. These properties rely on how much electrostatic attraction is present between ions and electrons in any given volume of the lattice. The magnitude of the lattice strength can be measured using the formula below. Lattice Strength  q r + + (a) The ionic radius and ionic charge of the following ions with their respective chemical symbols are given in the following table. Table 1.1 Element C V Cr Fe Ni Cu Zn W Ionic radius (10-12 m) 15 64 62 55 56 73 74 66 Ionic charge +4 +3 +3 +3 +3 +2 +2 +4 (i) State which metallic element when added in small amount increase s the lattice strength of iron to the largest extent. Give a reason for your answer. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1] (ii) From the Table 1.1 above, suggest another element, other than nickel, that can be added to iron to form a substitutional alloy. ………………………………………………………………………………………………..[1]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over (iii) With the aid of a labelled diagram, describe the structure and bonding in iron. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[2] Metals are malleable because they can be hammered or pressed into shapes without breaking the metallic bond. The hardness of iron is enhanced when carbon atoms are added to iron atoms in the lattice. (iv) With reference to your answer in (a)(iii), explain how adding carbon atoms enhance the hardness of iron in steel. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1] (b) The melting points, in oC, of chlorides and iodides of two elements, iron and silicon, are shown below. Table 1.2 iron silicon chloride 677 -70 iodide 587 121 Explain, in terms of structure and bonding, the differences in melting points between FeC l2, SiCl4 and SiI4. …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... ………………………………………………………………………………………………………..[3] [Total: 8]

4 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 Hydrogen peroxide, H 2O2, finds its applications in a diversity of fields as it is considered an environmentally-friendly oxidising agent. (a) Suggest why it is environmentally-friendly to use H2O2 as an oxidising agent. …………………………………………………………………………………………………………... ………………………………………………………………………………………………………..[1] Today, most of the world’s hydrogen peroxide is manufactured by the anthraquinone process. This process involves the two steps shown below. step 1: O O + H2 OH OH Pd(s) catalyst Anthraquinone Anthrahydroquinone step 2: + O2 OH OH O O + H2O2 Anthrahydroquinone Anthraquinone

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over At the end of step 2, only anthraquinone and H 2O2 remain in the reaction mixture. H 2O2 can be separated out from the reaction mixture by adding water to the reaction mixture. (b) With reference to the interactions between relevant molecules, explain how the addition of water separates H2O2 from the reaction mixture. …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... ………………………………………………………………………………………………………..[2] (c) (i) Palladium metal is often used as a heterogeneous catalyst. Explain what is meant by a heterogeneous catalyst. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1]

6 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (ii) Explain how a heterogeneous catalyst increases the rate of reaction. Include a sketch of the Maxwell-Boltzmann distribution and use it to illustrate your answer. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[4] (d) It is observed that the catalytic activity of palladium is vastly increased when the catalyst is finely divided into nanoparticles. These nanoparticles are usually deposited onto the surface of inert metal particles such as gold. This prevents the nanoparticles from being a health hazard. (i) State the meaning of the term nanoparticles. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1] (ii) Explain why catalytic activity is vastly increased when nanoparticles of palladium are used. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1]

7 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over (iii) Predict how nanoparticles could present a risk to human health. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..