2025 RI H1Chem Prelims P2 Questions

RAFFLES INSTITUTION 2025 YEAR 6 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 8873/02 Paper 2 Structured Questions 16 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided at the top of this page. Write in dark blue or black pen. You may use a n HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 26 printed pages and 2 blank pages. For Examiner’s Use Section A 1 / 11 2 / 8 3 / 9 4 / 7 5 / 9 6 / 12 7 / 4 Section B (Please circle the question you have attempted) 8 / 20 9 / 20 Total / 80

2 © Raffles Institution 2025 8873/02/S/25 [Turn Over Section A Answer all the questions in this section in the spaces provided. 1 (a) Oxygen exists in various forms, including atoms, ions, and isotopes, each with distinct properties and applications. (i) Complete Table 1.1 for two species of oxygen. Table 1.1 species number of protons number of neutrons number of electrons electronic configuration 16 + 8O 8 1s2 16 2- 82O [2] (ii) Sketch an orbital in which the highest energy electron can be found in 16 + 8O . Label the orbital. [1]

3 © Raffles Institution 2025 8873/02/S/25 [Turn Over (b) The magnitude of angle of deflection for the path of a beam of O+ ions in an electric field is x. Add labelled lines to Fig. 1.1 to represent the paths of the beams of O+ and O22− ions in this electric field. + − Fig. 1.1 [1] Hence, state if the angle of deflection of O22− ions is greater, smaller or equal to x. …………………………………………………………………………………..………………[1] (c) The relative atomic mass of an element depends on the percentage abundance of each isotope present. A sample of oxygen atoms contains three isotopes, as shown in Table 1.2. Table 1.2 isotope relative isotopic mass percentage abundance / % 16O 15.994 99.76 17O 16.999 0.038 18O 17.999 0.202 Calculate the relative atomic mass of oxygen in this sample, giving your answers to two decimal places. [2] beam of O+ and O22− ions

4 © Raffles Institution 2025 8873/02/S/25 [Turn Over (d) Table 1.3 shows some properties of two ionic compounds. Table 1.3 ionic compound melting point / C lattice energy / kJ mol−1 MgO 2852 −3795 Ca(NO3)2 561 −1276 (i) Draw a ‘dot-and-cross’ diagram for Ca(NO3)2. [2] (ii) Explain why the magnitude of lattice energy of MgO is much higher than that of Ca(NO3)2. ……………………………………………………………………………………..……… ……………………………………………………………………………………..……… ……………………………………………………………………………………..……… ……………………………………………………………………………………..……… ……………………………………………………………………………………………[2] [Total: 11]

5 © Raffles Institution 2025 8873/02/S/25 [Turn Over BLANK PAGE

6 © Raffles Institution 2025 8873/02/S/25 [Turn Over 2 Many industries produce wastewater containing heavy metal ions such as dichromate ions that must be removed before the water is released into the environment. This can be done by carrying out a three-step process. step 1: An acidified iron(II)-containing solution was added in excess to a wastewater sample containing dichromate ions, Cr2O72–, to form chromium(III) ions, Cr3+. step 2: To the same sample, hydroxide ions, OH −, was added to fully precipitate Cr 3+ as chromium(III) hydroxide, Cr(OH)3(s). step 3: The mixture was filtered to remove Cr(OH)3(s). (a) Define the term mole. ……………………………………………………………………………………..……………….. …………………………………………………………………………………..………………..[1] (b) Write half−equations to show the oxidatio n and reduction for the reaction between Fe 2+ and Cr2O72–, in acidic medium. Hence , write the overall ionic equation for the reaction . oxidation ……………………………………………………………………………………..……. reduction ……………………………………………………………………………..……………. overall …………………………………………………………………………………..…………. [2]

7 © Raffles Institution 2025 8873/02/S/25 [Turn Over (c) 30.00 cm3 of wastewater from a factory and 20.0 cm3 of excess acidified iron(II)-containing solution were added to a 250 cm3 volumetric flask. Deionised water was added so that the total volume of the solution was 250 cm3. This solution was labelled Y. 25.0 cm3 of solution Y was reacted with a hydroxide solution to give 0.0588 g of Cr(OH)3. (i) Calculate the amount of Cr(OH)3 in the dry sample. [1] (ii) Calculate the amount of Cr2O72– present in 30.00 cm3 of wastewater. [2] (iii) Hence, calculate the minimum concentration of Fe2+ in the iron(II)-containing solution needed for the complete reduction of Cr2O72– to Cr3+. [2] [Total: 8]

8 © Raffles Institution 2025 8873/02/S/25 [Turn Over 3 (a) Cellulose is one of the most abundant linear polymers found in nature. Besides wood and paper, cellulose can also be found in fabrics such as cotton. (i) Define the term polymer. ……………………………………………………………………………………..………… …………………………………………………………………………………..…………[1] (ii) Cellulose polymer is formed by the following reaction. State the class of polymers for cellulose. ……………………………………………………………………………………………..[1] (iii) Fig. 3.1 shows two linear cellulose polymer chains. Fig. 3.1 With reference to Fig. 3.1, suggest the type of bonding represented by the dotted lines. …………………………………………………………………………………………….. [1] (iv) Hence, explain why a new cotton shirt tends to crease when it is washed and dried. ……………………………………………………………………………………..…........... ……………………………………………………………………………………..…........... ……………………………………………………………………………………..…........... ………………………………………………………………………………………….….[2]

9 © Raffles Institution 2025 8873/02/S/25 [Turn Over (b) The structure of compound A, C5H10O, is shown. A (i) Explain why A is able to exist as cis and trans isomers. ……………………………………………………………………………………..…........... ……………………………………………………………………………………..…........... …………………………………………………………………………………………….. [2] (ii) B is an isomer of A. B contains a C=C but cannot exist as cis-trans isomers. B reacts with acidified K2Cr2O7 to form a ketone. Draw the structure of B. [1] (iii) C is another isomer of A, and the structure of C is