2025 DHS H1 Chem Prelim Paper 2_Suggested Solutions

© DHS 2025 8873/02 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H1 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 centre number, index number, name and class 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. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 11 2 9 3 11 4 10 5 14 6 5 Section B 7 / 8 20 Total 80 This document consists of 23 printed pages.

2 © DHS 2025 8873/02 Section A Answer all the questions in the spaces provided. 1 (a) Use of the Data Booklet is relevant to this question. Chlorine has 25 isotopes, ranging from 28Cl to 52Cl. (i) Complete Table 1.1 to show the number of each sub-atomic particle present in an 39Cl+ ion. Table 1.1 number of protons number of electrons number of neutrons 39Cl+ 17 16 22 [1] A sample of chlorine contains three isotopes. Data for two of the isotopes present in this sample is shown in Table 1.2. Table 1.2 mass number abundance 35 68.43% 37 21.70% The sample of chlorine has a relative atomic mass, Ar, of 35.53. (ii) Calculate the mass number of the third isotope. [2] Abundance of the third isotope = 100% – 68.43% – 21.70% = 9.87% Let the mass number of the third isotope be x. 35.53 = (35 × 68.43 100 ) + (37 × 21.70 100 ) + (𝑥 × 9.87 100) 𝑥 = 35.97 ≈ 𝟑𝟔 (𝑛𝑒𝑎𝑟𝑒𝑠𝑡 𝑤ℎ𝑜𝑙𝑒 𝑛𝑢𝑚𝑏𝑒𝑟) A beam of 35Cl+ ions is deflected in an electric field. (iii) State one similarity and one difference in the expected behaviour of a beam of 35Cl– ions in the same electric field. Briefly explain your answer. [2] Similarity: The angle of deflection of both beams are of the same magnitude. This is because both ions have the same | 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑎𝑠𝑠 | ratio.

3 © DHS 2025 8873/02 [Turn over Difference: The beams are deflected to opposite directions. The beam of 35Cl+ cations is attracted to the negative plate while the beam of 35Cl– anions is attracted towards the positive plate. (b) Beryllium chloride is a simple molecule with an electron–deficient central atom. (i) Draw a ‘dot–and–cross’ diagram for the BeCl2 molecule. [1] Bex xCl Cl (ii) Name the shape of