2025 DHS H2 Chem Prelim Paper 2_Suggested Solutions

© DHS 2025 9729/02 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 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. 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 1 15 2 17 3 12 4 10 5 21 Total 75 This document consists of 16 printed pages.

2 © DHS 2025 9729/02 Answer all the questions in the spaces provided. 1 (a) Fig. 1.1 shows the relative first ionisation energies of six consecutive elements, A to F, in the Periodic Table with atomic number less than 20. The letters are not the symbols of the elements. Fig. 1.1 (i) Write an equation to represent the first ionisation energy of A. [1] A(g) → A+(g) + e− (ii) Explain why the first ionisation energy of F is more than that of E. [1] Both elements have similar shielding effect. However, F has a greater nuclear charge. Hence, F has a greater effective nuclear charge than E. The attraction between the nucleus and the outermost electron is stronger in F. (iii) Which element has the highest 4th ionisation energy? Explain your answer. [1] Element D. It is in Group 13 with outermost shell electronic configuration of ns2 np1. The 4th ionisation energy involves removal of an electron from an inner electron shell. Or 4th valence electron is removed from an inner electron shell. (iv) Element E is in Period 3. Identify element E and state the number of electron pairs in an atom of E. [1] element E is silicon number of electron pairs in an atom of E is 6 (b) 10.0 cm 3 of 0.10 mol dm −3 aqueous bromine was added to 50.00 cm 3 of a 0.10 mol dm−3 sodium hydroxide solution. The products formed were Br− and BrOx−. The excess sodium hydroxide required 15.00 cm3 of 0.20 mol dm−3 hydrochloric acid for complete neutralisation. Calculate the mole ratio between aqueous bromine and sodium hydroxide in the redox reaction.

3 © DHS 2025 9729/02 [Turn over Hence write a balanced equation for the reaction and deduce the value of x. [3] Initial amount of NaOH = 50.00 1000  0.10 = 5.00  10−3 mol amount of NaOH reacted with HCl(aq) = 15.00 1000  0.20 = 3.00  10−3 mol amount of NaOH reacted