NJC 2025 H1 Chemistry Prelim P2 QP

1 NJC/H1 Chem Preliminary Examination/02/2025 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 16 September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name, registration number and subject class on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer one question. At the end of the examination, fasten all your work securely together. A1 /13 A2 /13 Paper 2 /80 A3 /6 Paper 1 /30 A4 /11 Weightage A5 /10 Paper 1 (33%) /33 A6 /7 Paper 2 (67%) /67 B6 / B7 /20 Overall The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 21 printed pages and 1 blank page.

2 NJC/H1 Chem Preliminary Examination/02/2025 Section A Answer all the questions in this section in the spaces provided. 1 Boron, carbon, and lithium play critical roles in nuclear, organic, and battery chemistry. Their atomic structure and periodic behaviour provide important insights into chemical properties and bonding patterns. (a) (i) About 0.005% of water molecules consist of an oxygen atom bonded to two atoms of the isotope of hydrogen, deuterium, . The compound formed is deuterium oxide, D2O, and is also known as ‘heavy water’. Define the term isotope. ………………………………………………………………………………………… ………………………………………………………………………………………… [1] (ii) State the number of subatomic particles present in one molecule of D2O. number of protons number of neutrons number of electrons [1] (b) Separate beams of 14C2– and 7Li+ ions are passed through an electric field in the set- up below. The angle of deflection of the 14C2– beam is 7.0 o. Sketch on the diagram below, the paths taken by beams of 7Li+ and 14C2– ions in the presence of an electric field. Label your sketch clearly. [2]

3 NJC/H1 Chem Preliminary Examination/02/2025 [Turn over (c) The element sulfur has four naturally occurring isotopes as shown in Table 1.2. Table 1.2 isotope relative abundance / % 32S 94.93 33S 0.76 34S 4.29 36S 0.02 Use the relative abundance data to calculate the relative atomic mass of sulfur to 4 significant figures. Show your working. [2] (d) Write the electronic configuration of Cu and explain its anomaly ………………………………………………………………………………………….......... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………….. [2] (e) Predict and explain the order of first IE of Al, Mg, and S. ………………………………………………………………………………………….......... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………….. [2]

4 NJC/H1 Chem Preliminary Examination/02/2025 (f) (i) Draw the dot-and-cross diagram for PCl5. [1] (ii) Explain why PCl₅ exists but NCl₅ does not, in terms of electronic structure. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………… [2] [Total : 13]

5 NJC/H1 Chem Preliminary Examination/02/2025 [Turn over 2 Oxalic acid, found in many leafy vegetables, can be analysed via redox titration using potassium manganate(VII). This question explores thermochemistry and redox stoichiometry in food and materials chemistry. (a) To determine the standard enthalpy change of neutralisation, 60 cm 3 of 0.370 mol dm –3 aqueous ammonia was placed in a polystyrene cup. Constant volume of dilute HCl was added. The mixture was stirred after each addition and the maximum temperature was recorded. The following graph was obtained in Figure 2.1 Fig 2.1 (i) Define the term standard enthalpy change of neutralisation. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [1] (ii) Determine the maximum temperature change from Figure 2.1. [1]

6 NJC/H1 Chem Preliminary Examination/02/2025 (iii) Calculate the concentration of HCl used in the experiment. [2] (iv) Calculate the enthalpy change of neutralisation, ΔHno, for the reaction between HCl and ammonia. Assuming that the density of all aqueous solution is constant at 1.00 g cm –3 and specific heat capacity of the solution is 4.18 J g⁻¹ °C⁻¹. [2] (v) The theoretical standard enthalpy change of neutralisation is −57.0 kJ mol −1. Account for the discrepancy in the value calculated in (a)(iv). ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [1]

7 NJC/H1 Chem Preliminary Examination/02/2025 [Turn over (b) The following investigation was carried out on a sample of oxalic acid, H 2C2O4, extracted from 100 g of spinach (about one serving) using 50.0 cm 3 of an inert organic solvent. The solution is then titrated with acidified potassium manganate(VII), KMnO4. 2MnO4– + 16H+ + 5C2O42– → 10CO2 + 2Mn2+ + 8H2O Solutions used in the experiment: FA 1 The given inert organic solvent containing the oxalic acid was diluted with deionised water to a total volume of 250 cm3 in a volumetric flask. FA 2 1.0 mol dm–3 sulfuric acid, H2SO4 FA 3 0.0231 mol dm–3 potassium manganate(VII), KMnO4. Procedures: 1) 25.0 cm3 of FA 1 was first pipetted into a conical flask. 2) 25.0 cm3 of FA 2 and 40.0 cm3 of deionised water were then added to the same flask. 3) The resultant mixture was heated to a temperature of 65 oC over a Bunsen burner before being titrated with FA 3 from the burette. 4) 18.80 cm3 of FA 3 was required to react completely with the hot mixture. (i) The reaction between oxalate ion, C2O42– and MnO4− ion can be described by two half–equations. Write the two half-equations for this reaction. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [1] (ii) Determine the concentration, in mol dm–3, of C2O42– in FA 1. [2]

8 NJC/H1 Chem Preliminary Examination/02/2025 (iii) Calculate the mass of oxalic acid in one serving of spinach. [1] (iv) Assuming that spinach is the only dietary source of oxalic acid on a particular day, calculate the minimum number of servings of spinach must a healthy person, with a body weight of 65 kg, consume in a meal before he suffers from oxalic acid toxicity. You may assume toxicity limit is approx. 600 mg per kg body weight. [2] [Total: 13]

9 NJC/H1 Chem Preliminary Examination/02/2025 [Turn over 3 Nitrogen-containing compounds and small polyatomic species such as nitrogen trichloride (NC l₃) and hypochlorous acid (HOC l) exhibit a wide range of bonding arrangements, shapes, and physical properties. Understanding their electron configurations, molecular geometries, and intermolecular interactions is essential to predicting their chemical behaviour and phy