RVHS Prelim H2 Chemistry P2 QP

River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination [Turn over RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 2 4 J CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 16 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, class and name on all the work that you hand in. 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. DO NOT WRITE IN ANY BARCODES. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. The use of an approved scientific calculator is expected, where appropriate. 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 Question Number 1 2 3 4 5 6 Marks 13 15 9 16 10 12 significant figures units Total 75 This document consists of 28 printed pages.

2 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination 1 (a) Fig. 1.1 shows the successive ionisation energies of an element A in Period 3. Fig. 1.1 (i) Explain why the successive ionisation energies of element A increase as shown in the graph. ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... [1] (ii) Identify which group element A belongs to. Explain your reasoning. ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... [2]

3 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination [Turn over (b) Calcium and scandium are both found in Period 4 of the Periodic Table. Explain why the atomic radius of scandium is smaller than that of calcium. ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... [2] (c) Like Group 2 carbonates, the hydroxides of Group 2 elements can undergo thermal decomposition. In the process, water vapour is produced. (i) Write an equation for the decomposition of calcium hydroxide. ……………………..………………………………………………….......... ……………………..………………………………………………….......... [1] (ii) Nickel(II) hydroxide can undergo thermal decomposition similar to calcium hydroxide. Given that the atomic radius of scandium and nickel are approximately similar, deduce whether nickel( II) hydroxide would decompose at a higher or lower temperature than calcium hydroxide. Explain your reasoning. ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... ……………………..………………………………………………….......... [2]

4 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination (d) Nickel(II) compounds can be analysed using dimethylglyoxime (C4H8N2O2). dimethylglyoxime C4H8N2O2 An excess of a solution of dimethylglyoxime is first added to an acidic solution of a nickel(II) compound. When aqueous ammonia is next added, a nickel(II) complex, Ni(C4H7N2O2)2, is produced. The following equation shows the reaction: [Ni(H2O)6]2+ + 2C4H8N2O2 + 2NH3 ⎯→ Ni(C4H7N2O2)2 + 2NH4+ + 6H2O (i) State the role of ammonia in the above reaction. ……………………..………………………………………………….......... ……………………..………………………………………………….......... [1] (ii) Draw the structure of C4H7N2O2−. [1] (iii) The Ni(C4H7N2O2)2 complex is square planar in shape with respect to the nickel( II) ion. Each ligand in the complex is bidentate with the nitrogen atoms datively bonded to the nickel( II) ion. The –OH group in each ligand forms a hydrogen bond with another ligand. Complete Fig. 1.2 to show the structure of the Ni(C4H7N2O2)2 complex and label one of the two hydrogen bonds clearly. Ni2+ Fig. 1.2 [2]

5 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination [Turn over (iv) In the formation of a square planar complex, the ligands approach the central metal ion along the x and y axes. Fig. 1.3 shows how the 3d orbitals of the nickel( II) ion in a square planar complex are split based on the crystal field theory. Fig. 1.3 State the identity of the 3d orbital with the highest energy in the nickel(II) ion in a square planar complex. ……………………..………………………………………………….......... [1] [Total: 13]

6 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination 2 Nicotine is a weak diprotic base consisting of an aromatic pyridine ring joined to a saturated pyrrolidine ring. It is highly addictive and is found in tobacco and vapes. Values for the base dissociation constants, pKb, for nicotine is shown below. (a) State what is meant by the term Lewis base. ……………………………………………………………………………………... ……………………………………………………………………………………... [1] (b) 25.00 cm3 of an aqueous solution of nicotine was titrated against 0.100 mol dm−3 hydrochloric acid, HCl. At the 2nd equivalence point, it was found that 49.0 cm3 of HCl was added. (i) Calculate the concentration of NicotineH22+, in mol dm –3, at the 2nd equivalence point. [1] (ii) Calculate the pH of the solution at the 2nd equivalence point. [2]

7 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination [Turn over (iii) Prove that the initial pH of nicotine is 10.5. [3] (iv) Sketch the shape of the pH curve of nicotine against the volume of HCl added on Fig. 2.1 using all relevant information given or calculated. Mark clearly where the equivalence points occur. Fig. 2.1 [1] 14 7 0 0 49.0 Volume of HCl added/ cm 3 pH

8 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination (c) Aqueous solutions of X, Y and Z are basic. Fig. 2.2 shows them listed in decreasing order of basicity. most basic least basic X Y Z Fig. 2.2 Explain the relative basicities of aqueous solutions of X, Y and Z in terms of their structures. ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... [3]

9 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination [Turn over (d) The f ollowing diagram shows the partial synthesis route of nicotine formation: (i) Suggest the type of reaction in Step 1. ………………………………………………………………………………. [1]

10 River Valley High School 9729/02/PRELIMS/25 2025 Preliminary Examination (ii) Complete Fig. 2.3 to suggest a mechanism for this reaction. Show the structure of the intermediate and the movement of the lone pairs, dipoles, curly arrows and charges. Fig. 2.3 [2] (iii) Suggest the reagent and conditions for Step 2. ………………………………………………………………………………. [1] [Total: 15]