2024 Prelims TJC H2 Chem P2 (QP)

9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/02 Paper 2 Structured Questions 21 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and class on all the work 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. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in bracket [ ] at the end of each question or part question. This document consists of 21 printed pages and 3 blank pages. For Examiner’s Use Paper 1 /30 Paper 2 Q1 / 14 Q2 / 15 Q3 / 16 Q4 / 20 Q5 / 10 Total /75 Paper 3 /80 TOTAL (%) /100

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Answer all questions in the spaces provided. 1 (a) Table 1.1 shows the successive ionisation energies of an element A. Table 1.1 ionisation energies / kJ mol−1 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th element A 945 1794 2735 4839 6056 11690 14180 17370 20550 23830 (i) Explain why the successive ionisation energies of an element always increase. [1] (ii) Element A is in Period 4. Using information from Table 1.1 and the Data Booklet, identify element A. Explain your answer clearly. [2] (iii) State and explain how the first ionisation energy of element A will compare to that of the element to its right in the Periodic Table. [2]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (b) (i) With the aid of a labelled diagram. describe the structure and bonding of barium. [2] (ii) Explain the trend in atomic radii down Group 2. [2] (iii) The density of magnesium and barium is 1.7 g cm–3 and 3.6 g cm–3 respectively. Explain why the density of barium is significantly greater than that of magnesium. [1]

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (iv) When magnesium is burned in air, a mixture of the ionic solids magnesium oxide and magnesium nitride, Mg3N2, is formed. Adding water to Mg3N2 produces an alkaline gas and a white insoluble solid. Suggest an equation for the reaction between Mg3N2 and water, and use it to calculate the mass of white insoluble solid that would be formed from 2.0g of Mg3N2. [2] (c) The scientific community was shocked at the recent claim of the discovery of an isotope of a new element, unbibium, with a mass number of 292. This is over 50 mass units higher than uranium, the heaviest known naturally -occurring element. There is a possibility that there is an ‘island of stability’ beyond the known Periodic Table at some very high atomic numbers. (i) The scientists suggested that the atomic number of unbibium is 122. How many neutrons are there in this isotope? [1] (ii) If unbibium really exists then it will require a new block of the Periodic Table, corresponding to the occupancy of another type of subshell, beyond the s, p, d and f. This would be a g subshell, which is predicted to be found in the 5 th shell of an atom, i.e. the 5g subshell. Based on the sequence of subshells in the Periodic Table, s, p, d, f, predict how many orbitals there are in a g subshell. [1] [Total: 14]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over 2 (a) The halogens and their compounds have many applications. (i) Explain, in terms of structure and bonding, the trend in the volatility of the halogens. [2] (ii) When heated in chlorine, phosphorous form phosphorus pentachloride, PCl5. Explain the reaction of PCl5 with water. Include the pH value of the resulting solution and write equation for the reaction that occurs. [2] There is said to be a diagonal relationship between elements of the second and third periods of the Periodic Table. (iii) By analogy with the reaction of SiCl4, suggest a balanced equation for the hydrolysis of BCl3. [1] (iv) Explain why BCl3 can undergo hydrolysis like SiCl4. [1]

6 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (b) Oxoanions of Group 17 elements have the general formula XO m–, where m = 1, 2, 3 or 4. These oxoanions are strong oxidising agents. (i) Suggest why fluorine does not form higher oxoanions where m  2. [1] (ii) Draw the structure of the ClO3– ion to show its shape. [1] 1.25 x 10-3 mol of an aqueous bromate salt containing the BrOm– anion was added to excess potassium iodide. The resulting mixture was washed with hexane to dissolve the iodine, and the aqueous and organic layers were separated. Upon adding silver nitrate to the aqueous layer, a yellow precipitate and a pale cream precipitate were obtained. (iii) Identify the two precipitates formed. [1] (iv) The iodine collected in the organic layer was titrated against 0.500 mol dm -3 sodium thiosulfate. 14.90 cm3 of titrant was required to discharge the blue-black colour of the starch indicator. Calculate the number of moles of electrons transferred per mole of BrOm–. Hence determine the value of m. [2]

7 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (c) Fig. 2.1 shows two cells connected in series. Cell 1 and Cell 2 involve the electrolysis of saturated solution of CuBr 2 and concentrated HX respectively, where X is one of the Group 17 elements. Fig. 2.1 (i) Write ion-electron equations for the reactions occurring at the cathode and anode in Cell 1 during electrolysis. [2] (ii) A current of 22.8 A was passed through the saturated solution of CuBr2 in Cell 1. After 10 minutes, a halogen is formed at one of the electrodes in Cell 2 and is collected by a syringe. It is found that the mass of the syringe increased by 5.04 g. Identify X by calculating the Mr of the halogen produced. [2] [Total: 15] Concentrated HX Pt Saturated CuBr2(aq) Pt Cell 1 Cell 2 + -

8 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 3 Table 3.1 shows the enthalpy change of combustion and hydrogenation of some substances. Table 3.1 Substances ∆Hcombustion /