Copy of PLMGSS 2024 4E Chem P2 QP

1 CANDIDATE NAME CLASS CLASS INDEX NUMBER CENTRE NUMBER S INDEX NUMBER CHEMISTRY 6092/02 Paper 2 14 August 2024 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name and index number on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer one question. Write your answers in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 27. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A /70 Section B /10 Total /80 Paya Lebar Methodist Girls’ School (Secondary) Preliminary Examination 2024 Secondary 4 Express / G3 This document consists of 27 printed pages. [Turn Over

2 Section A Answer all questions. 1. Barium hydroxide, Ba(OH)2 is a strong base. Fig 1.1 shows a reaction scheme involving barium hydroxide. Fig. 1.1 (a) State what is observed in reaction 1. ……………………………………………………………………………………………… [1] (b) Suggest a reactant for reaction 2. ……………………………………………………………………………………………… [1] (c) Identify A. ……………………………………………………………………………………………… [1] (d) Ba(OH)2 is made by reaction of Ba with water. Write a balanced chemical equation for this reaction. ……………………………………………………………………………………………… [1]

3 (e) The mineral barytocalcite contains both BaCO3 and CaCO3. Both compounds decompose on heating. (i) Using your knowledge on the reactivity of metals, predict which compound decomposes first when barytocalcite is heated. Explain your answer. ………………………………………………………………………………………….. ………………………………………………………………………………………….. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………...… [2] (ii) Construct an equation for the complete thermal decomposition of barium carbonate. ……………………………………………………………………………………… [1] [Total: 7] 2. The elements phosphorus, sulfur and chlorine are elements in Period 3 of the Periodic Table. Table 2.1 shows some properties of these three elements. property P S Cl number of valence electrons 5 6 7 formula of most common ion P3- S2- Cl- Table 2.1 (a) P3-, S2- and Cl- have the same number of electrons. Describe and explain the trend in ionic radius shown by P3-, S2- and Cl-. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ……………………………………………………………………………………………… [2] [Turn Over

4 (b) Chlorine forms various ions with different oxidation states. Table 2.2 shows some of the ions of chlorine. Ion chlorate perchlorate hypochlorite chloride formula ClO3- ClO4- ClO- Cl- oxidation state of chlorine Table 2.2 (i) Fill in Table 2.2 with the oxidation state of the chlorine in the various ions. [2] (ii) A disproportionation reaction is a reaction where an element is both reduced and oxidised at the same time. Potassium chlorate, KClO3 decomposes according to equation below. 4KClO3 → 3KClO4 + KCl Explain why the above reaction is a disproportionation reaction. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ……………………………………………………………………………………… [2] (c) A student does two tests on separate samples of NaCl(aq). Complete Table 2.3 with the correct observations for each test. test observation addition of a few drops of Br2(aq) addition of a few drops of AgNO3(aq) [2] Table 2.3 [Total: 8]

5 3. POCl3 has a melting point of 1°C and a boiling point of 106°C. (a) Based on the information provided, suggest the structure and bonding in POCl3. ………………………………………………………………………………………………… ……………………………………………………………………………………………… [1] (b) Phosphorus shares a double bond with oxygen. Draw the ‘dot and cross’ diagram to show the bonding in POCl3. Show only the outermost electrons. [2] [Turn Over

6 (c) POCl3(g) forms when PCl3(g) reacts with O2(g). Table 3.1 shows some relevant information on energy changes. Table 3.1 Calculate the enthalpy change, ∆H, for the reaction shown in the equation in (c). enthalpy change = ………………. kJ [2] (d) Hence, draw the energy profile diagram in Fig. 3.1 for the reaction shown in (c). Indicate clearly the value of the activation energy and enthalpy change on Fig. 3.1. Fig. 3.1 [3] [Total: 8] Process value/ kJ mol-1 enthalpy change for breaking bonds in one mole of PCl3 +289 enthalpy change for forming bonds in one mole of POCl3 -592 O2 (g) → 2O (g) +496 progress of reaction energy

7 4. Concentrated aqueous magnesium iodide and molten magnesium iodide are electrolysed separately using graphite electrodes. (a) Describe one similarity and one difference in terms of the products formed at the electrodes for the different electrolytes. One similarity: ……………………………………………………………………………….. ……………………………………………………………………………………………… [1] One difference: …………………………………………………………………………….... ……………………………………………………………………………………………… [1] (b) Describe and explain what is observed when aqueous chlorine is bubbled into aqueous magnesium iodide. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ……………………………………………………………………………………………… [2] (c) Iodide ions react with manganese (IV) oxide as shown in the equation. Explain the role played by the iodide ions in the reaction, in terms of oxidation state. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2] [Turn Over

8 (d) Iodine has several radioactive isotopes. Two of the isotopes, iodine-131 and iodine-123 has clinical usage. Tiny amounts of radiation that are emitted by the radioactive iodine isotopes help the doctor to see how the organ is functioning or to treat certain cancers. Radiation emitted can be in the form of a beta particle, 𝛽−1 0 . (i) Explain whether iodine-131 and iodine-123 will have similar chemical properties. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………… [1] (ii) The equation below shows iodine-131 breaking down to produce a beta particle. 𝐼53 131 → 𝑋𝑒54 131 + 𝛽−1 0 Radioactive phosphorus-32 also breaks down to produce a beta particle, similar to radioactive iodine-131. Write an equation to show this reaction. …………………………………………………………………………………..……… [1] [Total: 8]

9 5. A piece of copper ore containing copper (II) oxide has a mass of 0.567g. It is dissolved in an acid, giving 100.0 cm3 of a blue solution in which all the copper is present as Cu2+ ions. An excess of KI (aq) is added to a 25.0 cm3 sample of this solution. All the copper is precipitated as white CuI(s). Cu2+ ions are the only component in the solution that react with KI (aq). This is reaction 1. The liberated iodine is then titrated with 0.0200 mol/dm3 of S2O32-. This is reaction 2. The titration requires 20.10 cm3 of 0.0200 mol/dm3 of S2O32- to reach the end point. (a) Calculate the number of moles of I2 that are reduced in the titration.