ZHSS 2026 Chem Prelim P2 QP

ZHONGHUA SECONDARY SCHOOL PRELIMINARY EXAMINATION 2026 SECONDARY 4 EXPRESS Candidate Name Class Register Number CHEMISTRY 6092 /02 Paper 2 19 August 2026 1 hour 45 minutes Additional Materials: NIL READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces at the top of this page and on all separate answer paper used. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer one questions. 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 24. The use of an approved scientific calculator is expected, where appropriate. O For Examiner’s Use Actual Maximum Marks Section A 70 Section B 10 Total 80 This document consists of 24 printed pages.

2 Section A Answer all the questions. 1 Choose from the following equations to answer the questions below. A Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s) B H⁺(aq) + HCO₃⁻(aq) → CO₂(g) + H₂O(l) C Ag⁺(aq) + Cl⁻(aq) → AgCl(s) D Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq) E Fe³⁺(aq) + e⁻ → Fe²⁺(aq) F 2Br⁻(aq) → Br₂(aq) + 2e⁻ G MgCO₃(s) + 2H⁺(aq) → Mg²⁺(aq) + CO₂(g) + H₂O(l) H NH₄Cl (aq) + NaOH(aq) → NH₃(g) + NaCl (aq) + H₂O(l) Each equation can be used once, more than once or not at all. State the letter A to H for the equation which shows (a) the production of a gas that turns moist red litmus paper blue, [1] (b) the formation of a white precipitate, [1] (c) only an oxidation reaction, [1] (d) a reaction in which a more reactive metal displaces a less reactive metal from its salt solution, [1] (e) a halogen displacement reaction. [1] [Total:5]

3 [Turn over 2 Table 2.1 provides some information on two different forms of carbon allotropes and silicon. Table 2.1 substance melting point / °C electrical conductivity uses carbon allotrope A above 3000 poor cutting tools, drill bits carbon allotrope B above 3000 good lubricant silicon 1414 good semiconductors in electronics (a) Explain, in terms of structure and bonding, why carbon allotrope A is used as a drill bit while carbon allotrope B is used as a lubricant. [4] (b) The structure of silicon is shown in Fig. 2.1 Fig. 2.1 This structure alone is unable to account for one of its physical properties stated in Table 2.1. State this physical property and explain why the structure shown does not fully explain it. [2] Legend: represents a silicon atom

4 (c) Methane, is a simple covalent molecule containing carbon. (i) Draw a ‘dot-and-cross’ diagram to show the bonding in a methane molecule. Show outer electrons only. [2] (ii) Use your diagram in (c)(i) to explain how the carbon and hydrogen atoms in methane achieve a stable electronic configuration. [1] [Total:9]

5 [Turn over 3 A student conducted two experiments using calcium carbonate and sulfuric acid. CaCO3 + H2SO4 → CaSO4 + H2O + CO2 At every minute, the volume of carbon dioxide gas collected was measured and the results were plotted in a graph shown in Fig. 3.1. The details of the experiment are shown in Table 3.1. Table 3.1 experiment number of moles of calcium carbonate/ mol number of moles of sulfuric acid/ mol concentration of sulfuric acid/ mol/dm3 1 0.06 0.05 2.00 2 0.06 0.02 4.00 (a) Sketch the graph for experiment 2 in Fig. 3.1 and label it as experiment 2. [2] time/s volume of gas/ dm3 1.20 experiment 1 Fig. 3.1

6 (b) A third experiment was conducted by the student. 40 cm 3 of 2 mol/dm 3 of phosphoric acid, H3PO4 was added to 6 g of calcium carbonate. Phosphoric acid is a weak acid. (i) Construct a balanced chemical equation for the reaction between calcium carbonate and phosphoric acid. [1] (ii) Deduce the limiting reactant in this reaction. Show your working. limiting reactant [2] (c) Explain, in terms of Collision Theory, why a weak acid affects the rate of reaction. [3] [Total: 8]

7 [Turn over 4 A water treatment plant uses metal pipes to transport water. Experiments are carried out on various metals to determine their suitability for use. In experiment 1, hydrogen gas was passed separately over the heated oxides of the three metals in the combustion tube. The results are given in the Table 4.1. Table 4.1 metal oxide chemical formula appearance before heating appearance after heating cobalt oxide CoO green powder grey powder and a colourless liquid on the side of the glass tube gallium oxide Ga2O3 white powder white powder and no liquid on glass tube bismuth oxide Bi2O3 yellow powder grey powder and a colourless liquid on the side of the glass tube In experiment 2, pieces of bismuth, gallium and cobalt were added separately to a solution of lead(II) nitrate, Pb(NO3)2. The results are given in Table 4.2. Table 4.2 cobalt gallium bismuth Grey solid formed on cobalt. The solution slowly turned pink. Grey solid formed on gallium. The solution remained colourless. No change in bismuth metal or in solution. (a) Using the observations from Table 4.1, identify the two metal oxides that were reduced by hydrogen. Explain your answer. [2] (b) Using the observations from Table 4.1 and Table 4.2, arrange the four metals bismuth, cobalt, gallium, and lead in order of decreasing reactivity. [1] (c) Write the ionic equation, including state symbols, for the reaction between cobalt and lead(II) nitrate solution. [2]

8 (d) The metals selected are used in equipment at a water treatment plant. After suspended impurities are removed, chlorine is added to disinfect the water before it is supplied to homes. Chlorine reacts with cold aqueous sodium hydroxide to produce sodium chlorate(I), the active ingredient in many household bleaches and disinfectants. Cl2 + 2OH− → Cl− + ClO− + H2O The chlorate(I) ion is unstable and decomposes when heated. 3ClO−→ 2Cl− + ClO3− (i) Determine the oxidation number of chlorine in Cl₂, Cl⁻, ClO⁻ and ClO₃⁻. species Cl2 Cl⁻ ClO- ClO₃⁻ oxidation number [2] (ii) Explain, in terms of oxidation numbers in (d)(i), why chlorine in chlorate(I) ions behaves as both an oxidising agent and a reducing agent. [2] [Total: 9]

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