TKGS 2026 Chem Prelim P2 MS

1 TANJONG KATONG GIRLS’ SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR EXPRESS CHEMISTRY CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 6092/02 Paper 2 14 August 2026 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, class and register number on all the work you hand in. Write in dark blue or black pen. You may use a HB 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. Overall -1m for all wrong units 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 23. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A Section B Total / 80 This document consists of 22 printed pages and 2 blank pages.

Tanjong Katong Girls’ School 2 Sec 4 Preliminary Examination 2026 Section A Answer all questions. 1 Table 1.1 shows information about the preparation of three pure samples of solid salts. Complete the table by filling in the missing information. Include state symbols with the formulae of the reagents. Table 1.1 formulae of salt formulae of reagent 1 formulae of reagent 2 method of preparation BaCO3 (s) Ba(OH)2 (aq) / Ba(NO3)2(aq) / BaCl2 (aq) K2CO3 (aq) / Na2CO3 (aq) / (NH4)2CO3 (aq)/ H2CO3 Any other group 1 carbonate precipitation filtration FeSO4 (s) FeO (s) / Fe(OH)2 (s) / FeCO3 (s) / Fe (s) H2SO4 (aq) addition of excess solid to acid evaporation and crystallisation NH4NO3 (s) NH3(aq)/ (NH4)2CO3/ NH4OH(aq) BOD HNO3 (aq) titration evaporation and crystallisation Key issues – chemical formula Penalise state symbols once for wrong or missing state symbols[Total: 5] 2 Hydrogen reacts with magnesium to form magnesium hydride, MgH2. Hydrogen reacts with oxygen to form water. (a) (i) Magnesium hydride is an ionic compound. Draw the dot -and-cross diagram of magnesium hydride, showing all the electrons. 1 for one Mg2+ showing all electrons

Tanjong Katong Girls’ School 3 Sec 4 Preliminary Examination 2026 1 for two H– ions (with both dot and cross drawn) (dot and cross are interchangeable) Issue – some students thought MgH2 is covalent [2] (ii) Water can partially dissociate to produce hydrogen ions and hydroxide ions. The structure of the hydroxide ion can be represented as shown. [O – H] – The electronic structure of hydrogen ion has been drawn below. Draw the dot -and-cross diagram of the hydroxide ion, showing the oute r shell electrons only. [2] 1 foreign electron on O drawn using another symbol) 1 for shared pair of e between O and H atom (dot and cross are interchangeable) Issue – some students drew 7 electrons for O (wrong symbol used) Hydrogen ion hydroxide ion (iii) Hence, in terms of electrons, explain why hydrogen exhibits the behaviour of both metals as well as non-metals. Hydrogen loses electron(s) which behaves as a metal. [1] Hydrogen shares electrons or gains electron(s) which behaves as a non-metal. [1] Issue – some students were not specific about metal/non- metals losing/gaining electrons H +

Tanjong Katong Girls’ School 4 Sec 4 Preliminary Examination 2026 (b) Explain, using structure and bonding, the difference in melting point between magnesium hydride and water. Magnesium hydride has a giant ionic (lattice) structure with strong electrostatic forces of attraction between (oppositely charged) ions. This requires a lot of energy to overcome/ weaken and hence high melting point [1m structure + bonding] Water has a simple covalent / simple molecular structure with weak intermolecular forces of attraction (between molecules). This requires low amount of energy to overcome/weaken and hence low melting point. [1m structure + bonding] [1m energy + mp, award independently] OR 1m for both structures/bonding 3 Table 3.1 below shows four different experiments that were conducted with various concentrations of three different acids that reacted with excess lumps of zinc. Table 3.1 experiment acid concentration of acid in mol / dm3 volume of acid in cm3 1 hydrochloric acid 0.10 100 2 hydrochloric acid 0.20 100 3 ethanoic acid 0.10 100 4 sulfuric acid M N (a) The chemical equation for the reaction between zinc and hydrochloric acid is shown. Zn + 2 HCl → ZnCl2 + H2 (i) Calculate the number of moles of hydrochloric acid that reacted in Experiment 1. No. of moles of acid = 0.10 x (𝟏𝟏𝟏𝟏𝟏𝟏 /𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏) = 0.0100 mol [1] moles of hydrochloric acid …………………… [1]

Tanjong Katong Girls’ School 5 Sec 4 Preliminary Examination 2026 (ii) Calculate the volume of gas that is evolved in Experiment 1. HCl : H 2 2 : 1 0.0100 : 0.005 [1] Volume of gas = 0.005 x 24 dm 3 = 0.120 dm3 or 120 cm3 [1] volume of gas ………………………… [2] (iii) Fig 3.1 shows the graph for Experiment 1. Sketch the graph for Experiment 2 in the same diagram below and label it as Expt 2. [1] Expt 2: faster speed and twice the yield [1] Expt 3: slower speed and same yield [1] Fig. 3.1

Tanjong Katong Girls’ School 6 Sec 4 Preliminary Examination 2026 (b) (i) Write a chemical equation for the reaction between ethanoic acid and zinc. 2CH3COOH + Zn → Zn(CH3COO)2 or (CH3COO)2Zn + H2 [1] (ii) Sketch the graph for Experiment 3 in the same diagram above and label it as Expt 3. [1] (iii) 0.10 mol/dm3 ethanoic acid has a higher pH than 0.10 mol/dm3 hydrochloric acid. Explain why. Ethanoic acid is a weak acid while hydrochloric acid is a strong acid. [1] Ethanoic acid dissociates partially in water to form lower concentration of H + ions. Hence it has a higher pH. [1] (c) Suggest a way to increase the rate of reaction in Experiment 1 , without changing the volume and concentration of the acid. Increase temperature or use powdered zinc [1] (d) Suggest values for M and N in the Table 3.1 such that Experiment 4 will have the same graph as Experiment 2. M: 0.10 mol/dm3 (2dp as per table) (✓) N: 100 cm3 (✓) 2(✓) : 1mark No units needed [Total: 10]

Tanjong Katong Girls’ School 7 Sec 4 Preliminary Examination 2026 4 Methane, methanol and hydrogen have been investigated as possible alternative sources of fuels for motor vehicles that currently use petrol. Table 4.1 below compares the energy released on combustion of these fuels. Table 4.1 fuel density in g / dm3 enthalpy change of combustion in kJ / mol enthalpy change of combustion in kJ / g