TKGS 2026 Chem Prelim P2 QP

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. 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) ………………….. ………………… precipitation filtration FeSO4 (s) …………………... H2SO4 (aq) addition of excess solid to acid evaporation and crystallisation NH4NO3 (s) …………………... HNO3 (aq) ……………………………. evaporation and crystallisation [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. [2]

Tanjong Katong Girls’ School 3 Sec 4 Preliminary Examination 2026 (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] hydrogen ion hydroxide ion (iii) Hence, in terms of electrons, explain why hydrogen exhibits the behaviour of both metals as well as non-metals. ………………………………………………..…………………………………… …………………………………………………..………………………………… …………………………………………………………………………………. [2] (b) Explain, using structure and bonding, the difference in melting point between magnesium hydride and water. …...……………………………………………………………………………………….. …….…...…………………………………………………………………………………. …………………………………………………………………………………………….. …………………………………………………………………………………………. [3] [Total:9] H +

Tanjong Katong Girls’ School 4 Sec 4 Preliminary Examination 2026 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. moles of hydrochloric acid …………………… [1] (ii) Calculate the volume of gas that is evolved in Experiment 1. volume of gas ………………………… [2]

Tanjong Katong Girls’ School 5 Sec 4 Preliminary Examination 2026 (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] Fig. 3.1 (b) (i) Write a chemical equation for the reaction between ethanoic acid and zinc. ………………………………………………………………………………….. [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. ……………………………………………………………………………………... ……………………………………………………………………………………... ………………………………………………………………………………….. [2] Time / s Volume of gas / cm3

Tanjong Katong Girls’ School 6 Sec 4 Preliminary Examination 2026 (c) Suggest a way to increase the rate of reaction in Experiment 1 , without changing the volume and concentration of the acid. ……………………………………………………………………………………......... [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: ……………………….. N: ………………………….. [1] [Total: 10] 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 petrol 710 – 770 – – 47.3 methane 0.667 – 890 – 55.7 methanol 792 – 726 hydrogen 0.0884 – 285 – 142.5 (a) (i) Calculate the enthalpy change of combustion for methanol in kJ / g. [1] (ii) Suggest why no value is quoted for the enthalpy change of combustion for petrol in the table above. ……………………………………………………………………………………... ………………………………………………………………………………….. [1]

Tanjong Katong Girls’ School 7 Sec 4 Preliminary Examination 2026 (b) (i) The equation shows the combustion of methane. CH4 + 2 O2 → CO2 + 2 H2O Using ideas about bond breaking and bond forming, explain why the enthalpy change for the complete combustion of methane has a negative sign. ………………………………………………………………………………..……. …………………………………………………………………………………..…. …………………………………………………………………………………. [2] (ii) Draw an energy profile diagram for the complete combustion of methane. Indicate the enthalpy change, ∆H and activation energy, Ea on the diagram clearly. [3] (c) Other than the amount of heat given out , s tate one advantage and one disadvantage of using methanol as a fuel compared to hydrogen advantage: ………………..……..………………………………………………………. …………..…………………………………………………………………… disadvantage: ……….…………………………………………………………………… ..………………………………………………………………………….. ..………………………………………………………………………. [2]