Yishun Town 2025 Prelim Chemistry Paper 2 (with Answer)

NAME: ( ) CLASS: YISHUN TOWN SECONDARY SCHOOL PRELIMINARY EXAMINATION 2025 SECONDARY 4 G3 CHEMISTRY (6092/2) DATE : 21 August 2025 DAY : Thursday DURATION : 1 h 45 min MARKS : 80 marks READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces provided at the top of this page. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer one question. Write your answers in the spaces provided. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You may use an approved calculator. A copy of the Periodic Table is printed on the last page. Section A Section B TOTAL This question paper consists of 18 printed pages, including the cover page.

2 SECTION A Answer all questions. 1 Some nuclide notations are given below. 1H 12C 14C 18O 56Fe 58Ni 65Zn Use the nuclide notations to answer the following questions. You may use them once, more than once or not at all. (a) Which is used as the basis for the definition of relative atomic and molecular masses? ……………………………………………………………………………………………………... [1] (b) Which is used in Haber Process? ……………………………………………………………………………………………………... [1] (c) Which is a metal but not a transition element? ……………………………………………………………………………………………………... [1] (d) Which two have the same number of neutrons? ……………………………………………………………………………………………………... [1] (e) Which two forms elements which are diatomic molecules? ……………………………………………………………………………………………………... [1] (f) Which two have the same chemical properties but different physical properties? ……………………………………………………………………………………………………... [1] [Total: 6]

3 2 Group 1 metals react with water. Group 1 metal reaction with water melting point / oC lithium sodium bubbles form rapidly with no flame potassium bubbles form very rapidly with flame rubidium explodes (a) (i) Complete the table above for the reaction of lithium with water. [1] (ii) The melting points of the four Group 1 metals shown above are 64 oC, 39 oC, 181 oC and 98 oC (not arranged in any sequence). Complete the table above with the correct melting points of the Group 1 metals. [1] (b) Two small 0.6 g pieces of lithium are reacted with 100 cm3 of water (an excess) at T1 oC and T2 oC respectively. The following graphs show the volume of gas produced when plotted against the time taken for the reactions. volume of gas / cm3 T1 oC T2 oC time / s (i) Use the graphs to explain whether T1 oC or T2 oC is at a higher temperature. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………... [2] (ii) Sketch a graph to show what would happen when 0.3 g of lithium is reacted with 100 cm3 of water at T1 oC. [1] [Total: 5]

4 3 The composition of polluted water is as shown. ion concentration of ion in polluted water / mg/dm3 ammonium 0.6 bromide 0.3 calcium 2.5 chloride 2.5 bicarbonate (HCO3–) 12.0 magnesium 0.8 nitrate 0.4 phosphate (PO43–) 0.5 potassium 5.3 silicate (SiO32–) 3.0 sodium 9.2 sulfate 0.5 (a) Write the formula of the compound formed from the Group 2 cation with the lower concentration and the anion with the highest concentration. ……………………………………………………………………………………………………... [1] (b) Calcium phosphate is insoluble in water. Calculate the maximum mass of calcium phosphate that can be precipitated from 100 cm3 of polluted water. (1 mg = 0.001 g) 3Ca2+ (aq) + 2PO43– (aq) ® Ca3(PO4)2 (s) [4] (c) (i) Suggest how you may test for the presence of chloride in the sample of polluted water. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………... [2]

5 (ii) Suggest why the sample may not give the intended result when tested for the presence of chloride. ……………………………………………………………………………………………………. ………………………………………………………………………………………………... [1] (d) Identify two compounds that can be used to prepare calcium chloride. You need to specify the state (solid or aqueous) of the substances clearly. ……………………………………………………………………………………………………... [2] (e) Polluted water may be cleaned using a suitable concentration of ethanoic acid. Ethanoic acid may stimulate the growth of naturally occurring bacteria which helps to break down certain pollutants. Some information about ethanoic acid and a model showing the dissociation of aqueous ethanoic acid are shown below. substance ethanoic acid, CH3CO2H solubility soluble in both water and organic solvents like alcohols nature weak acid which dissociates less than 1% in water density 1.05 g/cm3 melting point 16 oC boiling point 118 oC One inaccuracy depicted in the model is the fact that water molecules are not shown despite the solution being aqueous. Explain two other inaccuracies depicted by the model. Include relevant data or information in your explanation. ...………………………………………………………………………………………………………. …...……………………………………………………………………………………………………. ...………………………………………………………………………………………………………. ……………………………………………………………………………………………………... [2] [Total: 12] CH3CO2H CH3CO2H CH3CO2H CH3CO2H CH3CO2H CH3CO2– CH3CO2H CH3CO2H CH3CO2H H+ aqueous ethanoic acid

6 4 Sulfur has the ability to accommodate 12 electrons in its valence shell when it forms compounds. Two of these sulfur-containing compounds are sulfuryl fluoride (SO2F2) and sodium pyrosulfate (Na2S2O7). (a) The structural formula of sulfuryl fluoride is shown. Draw the dot-and-cross diagram for sulfuryl fluoride, showing only the valence electrons. F | O = S = O | F [2] (b) Sulfuryl fluoride can be prepared using two methods. The first method consists of a three-step reaction. Step 1: SO2 + KF ® KSO2F Step 2: KSO2F + Cl2 ® SO2ClF + KCl Step 3: SO2ClF + KSO2F ® SO2F2 + KCl + SO2 The second method produces sulfuryl fluoride by reacting sulfur dioxide with fluorine. SO2 + F2 ® SO2F2 (i) Write an overall equation for the first method to prepare sulfuryl fluoride. ………………………………………………………………………………………………... [1] (ii) Suggest the role of sulfur dioxide in the first method. ………………………………………………………………………………………………... [1] (iii) Explain the effect that sulfur dioxide can have on the environment. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………... [2]

7 (c) (i) Using the bond energy values given below, calculate the enthalpy change for the reaction of the second method. Note: The structure of SO2 is O = S = O. bond F – F S – F bond energy / kJ/mol 155 265 [2] (ii) Hence, draw an energy level diagram for the reaction of the second method. [3] (d) Sodium pyrosulfate is a colourless salt which reacts readily with water. When sodium pyrosulfate is heated to about 460 oC, it decomposes. Na2S2O7 ® Na2SO4 + SO3 In terms of oxidation numbers, explain whether the decomposition of sodium pyrosulfate is a redox reaction. …...……………………………………………………………………………………………………. ...………………………………………………………………………………………………………. ……………………………………………………………………………………………………... [2] [Total: 13]

8 5 This question is about the chemistry of chromium. Chromium is extracted from iron (II) chromite, FeCr2O4. Iron (II) chromite is first heated with sodium carbonate in the presence of oxygen to obtain sodium chromite. Reaction 1: 4FeCr2O4 + 8Na2CO3 +7O2 ® 8Na2CrO4 + 2Fe2O3 + 8CO2 Chromium is then extracted by treatin