2025 JYSS Pure Chem Prelim P2

JUNYUAN SECONDARY SCHOOL Secondary Four Express Preliminary Examination 2025 CANDIDATE NAME CLASS CHEMISTRY 6092 / 02 Paper 2 28 Aug 2025 1 hour 45 min Candidates answer on the Question Paper. No additional materials are required. READ THESE INSTRUCTIONS FIRST Write your name, index number and name on all the work you hand in. Write in dark blue or black pen. You may use an 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 in page 26. The use of an approved scientific calculator is expected, where appropriate. This document consists of 24 printed pages and 2 blank pages. For Examiner’s Use Section A Section B Total INDEX NUMBER 80

2 6092/02/O/4E/Prelim/25 Section A Answer all questions. 1 Use the compounds listed below to answer the following questions. Zn(NO3)2 MgO Al(NO3)3 CO Na2SO4 PbO NO2 You may use the compound once, more than once or not at all. State a: (a) soluble compound that reacts with excess aqueous ammonia to produce a white precipitate. ……………………………………………………………………………………………..………[1] (b) compound that causes acid rain when released into the atmosphere. ……………………………………………………………………………………………..………[1] (c) metal oxide that can be reduced by hydrogen gas. ……………………………………………………………………………………………..………[1] (d) compound that reacts with aqueous sodium hydroxide to form a salt and water. ………………………………………………………….…………………………………..…..…[1] (e) compound that can be prepared by titration. ………………………………………………………….…………………………………..…..…[1] [Total: 5]

3 6092/02/O/4E/Prelim/25 2 Chlorophyll is a green pigment found in green leaves. When these leaves are harvested and become less fresh, the chlorophyll can decompose into phaeophytin, which is a grey pigment. A student carries out a chromatographic experiment to compare the extracts of spinach leaves obtained from two different sources. Fig. 2.1 shows the chromatogram obtained. Fig. 2.1 (a) Calculate the Rf value of chlorophyll in the experiment. [1] (b) Using the results from Fig. 2.1, compare the freshness of frozen spinach to spinach bought from the market. Explain your reasoning. ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..………[2] (c) State two other conclusions that can be made about the extract from frozen spinach in terms of the solubility and number of components. ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..………[2] [Total: 5] solvent front

4 6092/02/O/4E/Prelim/25 3 In 1897, J.J. Thompson discovered electrons. In 1904, electrons were first incorporated into the model of an atom , called the ‘Plum Pudding’ model by Thompson. Fig. 3.1 shows the ‘Plum Pudding’ model of an atom. Fig. 3.1 (a) List three features of the ‘Plum Pudding’ model in Fig. 3.1 that are inaccurate in this current age. ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..………[3] (b) Based on the ‘Plum Pudding’ model and the understanding of subatomic particles, a student proposed a model of the ion formed by the atom in Fig. 3.1. Fig. 3.2 shows the proposed model. Fig. 3.2 In terms of the number of subatomic particles, explain why the model in Fig. 3.2 is also not an accurate representation of the structure of the ion formed. ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..………[2] diagrammatic example of an atom comprising of 11 electrons scattered throughout a spherical cloud of positive charge.

5 6092/02/O/4E/Prelim/25 (c) Further experiments led to more accurate development s of the atomic model , leading to the identification of three subatomic particles . In one of these experiments, a beam of subatomic particles x, y and z was passed through a pair of oppositely charged plates. Fig. 3.3 shows how the particles were affected. Fig. 3.3 From the results in Fig. 3.3, deduce the nature of the charge on each of the particles x, y and z. Support your deductions with evidence. ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..……….... ……………………………………………………………………………………………..………[3] [Total: 8]

6 6092/02/O/4E/Prelim/25 4 Phosphorus is an interesting element that can exist in several forms with very different properties. Fig. 4.1 shows the structures and melting points of two forms of phosphorus. Fig. 4.1 (a) Describe the similarities and differences in the bonding and structures of the two forms of phosphorus. …………………………………………………………………………………………….……….... …………………………………………………………………………………………….……….... ……………………………………………………………………………………………….…….... …………………………………………………………………………………..………..………[3] (b) Fig. 4.2 shows the structures of some substances containing phosphorus. Fig. 4.2

7 6092/02/O/4E/Prelim/25 (i) Draw a ‘dot-and-cross’ diagram to show the bonding in a phosphonium ion. Show the outer shell electrons only. [2] (ii) The following are statements about the substances containing phosphorus. Using Fig. 4.2 and your understanding of bonding and structure , put a tick ( ✓) in one box in each row, to show which statements are true and which are false. true false Sodium phosphide is likely to be insoluble in water. Phosphorus trioxide is likely to be a poor conductor of electricity. Phosphine is likely to be a gas at room temperature. [2] [Total: 7]

8 6092/02/O/4E/Prelim/25 5 A class of students received a home-based learning assignment involving the use of ‘invisible ink’ to conceal a written message. The idea behind the design of invisible inks requires a colourless substance that produces a coloured product when a “revealer” is applied. Fig. 5.1 (a) Phenolphthalein is an acid-base indicator. It is colourless in solutions with pH less than 10 and pink in solutions with pH above 10 . Phenolphthalein is a suitable reagent for making an invisible ink. (i) Suggest the name of a suitable ‘revealer’ for the invisible ink made of phenolphthalein. ……………..…………………………………………….......…………………………….[1] (ii) The revealed message was left in the open to dry. After a few days, it was observed that the ink started to fade. A student suggests that the drying led to a lower concentration of hydroxide ions which then affected the pH. Explain why the student is likely to be correct and how the pH is affected. …………..……..……………………………………….......……………………………....... …………..……..……………………………………….......……………………………....... ……………..…………………………………………….......…………………………….[2] a message written in invisible ink, previously unseen applying a cotton bud soaked in the aqueous ‘revealer’ causes the message to appear

9 6092/02/O/4E/Prelim/25 (b) The students are tasked to design new pairs of invisible ink