PRSS 4E Chemistry Prelim 2023 P2

Name Class Register No. SECONDARY 4 EXPRESS PRELIMINARY EXAMINATION 2023 CHEMISTRY Paper 2 Friday 1035 – 1220 6092/02 18 Aug 2023 1 h 45 min 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 soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions in the spaces provided. Section B Answer all three questions, the last question is in the form either/or. Answer all questions in the spaces provided. At the end of the examination, fasten all your work securely together. 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 22. The use of an approved scientific calculator is expected, where appropriate. This document consists of 22 printed pages, including the cover page. Setter: Ms Chua Wei Tian [Turn over Pasir Ris Secondary School For Examiner’s Use Section A B9 B10 B11 Total

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 2 Section A Answer all the questions in the spaces provided. The total mark for this section is 50. A1 Fig. 1.1 shows the electronic configurations of five elements, A, B, C, D and E. Fig. 1.1 (a) Use the letters A, B, C, D and E to answer the following questions. Each letter may be used once, more than once or not at all. (i) Which element is most likely to be a metal with low melting point? ……………………………………………………………………………………………………….. [1] (ii) Which element can be oxidised by oxygen to form an amphoteric oxide? ……………………………………………………………………………………………………….. [1] (iii) Which element can form a molecule with a double covalent bond? ……………………………………………………………………………………………………….. [1] (b) Element E exists as a single atom only. Explain why. …………………………………………………………………………………………………………………... …………………………………………………………………………………………………….………… [1] [Total: 4]

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 3 A2 Table 2.1 shows the formulae of oxides of elements across Period 2 and Period 3 in the Periodic Table. Table 2.1 Period Group I II III IV V VI VII 2 Li2O BeO B2O3 CO2 NO2 - F2O 3 Na2O MgO Al2O3 SiO2 P2O5 SO2 Cl2O (a) Carbon and sili con are elements in Group IV of the Periodic Table. They form oxides with very different melting points. Explain, in terms of structure and bondi ng, why the melting points of carbon dioxide and silic on dioxide are different. …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………... …………………………………………………………………………………………………….………… [3] (b) (i) Draw a ‘dot-and-cross’ diagram to show the bonding in Na 2O. Show only the valence electrons. [2]

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 4 (ii) Discuss the differences in the type of bonding and the way bonds formed in Na2O and Cl2O. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………….……….. [2] [Total: 7] A3 Mixture S contains one cation and two anions. A series of tests was performed on mixture S as shown in Fig. 3.1. Fig. 3.1 (a) Identify the following unknown substances: (i) T, …………………………………………………………………………………………………….. [1] (ii) U, …………………………………………………………………………………………………….. [1] (iii) V, …………………………………………………………………………………………………….. [1] (iv) W. ………………………………………………………………………………………………….. [1]

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 5 (b) Suggest the likely identities of the ions present in mixture S. …………………………………………………………………………………………………………...….. [1] (c) Write a balanced chemical equation to represent one of the reactions in Fig. 3.1. …………………………………………………………………………………………………………...….. [1] [Total: 6] A4 All Group I metals form metal hydroxides that are soluble i n water. Most other metal hydroxides are insoluble in water. Crystals of lithium chloride can be prepared using titration between aqueous hydrochloric acid and aqueous lithium hydroxide. Fig. 4.1. represents the experimental set-up. Fig. 4.1 25.0 cm3 of aqueous lithium hydroxide is pipetted into the conical flask. A few drops of an indicator are added. Aqueous hydrochloric acid is added until the indicator just changes colour. The volume of acid required to completely neutralise lithium hydroxide is recorded.

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 6 (a) A neutral solution of lithium chloride containing the indicator is left at the end of titration. It is known that lithium chloride is unstable to heat and melts at 617°C. Describe how you could obtain a pure dry sample of lithium chloride crystals. …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………...….. [2] (b) Suggest why magnesium chloride could not be prepared using the same method as lithium chloride. …………………………………………………………………………………………………………………... …………………………………………………………………………………………………………...….. [1] (c) The concentration of aqueous hydrochloric ac id is 2.70 mol/dm 3. 22.50 cm 3 of aqueous hydrochloric acid is required to neutralise 25.0 cm3 of aqueous lithium hydroxide. Calculate the concentration of aqueous lithium hydroxide. [2] [Total: 5]

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 7 A5 Table 5.1 shows the melting points and boiling points of Group VII elements. Table 5.1 Group element melting point / °C boiling point / °C VII chlorine –101 –35 bromine –7 59 iodine 114 184 (a) Describe the trend of melting point s and boiling points of elements down Group VII. Use ideas about bonding to explain why. ………………………………………………………………………………………….……………….……. ………………………………………………………………………………………….…………………. …………………………………………………………………………………………….………………. …………………………………………………………………………………….…...........……………. [2] (b) Sea water cont ains potassium bromide. Bromine can be produced from sea water by displacement. (i) Name an element that can displace bromine. Explain your answer. …………………………………………….…………………………………………….………………. ………………………………………………………………………….……………...……………. [2] (ii) Write an ionic equation to represent the equation. ………………………………………………………………………….……………...……………. [1] [Total: 5]

PRSS_2023_S4E_PRELIM_CHEM_ 6092_P2 8 A6 Copper is a transition element. It can act as a catalyst in the form of an element or a compound. (a) State two other chemical properties of transition elements which make them different from Group I elements. 1 ……………………………………………………………………………………………………………….. 2 …………………………………………………………………………………………………………… [2] (b) Copper can exist in the form of copper(II ) ox ide. When copper (II) oxide is heated at 800° C, it decomposes to form two products as shown in the following chemical equation. 4CuO → 2Cu2O + O2 (i) Explain, in terms of electron transfer, why CuO is described as an oxidising agent. …………………………………………….…………………………………………….………………. ………………………………………………………………………….……………...……………. [1] (ii) Explain, in terms of oxidation states, why CuO is described as a reducing agent. ………………………………………………………………………………………….………………. ………………………………………………………………………………………...……………. [1] (c) Copper metal is obtained when scrap iron is added to aqueous copper(II) sulfate. (i) Describe two observations and explain why this is possible. Include a chemical equation to support your answer. …………………………………