Pasir Ris 2024 4E Chem Prelim P2

Name Class Register No. SECONDARY 4 EXPRESS PRELIMINARY EXAMINATION 2024 CHEMISTRY Paper 2 Tuesday 1040 – 1225 6092/02 20 Aug 2024 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 one question 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 24. The use of an approved scientific calculator is expected, where appropriate. This document consists of 24 printed pages, including the cover page. Setter: Mr Chua Khoon Wee [Turn over Pasir Ris Secondary School For Examiner’s Use Section A Section B Total

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 2 Section A Answer all the questions in the spaces provided. The total mark for this section is 70. 1 Select oxides from the list in Table 1.1 to answer the following questions. You may use each oxide once, more than once or not at all. Table 1.1 calcium oxide carbon monoxide copper(II) oxide nitrogen monoxide nitrogen dioxide silicon dioxide sulfur dioxide zinc oxide (a) Which is an acidic oxide with a giant molecular structure? …………………………………………………………………………………………………………... [1] (b) Which oxide reacts only with acids but not bases? …………………………………………………………………………………………………………... [1] (c) Which oxide reacts with both acids and alkalis? …………………………………………………………………………………………………………... [1] [Total: 3]

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 3 2 An unknown solution A contains a mixture of two salts. A series of chemical tests was carried out and the observations were recorded as shown in Fig. 2.1. Fig. 2.1 (a) Suggest the identity of substances B, C, D and E. (i) B ………………………………… (ii) C ………………………………… (ii) D ………………………………… (iv) E ………………………………… [4] (b) Suggest two possible salts that are present in the unknown solution A. ………………………………………………... and …………………………………………………… [2] [Total: 6]

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 4 3 Table 3.1 shows the formulae and melting points of hydrides formed from two elements in Period 3. Table 3.1 formula of element Group number formula of hydride melting point of hydride / °C Mg 2 MgH2 327 Al 13 AlH3 150 (a) Fig. 3.2 shows the arrangement of electrons in aluminium hydride. Fig. 3.2 (i) Identify the type of bonding present in aluminium hydride. Explain your answer. ......................................................................................................................................... ......................................................................................................................................... [2] (ii) Explain why the arrangement of electrons in aluminium hydride is unusual. ......................................................................................................................................... ......................................................................................................................................... [1]

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 5 (b) Magnesium has a different type of bonding present compared to aluminium hydride. (i) Draw a ‘dot -and-cross’ diagram to show the bonding in magnesium hydride. Show outer electrons only. [2] (ii) Explain, in terms of structure and bonding, why the melting point of magnesium hydride is much higher than that of aluminium hydride. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... [3] [Total: 8]

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 6 4 Chalcopyrite, CuFeS 2, is a copper ore containing both the copper( II) and iron( II) ions. Copper is extracted from chalcopyrite by first heating it with silicon dioxide in air to form copper(I) sulfide. 2CuFeS2 + 2SiO2 + 4O2 → Cu2S + 2FeSiO3 + 3SO2 The copper(I) sulfide is converted to copper by blasting it with hot air. Cu2S + O2 → 2Cu + SO2 The copper formed is called blister copper. It is brittle and 96.0% pure. (a) The extraction of copper from chalcopyrite can pose large environmental problem if it is not properly controlled. Identify which substance may be a pollutant and describe the problems it can cause. …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... …………………………………………………………………………………………………………... [2] (b) Fig. 4.1 shows the cross-section of a tank used for the purification of copper metal. Fig. 4.1 (i) Suggest a suitable electrolyte for the purification process. ......................................................................................................................................... [1] + –

PRSS_2024_S4E_PRELIM_CHEM_ 6092_P2 7 (ii) Write the ionic half equations, with state symbols, for the reaction that takes place at the copper plate and blister copper respectively during the purification. copper plate: ................................................................................................................... blister copper: .................................................................................................................. [2] (iii) Explain why the electrolyte for this reaction may be used continuously without changing or replacing. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... [2] (c) 2.00 tonnes of blister copper is obtained during an extraction of copper from chalcopyrite. Calculate the mass of chalcopyrite used in the reaction. [1 tonne = 1000 kg] [2] (d) Zinc can be added to blister copper in a 1:9 ratio to make bronze, an alloy of copper. Bronze is a very hard and strong material. It also has relatively good electrical conductivity. (i) Explain why bronze is harder and stronger than blister copper. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ...............................................................................................................................