Woodlands Prelim P2

6092/02/Prelim/24 EXPRESS EXPRESS EXPRESS Name: ........................................................................ ( ) Class: ................ WOODLANDS SECONDARY SCHOOL PRELIMINARY EXAMINATION 2024 Level: Secondary 4 Express Marks: 80 Subject: Pure Chemistry Day: Tuesday Paper: 6092/02 Date: 20 August 2024 Duration: 1 hour 45 minutes Time: 0750 – 0935 hours READ THESE INSTRUCTIONS FIRST Write your name, index number and class on all the work that 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 on page 24. The use of an approved scientific calculator is expected, where appropriate. DO NOT TURN THE PAGE UNTIL YOU ARE TOLD TO DO SO. This document consists of 22 printed pages and 2 blank pages. FOR EXAMINER’S USE Section A Section B Total /70 /10 /80

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3 6092/02/Prelim/24 EXPRESS EXPRESS EXPRESS Section A Answer all questions. 1 Use the list of substances to answer the following questions. magnesium oxide silicon dioxide sulfur dioxide carbon monoxide zinc oxide carbon dioxide (a) Name all substances which are ionic compounds. ........................................................................................................................[1] (b) Which substance has a similar structure like diamond? ........................................................................................................................[1] (c) Which substance is an amphoteric oxide? ........................................................................................................................[1] (d) Which two substances can dissolve in water to form solutions with pH less than 7? ........................................................................................................................[1] (e) Which gaseous substance is neutral? ........................................................................................................................[1] [Total: 5]

4 6092/02/Prelim/24 EXPRESS EXPRESS EXPRESS 2 When ammonia gas reacts with hydrogen chloride gas, white fumes of ammonium chloride are formed. NH3 + HCl ⇌ NH4Cl Fig. 2.1 shows watch-glasses of aqueous ammonia and concentrated hydrochloric acid being placed near each other on a table. At first, no white fumes were seen. After a short time, white fumes were seen between the watch-glasses and were seen nearer to the watch-glass of hydrochloric acid. Fig. 2.1 (a) Explain these observations using the kinetic particle theory. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ........................................................................................................................[2] (b) Draw a dot-and-cross diagram to show the bonding in ammonia. Show only the outermost electrons. [2] [Total: 4]

5 6092/02/Prelim/24 EXPRESS EXPRESS EXPRESS 3 Hydrogen fluoride, HF, has a simple molecular structure. It is soluble in water. (a) Suggest one other physical property of hydrogen fluoride. ............................................................................................................................ ........................................................................................................................[1] (b) Hydrogen fluoride dissolves in water to form dilute hydrofluoric acid, a weak acid. With the help of an equation, explain why hydrofluoric acid is a weak acid. ............................................................................................................................ ............................................................................................................................ ........................................................................................................................[2] (c) Dilute hydrofluoric acid reacts with excess magnesium to form magnesium fluoride and hydrogen gas. (i) Write a balanced chemical equation for the reaction. ............................................................................................................[1] (ii) Calculate the volume of gas produced if the acid solution contains 0.200 g of hydrofluoric acid. volume = ................................ [2] (d) Explain, in terms of structure and bonding, why magnesium fluoride has a high melting point. ............................................................................................................................ ............................................................................................................................ ........................................................................................................................[2] [Total: 8]

6 6092/02/Prelim/24 EXPRESS EXPRESS EXPRESS 4 A solid E was added to nitric acid. The tests and observations are outlined in Fig. 4.1. Fig. 4.1 (a) Identify the following substances. (i) gas G ............................................................................................................[1] (ii) gas J ............................................................................................................[1] (iii) solid E ............................................................................................................[1] (b) Darren wanted to prepare a pure dry sample of zinc nitrate. He decided to use zinc oxide and nitric acid. Using the reactants mentioned, describe the steps Darren must carry out in order to obtain a pure, dry sample of zinc nitrate. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ........................................................................................................................[3] [Total: 6]

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