St Gabriel 2024 Prelim Sec 4E Chemistry P2 & MS

St. Gabriel’s Secondary School 2024 ‘O’ Preliminary Examination Subject : Chemistry Paper : 6092 / 02 Level/Stream : Secondary 4 (Express) Duration : 1 hour 45 minutes Date : 21 August 2024 No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, index number and class 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 on page 24. The use of an approved scientific calculator is expected, where appropriate. 2023_EYE_Sec 3N Science (Chemistry) FOR EXAMINER’S USE Section A 70 Section B 10 TOTAL 80 This question paper consists of 24 printed pages. Name: …………………………………………………… ( ) Class: Sec ………………..

2 SGSS/Chemistry/P2/4E/Prelim/2024 Section A Answer all questions. 1 Fig. 1.1 shows part of the Periodic Table. The elements are represented by the letters M, Q, R, T, W, X, Y and Z. Y R W X Z M T Q Fig. 1.1 Select elements from the Periodic Table to answer the following questions. You may use each element once, more than once or not at all. (a) Which two elements react together most vigorously? ………………………………………………………………………………………………….. [1] (b) Which element forms an ion with a charge of –2? ………………………………………………………………………………………………….. [1] (c) Which element has a high density? ………………………………………………………………………………………………….. [1] (d) What is the formula of the compound formed when W reacts with Y? ………………………………………………………………………………………………….. [1] (e) Which element constitutes about 1% of dry air? ………………………………………………………………………………………………….. [1] [Total: 5]

3 SGSS/Chemistry/P2/4E/Prelim/2024 2 Sodium carbonate ionises in water according to the following equation. Na2CO3(s) + H2O(l) ⇌ 2Na+(aq) + HCO3–(aq) + OH–(aq) Fig. 2.1 shows the effect of pressure and temperature on the concentration of hydroxide ions produced per mole of sodium carbonate. concentration of OH– ions pressure Fig. 2.1 (a) (i) Sodium carbonate is a weak alkali. Explain what a weak alkali is. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [1] (ii) State the colour of the resulting mixture when a few drops of Universal Indicator are added to a solution of sodium carbonate. …………………………………………………………………………………………… [1] (b) (i) Describe how temperature and pressure affect the concentration of hydroxide ions produced during the ionisation of sodium carbonate in water. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [2] (ii) Explain the effect of pressure on concentration of hydroxide ions as stated in (b)(i). ………………………………………………………………………………………………….. …………………………………………………………………………………………… [1] 70 C 20 C

4 SGSS/Chemistry/P2/4E/Prelim/2024 (c) Sulfuric acid is a dibasic acid which reacts with the hydroxide ions and hydrogencarbonate ions produced during the ionisation of sodium carbonate. (i) Write an ionic equation, with state symbols, for the reaction between sulfuric acid and the ions produced. …………………………………………………………………………………………… [2] (ii) Suggest why the formation of the products in (c)(i) drives the dissociation of sodium carbonate in water and allows it to react completely with sulfuric acid. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [1] [Total: 8]

5 SGSS/Chemistry/P2/4E/Prelim/2024 3 Fig. 3.1 shows some reactions involving substances A, B, C and D. white precipitate B white solid D strong heating + BaCl2 (aq) white solid + H2O solution A aqueous calcium hydroxide gas produced forms white precipitate in limewater gas C produced, turns damp red litmus paper blue Fig. 3.1 (a) Identify substances A, B and D. A : ………………………………………… B : ………………………………………… D : ………………………………………… [3] (b) Substance C was passed through aqueous copper( II) sulfate until no further change was observed. Describe and explain the observation(s) seen during the reaction. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………….. [3] [Total: 6]

6 SGSS/Chemistry/P2/4E/Prelim/2024 4 Zinc is mainly obtained from sulfide ores such as zinc blende, ZnS. These sulfides ores typically contain other metal impurities such as cadmium, iron and silver. Extraction of zinc from zinc blende takes place in a few stages. Stage 1: Zinc blende is roasted in air to convert zinc sulfide to zinc oxide and sulfur dioxide. 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) Stage 2: The roasted oxide is added to a hot solution of sulfuric acid to produce zinc sulfate. Any iron impurities present in the mixture is converted to iron(III) sulfate. Stage 3: Ammonium sulfate is added to the mixture to remove iron(III) sulfate as a jarosite precipitate, NH4Fe3(SO4)2(OH)6. Stage 4: Powdered zinc is added to the mixture to precipita te metal impurities such as cadmium and silver from zinc sulfate solution. Stage 5: Zinc is extracted through electrolysis of zinc sulfate solution using inert electrodes. (a) The word equation for the removal of iron(III) sulfate in Stage 2 is as shown. iron(III) sulfate + ammonium sulfate + water → jarosite + sulfuric acid Complete the equation for the reaction that takes place. 3Fe2(SO4)3 [2] (b) (i) Explain how the powdered zinc added in Stage 4 helps to remove the remaining metal impurities. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [2] (ii) State one additional process that needs to be carried out in Stage 4 before the products can be used in Stage 5. …………………………………………………………………………………………… [1]

7 SGSS/Chemistry/P2/4E/Prelim/2024 (c) (i) Write ionic equations, with state symbols, for the reactions occurring at each electrode in Stage 5. anode: ………………………………………………………………………………….. cathode: ………………………………………………………………………………… [2] (ii) State how the product(s) formed at one of the electrodes in (c)(i) is unusual. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [1] (iii) Describe and explain one change in the electrolyte during the electrolysis of zinc sulfate solution in Stage 5. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………… [2] (iv) Describe a simple test that can be conducted to support your explanation in (c)(ii). ………………………………………………………………………………………………….. …………………………………………………………………………………………… [1] [Total: 11]

8 SGSS/Chemistry/P2/4E/Prelim/2024 5 Carboxylic acids readily undergo reaction with phosphorus( V) chloride at room temperature and pressure to form organic compounds known as acid chlorides accordin