SJI 2022 Y4 Prelim Chemistry 6092 P2 QP

ST JOSEPH’S INSTITUTION PRELIMINARY EXAMINATION 2022 (YEAR 4) CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Candidates answer on the Question Paper. No Additional Materials are required. 6092/02 19 August 2022 1 hour 45 minutes (10:40 – 12:25) READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black fluid ink pen. You may use a soft pencil for any diagrams, graphs or rough working. 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. The number of marks is given in brackets [ ] at the end of each question or part question. The use of an approved scientific calculator is expected, where appropriate. A copy of the Periodic Table is printed on page 2. For Examiner’s Use Section A / 50 Section B / 30 Total / 80 This document consists of 22 printed pages including this cover page.

2

3 Section A (50 marks) Answer all questions in this section in the spaces provided. A1 Study the flowchart below and answer the following questions. (a) Identify substances W, X and Y. W: ………………………………………………………….. X: …………………………………………………………... Y: ……………………………………………………….….. [3] (b) Describe a chemical test to confirm the identity of the colourless gas Z. ..………………..…………………………………………………………………………… ………………….………………………………………………………………………..[1] [Total: 4] add aqueous ammonia dropwise then in excess green solution colourless gas Z + mixture of white and green precipitate formed but white precipitate subsequently dissolved add dilute sulfuric acid white precipitate Y formed metal W and colourless solution X filter mixture and add acidified aqueous barium nitrate to filtrate

4 A2 Silicon t etrachloride, SiCl4, and ethoxyethane, (C 2H5)2O, are both liquids at roo m temperature and pressure. An experiment is performed to react silicon tetrachloride with ethoxyethane to produce two oxochlorides, Si2OCl6 and Si3O2Cl8. (a) (i) The temperature of the experiment is increased. State the effect of increasing temperature on the rate of reaction. Explain your answer in terms of reacting particles. ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ………………..……………………................................................................[2] (ii) A student sugge sted that the rate of reaction of the experiment can be increased by increasing the pressure. Do you agree? Explain your answer. ……………..………………………………………………………………………… ………………..……………………................................................................[1] (b) The oxochlorides that are formed can be reacted with water to convert a ll the chlorine atoms in the oxochlorides into chloride ions. (i) Calculate the number of moles of chloride ions produced when 1.00 g of the oxochloride, Si2OCl6, completely reacts with water. [1]

5 (ii) Calculate the number of moles of chloride ions produced when 1.00 g of the oxochloride, Si3O2Cl8, completely reacts with water. [1] (c) Excess aqueous silver nitrate is added separately to the solutions formed by the two different oxo chlorides, Si2OCl6 and Si3O2Cl8. This helps to remove the chloride ions by forming a precipitate. (i) Write an ionic equation for the formation of the precipitate. [1] (ii) Using y our answers in (b) and (c)(i), identify the oxochloride that will produce 3.03 g of precipitate. Explain how you arrived at your answer. ……………..………………………………………………………………………… ………………..……………………................................................................[2] [Total: 8]

6 A3 (a) The Medupi Power Station is a coal -fired power station in South Africa. When coal is burnt in the power station, one of the pollutants formed is nitrogen dioxide. (i) Describe how nitrogen dioxide is formed in the power station. ……………..………………………………………………………………………… ………………..……………………................................................................[1] (ii) Analysis of soil samples in the region in close proximity to the power station showed a high nitrate ion content. Suggest the reason for the above. ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ………………..……………………................................................................[2] (iii) Over a p eriod of time, marble structures near t he power station were observed to be corroding. Write the chemical equation for the reaction which resulted in the corrosion of the marble structures. [1] (b) The following message was displayed on the side of a bus in Singapore. This bus is more environmentally friendly than a car. 40 cars = 230 000 kg of carbon dioxide per year This bus = 3200 kg of carbon dioxide per year (i) Describe the environmental problem caused by carbon dioxide. ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ………………..……………………................................................................[2]

7 (ii) Using the information provided, explain h ow the environmental pro blem caused by carbon dioxide in (b)(i) can be reduced. ……………..………………………………………………………………………… ……………..………………………………………………………………………… ……………..………………………………………………………………………… ………………..……………………................................................................[2] (c) The Haber Process is used to manufacture ammonia in the chemical industry. (i) State the optimum conditions used in the Haber Process. ………………..……………………................................................................[1] (ii) Explain why the yield of ammonia produced in the Haber Process can never be 100 %. ……………..………………………………………………………………………… ………………..……………………................................................................[1] [Total: 10]

8 A4 Zinc can be obtained from zinc blende (ZnS) in a two-step process. In Step 1, zinc blende is roasted in air and converted into zinc oxide according to the equation shown below. 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) In Step 2, the zinc oxide formed in Step 1 is then converted into zinc by reacting zinc oxide with the same gaseous reducing agent used in the extraction of iron. (a) Explain, in terms of oxidation states, why the re action shown in Step 1 is a redox reaction. ..………………..…………………………………………………………………………… ..………………..…………………………………………………………………………… ………………….………………………………………………………………………..[ 2] (b) Write the chemical equation with state symbols for the reaction in Step 2. [2] (c) Two iron rods are coated, one with zinc and the other with copper. Both rods were damaged with the ir coating scratched when they were piled into the ground to construct a structure. The damaged iron rods were exposed to the wet ground and air. (i) Describe what will be observed on the exposed iron surfaces of both rods after a few days. ……………..………………………………………………………………………… ………………..……………………................................................................[2] (ii) Explain your answer in (c)(i). ………