GESS 4Exp Pure Chem Prelim 2024 P2

This document consists of 23 printed pages. GAN ENG SENG SCHOOL Preliminary Examination 2024 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Candidates answer on the Question Paper. No Additional Materials are required. 6092/02 21 August 2024 1 hour 45 minutes READ THESE INSTRUCTIONS FIRST Write your name, class and index number 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 23. The use of an approved scientific calculator is expected, where appropriate. For Examiner‘s Use Section A 70 Section B 10 Q9 Q10 Total 80 *Circle where appropriate

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 2 Section A Answer all questions. 1 The equations below show reactions involving elements A to E. Element A: 2 A + 2 H2O → 2 AOH + H2 Element B: BO2 + 2 NaOH → Na2BO3 + H2O Element C: C2 + 2 Br– → 2 C– + Br2 Element D: D + Cu2+ → D2+ + Cu Element E: E2O3 + 6 H+ → 2 E3+ + 3 H2O Each letter represents an element found in Period 3 of the Periodic Table (sodium to argon). The letters do not represent the actual symbols of the elements. (a) Identify elements A to E. A …………………… B …………………… C …………………… D …………………… E …………………… [5] (b) Classify each element as having undergone oxidation, reduction or neither. Put a tick (ü) in each row. element undergone oxidation undergone reduction neither oxidised nor reduced A B C D E [3] [Total: 8]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 3 2 Gas chromatography can be used to separate a mixture of gases as shown below. The retention time is the time it takes each component to travel through the column. (a) The gases entering the column must be dry to avoid interference from water molecules. Suggest how the gases may be dried. …………………………………………………………………………………………….. [1] (b) Vegetable oils can be changed into bio-diesel for use in diesel engines. Gas chromatography is used to identify the methyl esters in a sample of bio-diesel. The table shows the retention time for three methyl esters. methyl ester Mr retention time / min lauric 214 1.6 palmitic 270 3.1 stearic 298 3.9 One factor affecting retention time is the rate of diffusion. (i) The data in the table suggests a correlation between the relative molecular mass and the retention time. Describe this correlation. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 4 (ii) The experiment is repeated with the column at a higher temperature. Suggest and explain how this will affect the retention times. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [3] (c) Unlike gas chromatography, paper chromatography compares Rf values instead of retention times. Besides temperature, state one factor that affects Rf values. …………………………………………………………………………………………….. [1] [Total: 6]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 5 3 The diagrams show four different types of acid solutions. The acid molecule is represented as HA. The ions formed in solution are represented as H+ and A–. 1 2 3 4 (a) State which diagram represents a dilute solution of a weak acid. Explain your answer. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [3] (b) Explain why sulfuric acid is not represented by the diagrams above. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [2] (c) Equal volumes of ethanoic acid and hydrochloric acid of the same concentration was allowed to react completely with magnesium. State, with a reason, whether the volume of hydrogen gas produced will differ. …………………………………………………………………………………………….. [1] (d) An unknown bottle is suspected to contain dilute sulfuric acid. Outline a chemical test that can be used to confirm this. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [2] [Total: 8]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 6 4 Two chlorine-containing organic molecules shown below are known to cause harm to the environment. dichlorodifluoromethane (CFC-12) polyvinyl chloride (PVC) (a) In the presence of sunlight, CFC-12 decomposes into chlorine atoms, which deplete the ozone layer by causing the breakdown of ozone in a two-step reaction. Cl + O3 → ClO + O2 ClO + O3 → 2 O2 + Cl (i) Explain why the depletion of the ozone layer would be undesirable to humans. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] (ii) Use the equations to write an overall equation for the reaction. ……………………………………………………………………………………. [2] (iii) Explain how the equations show that chlorine atoms act as a catalyst for the breakdown of ozone. ……………………………………………………………………………………. [1]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 7 (iv) Chlorine exists as two stable isotopes, with chlorine-35 (35Cl) reacting faster with ozone than chlorine-37 (37Cl). Studying the 37Cl to 35Cl ratio helps scientists model the rate of ozone depletion more accurately. Complete Table 4.1 to show the number of subatomic particles in each isotope of chlorine. Table 4.1 isotope 35Cl 37Cl number of electrons number of neutrons number of protons [2] (b) (i) Draw the structure of the monomer used to make polyvinyl chloride (PVC). [1] (ii) Describe one pollution problem caused by non-biodegradable plastics such as polyvinyl chloride (PVC). ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iii) The best way of disposing of plastic waste is recycling to form new plastics. State an advantage of recycling plastics made from petroleum. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] [Total: 10]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 8 5 The reaction between metals and water can be studied using the apparatus shown. A fixed mass of calcium was allowed to react completely with water. The volume of gas given off was recorded at fixed time intervals during the reaction. The experiment was repeated using strontium but keeping all the conditions the same. The graph obtained from the results is shown below. (a) Explain how the graph shows that strontium is more reactive than calcium. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [1]

GESS 4EXP Chemistry 6092/02 PRELIM 2024_JAN 9 (i) Calculate the average rate of reaction, in cm3/s, for the reaction between strontium and water. average rate of reaction = …………. cm3/s [1] (ii) Explain how the graph shows that the reaction between calcium and water was not complete at 100 seconds after the reaction started. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (b) The solution formed at the end of the reaction between strontium and water was tested with Universal Indicator. The indicator turned purple. Explain this observation with the aid of a chemical equation. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [3] (c) The electrolysis of a molten electrolyte is one