2024 TMJC H2 Chem Prelim P3 (QP)

CANDIDATE NAME CIVICS GROUP H2 CHEMISTRY 9729/03 Paper 3 Free Response 17 September 2024 2 hours Candidates answer on the Question Paper. Additional materials: Data Booklet This document consists of 33 printed pages and 1 blank page. TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION READ THESE INSTRUCTIONS FIRST Write your name and Civics Group in the spaces at the top of the page. 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. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 15 2 / 21 3 / 24 Section B 4 / 20 OR 5 / 20 Total

2 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry Section A Answer all questions from this section. 1 Ethanoic acid , CH 3COOH, is a common precursor used in industries to synthesise more complex compounds. (a) Ethanoic acid has a Ka value of 1.74 × 10–5. (i) Calculate the pH of 0.200 mol dm–3 ethanoic acid to 1 decimal place. [1] (ii) Write the Ka expression for ethanoic acid. [1]

3 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry [Turn over (b) An aliquot of 25.0 cm3 of 0.200 mol dm –3 of ethanoic acid is titrated with 25.0 cm 3 of 0.200 mol dm–3 NaOH solution. (i) Explain, with the aid of a chemical equation, why the pH at equivalence point is alkaline. [2] (ii) A buffer was formed during this titration. Write a chemical equation to show how the buffer solution resists pH change when a small amount of NaOH is added. [1] (iii) By using the Ka value from (a), calculate the pH of the solution to 2 decimal places when 15.0 cm3 of NaOH was added. [3]

4 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry (c) A sample of industrial waste contains only hydrochloric acid and ethanoic acid. 50.0 cm3 of the industrial waste was collected in a volumetric flask and topped up to 250 cm 3. A 25.0 cm3 sample of the resultant solution was then titrated using 0.200 mol dm–3 NaOH solution, giving two equivalence points at 12.40 cm 3 and 23.55 cm 3. The first equivalence point is for the neutralisation reaction with HCl. (i) Both hydrochloric acid and ethanoic acid are Br ønsted-Lowry acids. Define the term Brønsted-Lowry acid. [1] (ii) Calculate the concentration of hydrochloric acid present in the 50.0 cm3 sample of industrial waste. [3] (iii) Hence, calculate an approximate value for the pH of the industrial waste. Give your answer to 1 decimal place. [1] (iv) Sketch the shape of the titration curve and circle the portion that represents a buffer solution. No numerical pH values are needed. [2]

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6 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry 2 Cobalt is a critical component in lithium-ion batteries, which are essential for powering electric vehicles and portable electronics due to their high energy density and reliability. (a) The following sequence of reactions in Fig. 2.1 involves cobalt and its complexes. Fig. 2.1 (i) State the type of reaction that occurred in step 3 and the role of H2O2 in step 8. [2] (ii) Given that complex A is square planar in shape, suggest the identities of complexes A and B. [2] (iii) When solutions of [Co(H 2O)6]2+ and [Fe(H 2O)6]3+ are each mixed with sodium carbonate solution, different reactions occur. [Fe(H2O)6]3+ produces effervescence of CO2 but not [Co(H2O)6]2+. Explain why [Fe(H 2O)6]3+ results in the evolution of carbon dioxide gas when reacted with carbonate ions. [2]

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8 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry (b) Co3O4, also known as cobalt tetroxide, is a black ionic compound that contains both Co2+ and Co3+ ions. (i) Suggest the ratio of the two different cobalt ions in Co3O4. [1] Cobalt tetroxide can be reduced to cobalt oxide at 900 oC. Co3O4(s) 3 CoO(s) + ½ O2(g) HꝊrxn 1 Some relevant thermochemical data is listed in the Table 2.1 below. Table 2.1 enthalpy change value / kJ mol–1 HꝊat Co(s) +426 HꝊf O2–(g) +850 Lattice energy of CoO(s) –3910 HꝊf Co3O4(s) –910 (ii) Using the data given in Table 2.1 and relevant information from the Data Booklet, show that the standard enthalpy change of formation of CoO, HꝊf CoO, is –237 kJ mol–1. [3] (iii) Hence, determine the enthalpy change of reaction, HꝊrxn 1. [1]

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10 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry (c) Cobalt oxide exhibits behaviour like aluminium oxide in its chemical properties and reactions, displaying both acidic and basic characteristics depending on the reaction environment. (i) In your laboratory, you have three unidentified substances: magnesium oxide, silicon oxide and aluminium oxide. Describe a method to identify each substance based on their reactions with acids and bases. Provide relevant chemical equations for these reactions, describing the differences in their observable behaviours. [4] (ii) Draw a melting point trend graph for period 3 oxides. Explain why MgO has a higher melting point than Na2O. [3]